Re: [PATCH RFC net-next 08/14] bpf: add eBPF verifier
From: Chema Gonzalez <hidden>
Date: 2014-07-02 22:22:17
Also in:
lkml, netdev
I'm in the process of reading the code, and got some questions/comments. -Chema On Fri, Jun 27, 2014 at 5:06 PM, Alexei Starovoitov [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Safety of eBPF programs is statically determined by the verifier, which detects: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention It checks that - R1-R5 registers statisfy function prototype - program terminates - BPF_LD_ABS|IND instructions are only used in socket filters It is configured with: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); reports argument types of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match prototype More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <redacted> --- Documentation/networking/filter.txt | 233 ++++++ include/linux/bpf.h | 48 ++ include/uapi/linux/bpf.h | 1 + kernel/bpf/Makefile | 2 +- kernel/bpf/syscall.c | 2 +- kernel/bpf/verifier.c | 1431 +++++++++++++++++++++++++++++++++++ 6 files changed, 1715 insertions(+), 2 deletions(-) create mode 100644 kernel/bpf/verifier.cdiff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index e14e486f69cd..05fee8fcedf1 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt@@ -995,6 +995,108 @@ BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and 2 byte atomic increments are not supported. +eBPF verifier +------------- +The safety of the eBPF program is determined in two steps. + +First step does DAG check to disallow loops and other CFG validation. +In particular it will detect programs that have unreachable instructions. +(though classic BPF checker allows them) + +Second step starts from the first insn and descends all possible paths. +It simulates execution of every insn and observes the state change of +registers and stack. + +At the start of the program the register R1 contains a pointer to context +and has type PTR_TO_CTX. +If verifier sees an insn that does R2=R1, then R2 has now type +PTR_TO_CTX as well and can be used on the right hand side of expression. +If R1=PTR_TO_CTX and insn is R2=R1+R1, then R2=INVALID_PTR, +since addition of two valid pointers makes invalid pointer. + +If register was never written to, it's not readable: + bpf_mov R0 = R2 + bpf_exit +will be rejected, since R2 is unreadable at the start of the program. + +After kernel function call, R1-R5 are reset to unreadable and +R0 has a return type of the function. + +Since R6-R9 are callee saved, their state is preserved across the call. + bpf_mov R6 = 1 + bpf_call foo + bpf_mov R0 = R6 + bpf_exit +is a correct program. If there was R1 instead of R6, it would have +been rejected. + +Classic BPF register X is mapped to eBPF register R7 inside sk_convert_filter(), +so that its state is preserved across calls. + +load/store instructions are allowed only with registers of valid types, which +are PTR_TO_CTX, PTR_TO_MAP, PTR_TO_STACK. They are bounds and alignment checked. +For example: + bpf_mov R1 = 1 + bpf_mov R2 = 2 + bpf_xadd *(u32 *)(R1 + 3) += R2 + bpf_exit +will be rejected, since R1 doesn't have a valid pointer type at the time of +execution of instruction bpf_xadd. + +At the start R1 contains pointer to ctx and R1 type is PTR_TO_CTX. +ctx is generic. verifier is configured to known what context is for particular +class of bpf programs. For example, context == skb (for socket filters) and +ctx == seccomp_data for seccomp filters. +A callback is used to customize verifier to restrict eBPF program access to only +certain fields within ctx structure with specified size and alignment. + +For example, the following insn: + bpf_ld R0 = *(u32 *)(R6 + 8) +intends to load a word from address R6 + 8 and store it into R0 +If R6=PTR_TO_CTX, via is_valid_access() callback the verifier will know +that offset 8 of size 4 bytes can be accessed for reading, otherwise +the verifier will reject the program. +If R6=PTR_TO_STACK, then access should be aligned and be within +stack bounds, which are [-MAX_BPF_STACK, 0). In this example offset is 8, +so it will fail verification, since it's out of bounds. + +The verifier will allow eBPF program to read data from stack only after +it wrote into it. +Classic BPF verifier does similar check with M[0-15] memory slots. +For example: + bpf_ld R0 = *(u32 *)(R10 - 4) + bpf_exit +is invalid program. +Though R10 is correct read-only register and has type PTR_TO_STACK +and R10 - 4 is within stack bounds, there were no stores into that location. + +Pointer register spill/fill is tracked as well, since four (R6-R9) +callee saved registers may not be enough for some programs. + +Allowed function calls are customized with bpf_verifier_ops->get_func_proto() +For example, skb_get_nlattr() function has the following definition: + struct bpf_func_proto proto = {RET_INTEGER, PTR_TO_CTX}; +and eBPF verifier will check that this function is always called with first +argument being 'ctx'. In other words R1 must have type PTR_TO_CTX +at the time of bpf_call insn. +After the call register R0 will be set to readable state, so that +program can access it. + +Function calls is a main mechanism to extend functionality of eBPF programs. +Socket filters may let programs to call one set of functions, whereas tracing +filters may allow completely different set. + +If a function made accessible to eBPF program, it needs to be thought through +from security point of view. The verifier will guarantee that the function is +called with valid arguments. + +seccomp vs socket filters have different security restrictions for classic BPF. +Seccomp solves this by two stage verifier: classic BPF verifier is followed +by seccomp verifier. In case of eBPF one configurable verifier is shared for +all use cases. + +See details of eBPF verifier in kernel/bpf/verifier.c + eBPF maps --------- 'maps' is a generic storage of different types for sharing data between kernel@@ -1064,6 +1166,137 @@ size. It will not let programs pass junk values as 'key' and 'value' to bpf_map_*_elem() functions, so these functions (implemented in C inside kernel) can safely access the pointers in all cases. +Understanding eBPF verifier messages +------------------------------------ + +The following are few examples of invalid eBPF programs and verifier error +messages as seen in the log: + +Program with unreachable instructions: +static struct sock_filter_int prog[] = { + BPF_EXIT_INSN(), + BPF_EXIT_INSN(), +}; +Error: + unreachable insn 1 + +Program that reads uninitialized register: + BPF_ALU64_REG(BPF_MOV, BPF_REG_0, BPF_REG_2), + BPF_EXIT_INSN(), +Error: + 0: (bf) r0 = r2 + R2 !read_ok + +Program that doesn't initialize R0 before exiting: + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_1), + BPF_EXIT_INSN(), +Error: + 0: (bf) r2 = r1 + 1: (95) exit + R0 !read_ok + +Program that accesses stack out of bounds: + BPF_ST_MEM(BPF_DW, BPF_REG_10, 8, 0), + BPF_EXIT_INSN(), +Error: + 0: (7a) *(u64 *)(r10 +8) = 0 + invalid stack off=8 size=8 + +Program that doesn't initialize stack before passing its address into function: + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), + BPF_EXIT_INSN(), +Error: + 0: (bf) r2 = r10 + 1: (07) r2 += -8 + 2: (b7) r1 = 1 + 3: (85) call 1 + invalid indirect read from stack off -8+0 size 8 + +Program that uses invalid map_id=2 while calling to map_lookup_elem() function: + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 2), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), + BPF_EXIT_INSN(), +Error: + 0: (7a) *(u64 *)(r10 -8) = 0 + 1: (bf) r2 = r10 + 2: (07) r2 += -8 + 3: (b7) r1 = 2 + 4: (85) call 1 + invalid access to map_id=2 + +Program that doesn't check return value of map_lookup_elem() before accessing +map element: + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0), + BPF_EXIT_INSN(), +Error: + 0: (7a) *(u64 *)(r10 -8) = 0 + 1: (bf) r2 = r10 + 2: (07) r2 += -8 + 3: (b7) r1 = 1 + 4: (85) call 1 + 5: (7a) *(u64 *)(r0 +0) = 0 + R0 invalid mem access 'map_value_or_null' + +Program that correctly checks map_lookup_elem() returned value for NULL, but +accesses the memory with incorrect alignment: + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), + BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), + BPF_EXIT_INSN(), +Error: + 0: (7a) *(u64 *)(r10 -8) = 0 + 1: (bf) r2 = r10 + 2: (07) r2 += -8 + 3: (b7) r1 = 1 + 4: (85) call 1 + 5: (15) if r0 == 0x0 goto pc+1 + R0=map_value1 R10=fp + 6: (7a) *(u64 *)(r0 +4) = 0 + misaligned access off 4 size 8 + +Program that correctly checks map_lookup_elem() returned value for NULL and +accesses memory with correct alignment in one side of 'if' branch, but fails +to do so in the other side of 'if' branch: + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0), + BPF_EXIT_INSN(), + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 1), + BPF_EXIT_INSN(), +Error: + 0: (7a) *(u64 *)(r10 -8) = 0 + 1: (bf) r2 = r10 + 2: (07) r2 += -8 + 3: (b7) r1 = 1 + 4: (85) call 1 + 5: (15) if r0 == 0x0 goto pc+2 + R0=map_value1 R10=fp + 6: (7a) *(u64 *)(r0 +0) = 0 + 7: (95) exit + + from 5 to 8: R0=imm0 R10=fp + 8: (7a) *(u64 *)(r0 +0) = 1 + R0 invalid mem access 'imm' + Testing -------diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 7bfcad87018e..67fd49eac904 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h@@ -47,17 +47,63 @@ struct bpf_map_type_list { void bpf_register_map_type(struct bpf_map_type_list *tl); struct bpf_map *bpf_map_get(u32 map_id); +/* types of values: + * - stored in an eBPF register + * - passed into helper functions as an argument + * - returned from helper functions + */ +enum bpf_reg_type { + INVALID_PTR, /* reg doesn't contain a valid pointer */ + PTR_TO_CTX, /* reg points to bpf_context */ + PTR_TO_MAP, /* reg points to map element value */ + PTR_TO_MAP_CONDITIONAL, /* points to map element value or NULL */ + PTR_TO_STACK, /* reg == frame_pointer */ + PTR_TO_STACK_IMM, /* reg == frame_pointer + imm */ + PTR_TO_STACK_IMM_MAP_KEY, /* pointer to stack used as map key */ + PTR_TO_STACK_IMM_MAP_VALUE, /* pointer to stack used as map elem */ + RET_INTEGER, /* function returns integer */ + RET_VOID, /* function returns void */ + CONST_ARG, /* function expects integer constant argument */ + CONST_ARG_MAP_ID, /* int const argument that is used as map_id */ + /* int const argument indicating number of bytes accessed from stack + * previous function argument must be ptr_to_stack_imm + */ + CONST_ARG_STACK_IMM_SIZE, +}; + /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs * to in-kernel helper functions and for adjusting imm32 field in BPF_CALL * instructions after verifying */ struct bpf_func_proto { s32 func_off; + enum bpf_reg_type ret_type; + enum bpf_reg_type arg1_type; + enum bpf_reg_type arg2_type; + enum bpf_reg_type arg3_type; + enum bpf_reg_type arg4_type; + enum bpf_reg_type arg5_type; +}; + +/* bpf_context is intentionally undefined structure. Pointer to bpf_context is + * the first argument to eBPF programs. + * For socket filters: 'struct bpf_context *' == 'struct sk_buff *' + */ +struct bpf_context; + +enum bpf_access_type { + BPF_READ = 1, + BPF_WRITE = 2 }; struct bpf_verifier_ops { /* return eBPF function prototype for verification */ const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); + + /* return true if 'size' wide access at offset 'off' within bpf_context + * with 'type' (read or write) is allowed + */ + bool (*is_valid_access)(int off, int size, enum bpf_access_type type); }; struct bpf_prog_type_list {@@ -78,5 +124,7 @@ struct bpf_prog_info { void free_bpf_prog_info(struct bpf_prog_info *info); struct sk_filter *bpf_prog_get(u32 prog_id); +/* verify correctness of eBPF program */ +int bpf_check(struct sk_filter *fp); #endif /* _LINUX_BPF_H */diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index ed067e245099..597a35cc101d 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h@@ -381,6 +381,7 @@ enum bpf_prog_attributes { enum bpf_prog_type { BPF_PROG_TYPE_UNSPEC, + BPF_PROG_TYPE_SOCKET_FILTER, }; /* integer value in 'imm' field of BPF_CALL instruction selects which helperdiff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile index 558e12712ebc..95a9035e0f29 100644 --- a/kernel/bpf/Makefile +++ b/kernel/bpf/Makefile@@ -1 +1 @@ -obj-y := core.o syscall.o hashtab.o +obj-y := core.o syscall.o hashtab.o verifier.odiff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 836809b1bc4e..48d8f43da151 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c@@ -554,7 +554,7 @@ static int bpf_prog_load(int prog_id, enum bpf_prog_type type, mutex_lock(&bpf_map_lock); /* run eBPF verifier */ - /* err = bpf_check(prog); */ + err = bpf_check(prog); if (err == 0 && prog->info->used_maps) { /* program passed verifier and it's using some maps,diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c new file mode 100644 index 000000000000..470fce48b3b0 --- /dev/null +++ b/kernel/bpf/verifier.c@@ -0,0 +1,1431 @@ +/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of version 2 of the GNU General Public + * License as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + */ +#include <linux/kernel.h> +#include <linux/types.h> +#include <linux/slab.h> +#include <linux/bpf.h> +#include <linux/filter.h> +#include <linux/capability.h> + +/* bpf_check() is a static code analyzer that walks the BPF program + * instruction by instruction and updates register/stack state. + * All paths of conditional branches are analyzed until 'ret' insn. + * + * At the first pass depth-first-search verifies that the BPF program is a DAG. + * It rejects the following programs: + * - larger than BPF_MAXINSNS insns + * - if loop is present (detected via back-edge) + * - unreachable insns exist (shouldn't be a forest. program = one function)
This seems to me an unnecessary style restriction on user code.
+ * - ret insn is not a last insn
+ * - out of bounds or malformed jumps
+ * The second pass is all possible path descent from the 1st insn.
+ * Conditional branch target insns keep a link list of verifier states.
+ * If the state already visited, this path can be pruned.
+ * If it wasn't a DAG, such state prunning would be incorrect, since it would
+ * skip cycles. Since it's analyzing all pathes through the program,
+ * the length of the analysis is limited to 32k insn, which may be hit even
+ * if insn_cnt < 4K, but there are too many branches that change stack/regs.
+ * Number of 'branches to be analyzed' is limited to 1k
+ *
+ * All registers are 64-bit (even on 32-bit arch)
+ * R0 - return register
+ * R1-R5 argument passing registers
+ * R6-R9 callee saved registers
+ * R10 - frame pointer read-only
+ *
+ * At the start of BPF program the register R1 contains a pointer to bpf_context
+ * and has type PTR_TO_CTX.
+ *
+ * R10 has type PTR_TO_STACK. The sequence 'mov Rd, R10; add Rd, imm' changes
+ * Rd state to PTR_TO_STACK_IMM and immediate constant is saved for further
+ * stack bounds checking
+ *
+ * registers used to pass pointers to function calls are verified against
+ * function prototypes
+ *
+ * Example: before the call to bpf_map_lookup_elem(),
+ * R1 must contain integer constant and R2 PTR_TO_STACK_IMM_MAP_KEY
+ * Integer constant in R1 is a map_id. The verifier checks that map_id is valid
+ * and corresponding map->key_size fetched to check that
+ * [R3, R3 + map_info->key_size) are within stack limits and all that stack
+ * memory was initiliazed earlier by BPF program.
+ * After bpf_table_lookup() call insn, R0 is set to PTR_TO_MAP_CONDITIONAL
+ * R1-R5 are cleared and no longer readable (but still writeable).
+ *
+ * bpf_table_lookup() function returns ether pointer to map value or NULL
+ * which is type PTR_TO_MAP_CONDITIONAL. Once it passes through !=0 insn
+ * the register holding that pointer in the true branch changes state to
+ * PTR_TO_MAP and the same register changes state to INVALID_PTR in the false
+ * branch. See check_cond_jmp_op()
+ *
+ * load/store alignment is checked
+ * Ex: BPF_STX|BPF_W [Rd + 3] = Rs is rejected, because it's misaligned
+ *
+ * load/store to stack bounds checked and register spill is tracked
+ * Ex: BPF_STX|BPF_B [R10 + 0] = Rs is rejected, because it's out of bounds
+ *
+ * load/store to map bounds checked and map_id provides map size
+ * Ex: BPF_STX|BPF_H [Rd + 8] = Rs is ok, if Rd is PTR_TO_MAP and
+ * 8 + sizeof(u16) <= map_info->value_size
+ *
+ * load/store to bpf_context checked against known fields
+ */
+#define _(OP) ({ int ret = OP; if (ret < 0) return ret; })+1 to removing the _ macro. If you want to avoid the 3 lines (is there anything in the style guide against "if ((err=OP) < 0) ..." ?), at least use some meaningful macro name (DO_AND_CHECK, or something like that).
+
+struct reg_state {
+ enum bpf_reg_type ptr;
+ int imm;
+ bool read_ok;
+};
+
+enum bpf_stack_slot_type {
+ STACK_INVALID, /* nothing was stored in this stack slot */
+ STACK_SPILL, /* 1st byte of register spilled into stack */
+ STACK_SPILL_PART, /* other 7 bytes of register spill */
+ STACK_MISC /* BPF program wrote some data into this slot */
+};
+
+struct bpf_stack_slot {
+ enum bpf_stack_slot_type type;
+ enum bpf_reg_type ptr;
+ int imm;
+};
+
+/* state of the program:
+ * type of all registers and stack info
+ */
+struct verifier_state {
+ struct reg_state regs[MAX_BPF_REG];
+ struct bpf_stack_slot stack[MAX_BPF_STACK];
+};
+
+/* linked list of verifier states used to prune search */
+struct verifier_state_list {
+ struct verifier_state state;
+ struct verifier_state_list *next;
+};
+
+/* verifier_state + insn_idx are pushed to stack when branch is encountered */
+struct verifier_stack_elem {
+ /* verifer state is 'st'
+ * before processing instruction 'insn_idx'
+ * and after processing instruction 'prev_insn_idx'
+ */
+ struct verifier_state st;
+ int insn_idx;
+ int prev_insn_idx;
+ struct verifier_stack_elem *next;
+};
+
+#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
+
+/* single container for all structs
+ * one verifier_env per bpf_check() call
+ */
+struct verifier_env {
+ struct sk_filter *prog; /* eBPF program being verified */
+ struct verifier_stack_elem *head; /* stack of verifier states to be processed */
+ int stack_size; /* number of states to be processed */
+ struct verifier_state cur_state; /* current verifier state */
+ struct verifier_state_list **branch_landing; /* search prunning optimization */
+ u32 used_maps[MAX_USED_MAPS]; /* array of map_id's used by eBPF program */
+ u32 used_map_cnt; /* number of used maps */
+};
+
+/* verbose verifier prints what it's seeing
+ * bpf_check() is called under map lock, so no race to access this global var
+ */
+static bool verbose_on;
+
+/* when verifier rejects eBPF program, it does a second path with verbose on
+ * to dump the verification trace to the log, so the user can figure out what's
+ * wrong with the program
+ */
+static int verbose(const char *fmt, ...)
+{
+ va_list args;
+ int ret;
+
+ if (!verbose_on)
+ return 0;
+
+ va_start(args, fmt);
+ ret = vprintk(fmt, args);
+ va_end(args);
+ return ret;
+}
+
+/* string representation of 'enum bpf_reg_type' */
+static const char * const reg_type_str[] = {
+ [INVALID_PTR] = "inv",
+ [PTR_TO_CTX] = "ctx",
+ [PTR_TO_MAP] = "map_value",
+ [PTR_TO_MAP_CONDITIONAL] = "map_value_or_null",
+ [PTR_TO_STACK] = "fp",
+ [PTR_TO_STACK_IMM] = "fp",
+ [PTR_TO_STACK_IMM_MAP_KEY] = "fp_key",
+ [PTR_TO_STACK_IMM_MAP_VALUE] = "fp_value",
+ [RET_INTEGER] = "ret_int",
+ [RET_VOID] = "ret_void",
+ [CONST_ARG] = "imm",
+ [CONST_ARG_MAP_ID] = "map_id",
+ [CONST_ARG_STACK_IMM_SIZE] = "imm_size",
+};
+
+static void pr_cont_verifier_state(struct verifier_env *env)
+{
+ enum bpf_reg_type ptr;
+ int i;
+
+ for (i = 0; i < MAX_BPF_REG; i++) {
+ if (!env->cur_state.regs[i].read_ok)
+ continue;
+ ptr = env->cur_state.regs[i].ptr;
+ pr_cont(" R%d=%s", i, reg_type_str[ptr]);
+ if (ptr == CONST_ARG ||
+ ptr == PTR_TO_STACK_IMM ||
+ ptr == PTR_TO_MAP_CONDITIONAL ||
+ ptr == PTR_TO_MAP)
+ pr_cont("%d", env->cur_state.regs[i].imm);
+ }
+ for (i = 0; i < MAX_BPF_STACK; i++) {
+ if (env->cur_state.stack[i].type == STACK_SPILL)
+ pr_cont(" fp%d=%s", -MAX_BPF_STACK + i,
+ reg_type_str[env->cur_state.stack[i].ptr]);
+ }
+ pr_cont("\n");
+}
+
+static const char *const bpf_class_string[] = {
+ "ld", "ldx", "st", "stx", "alu", "jmp", "BUG", "alu64"
+};
+
+static const char *const bpf_alu_string[] = {
+ "+=", "-=", "*=", "/=", "|=", "&=", "<<=", ">>=", "neg",
+ "%=", "^=", "=", "s>>=", "endian", "BUG", "BUG"
+};
+
+static const char *const bpf_ldst_string[] = {
+ "u32", "u16", "u8", "u64"
+};
+
+static const char *const bpf_jmp_string[] = {
+ "jmp", "==", ">", ">=", "&", "!=", "s>", "s>=", "call", "exit"
+};
+
+static void pr_cont_bpf_insn(struct sock_filter_int *insn)
+{
+ u8 class = BPF_CLASS(insn->code);
+
+ if (class == BPF_ALU || class == BPF_ALU64) {
+ if (BPF_SRC(insn->code) == BPF_X)
+ pr_cont("(%02x) %sr%d %s %sr%d\n",
+ insn->code, class == BPF_ALU ? "(u32) " : "",
+ insn->dst_reg,
+ bpf_alu_string[BPF_OP(insn->code) >> 4],
+ class == BPF_ALU ? "(u32) " : "",
+ insn->src_reg);
+ else
+ pr_cont("(%02x) %sr%d %s %s%d\n",
+ insn->code, class == BPF_ALU ? "(u32) " : "",
+ insn->dst_reg,
+ bpf_alu_string[BPF_OP(insn->code) >> 4],
+ class == BPF_ALU ? "(u32) " : "",
+ insn->imm);
+ } else if (class == BPF_STX) {
+ if (BPF_MODE(insn->code) == BPF_MEM)
+ pr_cont("(%02x) *(%s *)(r%d %+d) = r%d\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->dst_reg,
+ insn->off, insn->src_reg);
+ else if (BPF_MODE(insn->code) == BPF_XADD)
+ pr_cont("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->dst_reg, insn->off,
+ insn->src_reg);
+ else
+ pr_cont("BUG_%02x\n", insn->code);
+ } else if (class == BPF_ST) {
+ if (BPF_MODE(insn->code) != BPF_MEM) {
+ pr_cont("BUG_st_%02x\n", insn->code);
+ return;
+ }
+ pr_cont("(%02x) *(%s *)(r%d %+d) = %d\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->dst_reg,
+ insn->off, insn->imm);
+ } else if (class == BPF_LDX) {
+ if (BPF_MODE(insn->code) != BPF_MEM) {
+ pr_cont("BUG_ldx_%02x\n", insn->code);
+ return;
+ }
+ pr_cont("(%02x) r%d = *(%s *)(r%d %+d)\n",
+ insn->code, insn->dst_reg,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->src_reg, insn->off);Can you please add:
+ } else if (class == BPF_LD) {
+ if (BPF_MODE(insn->code) == BPF_ABS) {
+ pr_cont("(%02x) r0 = *(%s *)skb[%d]\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->imm);
+ } else if (BPF_MODE(insn->code) == BPF_IND) {
+ pr_cont("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->src_reg, insn->imm);
+ } else {
+ pr_cont("BUG_ld_%02x\n", insn->code);
+ return;
+ }
Note that I'm hardcoding r0 (instead of using %d for insn->dst_reg)
because that's how ebpf writes the instructions.
+ } else if (class == BPF_JMP) {
+ u8 opcode = BPF_OP(insn->code);
+
+ if (opcode == BPF_CALL) {
+ pr_cont("(%02x) call %d\n", insn->code, insn->imm);
+ } else if (insn->code == (BPF_JMP | BPF_JA)) {
+ pr_cont("(%02x) goto pc%+d\n",
+ insn->code, insn->off);
+ } else if (insn->code == (BPF_JMP | BPF_EXIT)) {
+ pr_cont("(%02x) exit\n", insn->code);
+ } else if (BPF_SRC(insn->code) == BPF_X) {
+ pr_cont("(%02x) if r%d %s r%d goto pc%+d\n",
+ insn->code, insn->dst_reg,
+ bpf_jmp_string[BPF_OP(insn->code) >> 4],
+ insn->src_reg, insn->off);
+ } else {
+ pr_cont("(%02x) if r%d %s 0x%x goto pc%+d\n",
+ insn->code, insn->dst_reg,
+ bpf_jmp_string[BPF_OP(insn->code) >> 4],
+ insn->imm, insn->off);
+ }
+ } else {
+ pr_cont("(%02x) %s\n", insn->code, bpf_class_string[class]);
+ }
+}
+
+static int pop_stack(struct verifier_env *env, int *prev_insn_idx)
+{
+ struct verifier_stack_elem *elem;
+ int insn_idx;
+
+ if (env->head == NULL)
+ return -1;
+
+ memcpy(&env->cur_state, &env->head->st, sizeof(env->cur_state));
+ insn_idx = env->head->insn_idx;
+ if (prev_insn_idx)
+ *prev_insn_idx = env->head->prev_insn_idx;
+ elem = env->head->next;
+ kfree(env->head);
+ env->head = elem;
+ env->stack_size--;
+ return insn_idx;
+}
+
+static struct verifier_state *push_stack(struct verifier_env *env, int insn_idx,
+ int prev_insn_idx)
+{
+ struct verifier_stack_elem *elem;
+
+ elem = kmalloc(sizeof(struct verifier_stack_elem), GFP_KERNEL);
+ if (!elem)
+ goto err;
+
+ memcpy(&elem->st, &env->cur_state, sizeof(env->cur_state));
+ elem->insn_idx = insn_idx;
+ elem->prev_insn_idx = prev_insn_idx;
+ elem->next = env->head;
+ env->head = elem;
+ env->stack_size++;
+ if (env->stack_size > 1024) {
+ verbose("BPF program is too complex\n");
+ goto err;
+ }
+ return &elem->st;
+err:
+ /* pop all elements and return */
+ while (pop_stack(env, NULL) >= 0);
+ return NULL;
+}
+
+#define CALLER_SAVED_REGS 6
+static const int caller_saved[CALLER_SAVED_REGS] = {
+ BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
+};
+
+static void init_reg_state(struct reg_state *regs)
+{
+ struct reg_state *reg;
+ int i;
+
+ for (i = 0; i < MAX_BPF_REG; i++) {
+ regs[i].ptr = INVALID_PTR;
+ regs[i].read_ok = false;
+ regs[i].imm = 0xbadbad;
+ }
+ reg = regs + BPF_REG_FP;Any reason you switching from the array syntax to the pointer one? I find "reg = regs[BPF_REG_FP];" more readable (and the one you chose in the loop).
+ reg->ptr = PTR_TO_STACK; + reg->read_ok = true; + + reg = regs + BPF_REG_1; /* 1st arg to a function */ + reg->ptr = PTR_TO_CTX;
Wait, doesn't this depend on doing "BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1)" (the bpf-to-ebpf prologue), which is only enforced on filters converted from bpf? In fact, shouldn't this set regs[BPF_REG_CTX] instead of regs[BPF_REG_1] ?
+ reg->read_ok = true;
+}
+
+static void mark_reg_no_ptr(struct reg_state *regs, int regno)
+{
+ regs[regno].ptr = INVALID_PTR;
+ regs[regno].imm = 0xbadbad;
+ regs[regno].read_ok = true;
+}
+
+static int check_reg_arg(struct reg_state *regs, int regno, bool is_src)
+{
+ if (is_src) {
+ if (!regs[regno].read_ok) {
+ verbose("R%d !read_ok\n", regno);
+ return -EACCES;
+ }
+ } else {
+ if (regno == BPF_REG_FP)
+ /* frame pointer is read only */
+ return -EACCES;
+ mark_reg_no_ptr(regs, regno);
+ }
+ return 0;
+}
+
+static int bpf_size_to_bytes(int bpf_size)
+{
+ if (bpf_size == BPF_W)
+ return 4;
+ else if (bpf_size == BPF_H)
+ return 2;
+ else if (bpf_size == BPF_B)
+ return 1;
+ else if (bpf_size == BPF_DW)
+ return 8;
+ else
+ return -EACCES;
+}
+
+static int check_stack_write(struct verifier_state *state, int off, int size,
+ int value_regno)
+{
+ struct bpf_stack_slot *slot;
+ int i;
+
+ if (value_regno >= 0 &&
+ (state->regs[value_regno].ptr == PTR_TO_MAP ||
+ state->regs[value_regno].ptr == PTR_TO_STACK_IMM ||
+ state->regs[value_regno].ptr == PTR_TO_CTX)) {
+
+ /* register containing pointer is being spilled into stack */
+ if (size != 8) {
+ verbose("invalid size of register spill\n");
+ return -EACCES;
+ }
+
+ slot = &state->stack[MAX_BPF_STACK + off];
+ slot->type = STACK_SPILL;
+ /* save register state */
+ slot->ptr = state->regs[value_regno].ptr;
+ slot->imm = state->regs[value_regno].imm;
+ for (i = 1; i < 8; i++) {
+ slot = &state->stack[MAX_BPF_STACK + off + i];
+ slot->type = STACK_SPILL_PART;
+ slot->ptr = 0;
+ slot->imm = 0;
+ }
+ } else {
+
+ /* regular write of data into stack */
+ for (i = 0; i < size; i++) {
+ slot = &state->stack[MAX_BPF_STACK + off + i];
+ slot->type = STACK_MISC;
+ slot->ptr = 0;
+ slot->imm = 0;
+ }
+ }
+ return 0;
+}
+
+static int check_stack_read(struct verifier_state *state, int off, int size,
+ int value_regno)
+{
+ int i;
+ struct bpf_stack_slot *slot;
+
+ slot = &state->stack[MAX_BPF_STACK + off];
+
+ if (slot->type == STACK_SPILL) {
+ if (size != 8) {
+ verbose("invalid size of register spill\n");
+ return -EACCES;
+ }
+ for (i = 1; i < 8; i++) {
+ if (state->stack[MAX_BPF_STACK + off + i].type !=
+ STACK_SPILL_PART) {
+ verbose("corrupted spill memory\n");
+ return -EACCES;
+ }
+ }
+
+ /* restore register state from stack */
+ state->regs[value_regno].ptr = slot->ptr;
+ state->regs[value_regno].imm = slot->imm;
+ state->regs[value_regno].read_ok = true;
+ return 0;
+ } else {
+ for (i = 0; i < size; i++) {
+ if (state->stack[MAX_BPF_STACK + off + i].type !=
+ STACK_MISC) {
+ verbose("invalid read from stack off %d+%d size %d\n",
+ off, i, size);
+ return -EACCES;
+ }
+ }
+ /* have read misc data from the stack */
+ mark_reg_no_ptr(state->regs, value_regno);
+ return 0;
+ }
+}
+
+static int remember_map_id(struct verifier_env *env, u32 map_id)
+{
+ int i;
+
+ /* check whether we recorded this map_id already */
+ for (i = 0; i < env->used_map_cnt; i++)
+ if (env->used_maps[i] == map_id)
+ return 0;
+
+ if (env->used_map_cnt >= MAX_USED_MAPS)
+ return -E2BIG;
+
+ /* remember this map_id */
+ env->used_maps[env->used_map_cnt++] = map_id;
+ return 0;
+}
+
+static int get_map_info(struct verifier_env *env, u32 map_id,
+ struct bpf_map **map)
+{
+ /* if BPF program contains bpf_table_lookup(map_id, key)
+ * the incorrect map_id will be caught here
+ */
+ *map = bpf_map_get(map_id);
+ if (!*map) {
+ verbose("invalid access to map_id=%d\n", map_id);
+ return -EACCES;
+ }
+
+ _(remember_map_id(env, map_id));
+
+ return 0;
+}
+
+/* check read/write into map element returned by bpf_table_lookup() */
+static int check_table_access(struct verifier_env *env, int regno, int off,
+ int size)
+{
+ struct bpf_map *map;
+ int map_id = env->cur_state.regs[regno].imm;
+
+ _(get_map_info(env, map_id, &map));
+
+ if (off < 0 || off + size > map->value_size) {
+ verbose("invalid access to map_id=%d leaf_size=%d off=%d size=%d\n",
+ map_id, map->value_size, off, size);
+ return -EACCES;
+ }
+ return 0;
+}
+
+/* check access to 'struct bpf_context' fields */
+static int check_ctx_access(struct verifier_env *env, int off, int size,
+ enum bpf_access_type t)
+{
+ if (env->prog->info->ops->is_valid_access &&
+ env->prog->info->ops->is_valid_access(off, size, t))
+ return 0;
+
+ verbose("invalid bpf_context access off=%d size=%d\n", off, size);
+ return -EACCES;
+}
+
+static int check_mem_access(struct verifier_env *env, int regno, int off,
+ int bpf_size, enum bpf_access_type t,
+ int value_regno)
+{
+ struct verifier_state *state = &env->cur_state;
+ int size;
+
+ _(size = bpf_size_to_bytes(bpf_size));
+
+ if (off % size != 0) {
+ verbose("misaligned access off %d size %d\n", off, size);
+ return -EACCES;
+ }
+
+ if (state->regs[regno].ptr == PTR_TO_MAP) {
+ _(check_table_access(env, regno, off, size));
+ if (t == BPF_READ)
+ mark_reg_no_ptr(state->regs, value_regno);
+ } else if (state->regs[regno].ptr == PTR_TO_CTX) {
+ _(check_ctx_access(env, off, size, t));
+ if (t == BPF_READ)
+ mark_reg_no_ptr(state->regs, value_regno);
+ } else if (state->regs[regno].ptr == PTR_TO_STACK) {
+ if (off >= 0 || off < -MAX_BPF_STACK) {
+ verbose("invalid stack off=%d size=%d\n", off, size);
+ return -EACCES;
+ }
+ if (t == BPF_WRITE)
+ _(check_stack_write(state, off, size, value_regno));
+ else
+ _(check_stack_read(state, off, size, value_regno));
+ } else {
+ verbose("R%d invalid mem access '%s'\n",
+ regno, reg_type_str[state->regs[regno].ptr]);
+ return -EACCES;
+ }
+ return 0;
+}
+
+/* when register 'regno' is passed into function that will read 'access_size'
+ * bytes from that pointer, make sure that it's within stack boundary
+ * and all elements of stack are initialized
+ */
+static int check_stack_boundary(struct verifier_env *env,
+ int regno, int access_size)
+{
+ struct verifier_state *state = &env->cur_state;
+ struct reg_state *regs = state->regs;
+ int off, i;
+
+ if (regs[regno].ptr != PTR_TO_STACK_IMM)
+ return -EACCES;
+
+ off = regs[regno].imm;
+ if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
+ access_size <= 0) {
+ verbose("invalid stack ptr R%d off=%d access_size=%d\n",
+ regno, off, access_size);
+ return -EACCES;
+ }
+
+ for (i = 0; i < access_size; i++) {
+ if (state->stack[MAX_BPF_STACK + off + i].type != STACK_MISC) {
+ verbose("invalid indirect read from stack off %d+%d size %d\n",
+ off, i, access_size);
+ return -EACCES;
+ }
+ }
+ return 0;
+}
+
+static int check_func_arg(struct verifier_env *env, int regno,
+ enum bpf_reg_type arg_type, int *map_id,
+ struct bpf_map **mapp)
+{
+ struct reg_state *reg = env->cur_state.regs + regno;
+ enum bpf_reg_type expected_type;
+
+ if (arg_type == INVALID_PTR)
+ return 0;
+
+ if (!reg->read_ok) {
+ verbose("R%d !read_ok\n", regno);
+ return -EACCES;
+ }
+
+ if (arg_type == PTR_TO_STACK_IMM_MAP_KEY ||
+ arg_type == PTR_TO_STACK_IMM_MAP_VALUE)
+ expected_type = PTR_TO_STACK_IMM;
+ else if (arg_type == CONST_ARG_MAP_ID ||
+ arg_type == CONST_ARG_STACK_IMM_SIZE)
+ expected_type = CONST_ARG;
+ else
+ expected_type = arg_type;
+
+ if (reg->ptr != expected_type) {
+ verbose("R%d type=%s expected=%s\n", regno,
+ reg_type_str[reg->ptr], reg_type_str[expected_type]);
+ return -EACCES;
+ }
+
+ if (arg_type == CONST_ARG_MAP_ID) {
+ /* bpf_map_xxx(map_id) call: check that map_id is valid */
+ *map_id = reg->imm;
+ _(get_map_info(env, reg->imm, mapp));
+ } else if (arg_type == PTR_TO_STACK_IMM_MAP_KEY) {
+ /*
+ * bpf_map_xxx(..., map_id, ..., key) call:
+ * check that [key, key + map->key_size) are within
+ * stack limits and initialized
+ */
+ if (!*mapp) {
+ /*
+ * in function declaration map_id must come before
+ * table_key or table_elem, so that it's verified
+ * and known before we have to check table_key here
+ */
+ verbose("invalid map_id to access map->key\n");
+ return -EACCES;
+ }
+ _(check_stack_boundary(env, regno, (*mapp)->key_size));
+ } else if (arg_type == PTR_TO_STACK_IMM_MAP_VALUE) {
+ /*
+ * bpf_map_xxx(..., map_id, ..., value) call:
+ * check [value, value + map->value_size) validity
+ */
+ if (!*mapp) {
+ verbose("invalid map_id to access map->elem\n");
+ return -EACCES;
+ }
+ _(check_stack_boundary(env, regno, (*mapp)->value_size));
+ } else if (arg_type == CONST_ARG_STACK_IMM_SIZE) {
+ /*
+ * bpf_xxx(..., buf, len) call will access 'len' bytes
+ * from stack pointer 'buf'. Check it
+ * note: regno == len, regno - 1 == buf
+ */
+ _(check_stack_boundary(env, regno - 1, reg->imm));
+ }
+
+ return 0;
+}
+
+static int check_call(struct verifier_env *env, int func_id)
+{
+ struct verifier_state *state = &env->cur_state;
+ const struct bpf_func_proto *fn = NULL;
+ struct reg_state *regs = state->regs;
+ struct bpf_map *map = NULL;
+ struct reg_state *reg;
+ int map_id = -1;
+ int i;
+
+ /* find function prototype */
+ if (func_id <= 0 || func_id >= __BPF_FUNC_MAX_ID) {
+ verbose("invalid func %d\n", func_id);
+ return -EINVAL;
+ }
+
+ if (env->prog->info->ops->get_func_proto)
+ fn = env->prog->info->ops->get_func_proto(func_id);
+
+ if (!fn || (fn->ret_type != RET_INTEGER &&
+ fn->ret_type != PTR_TO_MAP_CONDITIONAL &&
+ fn->ret_type != RET_VOID)) {
+ verbose("unknown func %d\n", func_id);
+ return -EINVAL;
+ }
+
+ /* check args */
+ _(check_func_arg(env, BPF_REG_1, fn->arg1_type, &map_id, &map));
+ _(check_func_arg(env, BPF_REG_2, fn->arg2_type, &map_id, &map));
+ _(check_func_arg(env, BPF_REG_3, fn->arg3_type, &map_id, &map));
+ _(check_func_arg(env, BPF_REG_4, fn->arg4_type, &map_id, &map));
+
+ /* reset caller saved regs */
+ for (i = 0; i < CALLER_SAVED_REGS; i++) {
+ reg = regs + caller_saved[i];
+ reg->read_ok = false;
+ reg->ptr = INVALID_PTR;
+ reg->imm = 0xbadbad;
+ }
+
+ /* update return register */
+ reg = regs + BPF_REG_0;
+ if (fn->ret_type == RET_INTEGER) {
+ reg->read_ok = true;
+ reg->ptr = INVALID_PTR;
+ } else if (fn->ret_type != RET_VOID) {
+ reg->read_ok = true;
+ reg->ptr = fn->ret_type;
+ if (fn->ret_type == PTR_TO_MAP_CONDITIONAL)
+ /*
+ * remember map_id, so that check_table_access()
+ * can check 'value_size' boundary of memory access
+ * to map element returned from bpf_table_lookup()
+ */
+ reg->imm = map_id;
+ }
+ return 0;
+}
+
+/* check validity of 32-bit and 64-bit arithmetic operations */
+static int check_alu_op(struct reg_state *regs, struct sock_filter_int *insn)
+{
+ u8 opcode = BPF_OP(insn->code);
+
+ if (opcode == BPF_END || opcode == BPF_NEG) {
+ if (BPF_SRC(insn->code) != BPF_X)
+ return -EINVAL;
+ /* check src operand */
+ _(check_reg_arg(regs, insn->dst_reg, 1));
+
+ /* check dest operand */
+ _(check_reg_arg(regs, insn->dst_reg, 0));
+
+ } else if (opcode == BPF_MOV) {
+
+ if (BPF_SRC(insn->code) == BPF_X)
+ /* check src operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+
+ /* check dest operand */
+ _(check_reg_arg(regs, insn->dst_reg, 0));
+
+ if (BPF_SRC(insn->code) == BPF_X) {
+ if (BPF_CLASS(insn->code) == BPF_ALU64) {
+ /* case: R1 = R2
+ * copy register state to dest reg
+ */
+ regs[insn->dst_reg].ptr = regs[insn->src_reg].ptr;
+ regs[insn->dst_reg].imm = regs[insn->src_reg].imm;
+ } else {
+ regs[insn->dst_reg].ptr = INVALID_PTR;
+ regs[insn->dst_reg].imm = 0;
+ }
+ } else {
+ /* case: R = imm
+ * remember the value we stored into this reg
+ */
+ regs[insn->dst_reg].ptr = CONST_ARG;
+ regs[insn->dst_reg].imm = insn->imm;
+ }
+
+ } else { /* all other ALU ops: and, sub, xor, add, ... */
+
+ int stack_relative = 0;
+
+ if (BPF_SRC(insn->code) == BPF_X)
+ /* check src1 operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+
+ /* check src2 operand */
+ _(check_reg_arg(regs, insn->dst_reg, 1));
+
+ if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
+ regs[insn->dst_reg].ptr == PTR_TO_STACK &&
+ BPF_SRC(insn->code) == BPF_K)
+ stack_relative = 1;
+
+ /* check dest operand */
+ _(check_reg_arg(regs, insn->dst_reg, 0));
+
+ if (stack_relative) {
+ regs[insn->dst_reg].ptr = PTR_TO_STACK_IMM;
+ regs[insn->dst_reg].imm = insn->imm;
+ }
+ }
+
+ return 0;
+}
+
+static int check_cond_jmp_op(struct verifier_env *env,
+ struct sock_filter_int *insn, int *insn_idx)
+{
+ struct reg_state *regs = env->cur_state.regs;
+ struct verifier_state *other_branch;
+ u8 opcode = BPF_OP(insn->code);
+
+ if (BPF_SRC(insn->code) == BPF_X)
+ /* check src1 operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+
+ /* check src2 operand */
+ _(check_reg_arg(regs, insn->dst_reg, 1));
+
+ /* detect if R == 0 where R was initialized to zero earlier */
+ if (BPF_SRC(insn->code) == BPF_K &&
+ (opcode == BPF_JEQ || opcode == BPF_JNE) &&
+ regs[insn->dst_reg].ptr == CONST_ARG &&
+ regs[insn->dst_reg].imm == insn->imm) {
+ if (opcode == BPF_JEQ) {
+ /* if (imm == imm) goto pc+off;
+ * only follow the goto, ignore fall-through
+ */
+ *insn_idx += insn->off;
+ return 0;
+ } else {
+ /* if (imm != imm) goto pc+off;
+ * only follow fall-through branch, since
+ * that's where the program will go
+ */
+ return 0;
+ }
+ }
+
+ other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
+ if (!other_branch)
+ return -EFAULT;
+
+ /* detect if R == 0 where R is returned value from table_lookup() */
+ if (BPF_SRC(insn->code) == BPF_K &&
+ insn->imm == 0 && (opcode == BPF_JEQ ||
+ opcode == BPF_JNE) &&
+ regs[insn->dst_reg].ptr == PTR_TO_MAP_CONDITIONAL) {
+ if (opcode == BPF_JEQ) {
+ /* next fallthrough insn can access memory via
+ * this register
+ */
+ regs[insn->dst_reg].ptr = PTR_TO_MAP;
+ /* branch targer cannot access it, since reg == 0 */
+ other_branch->regs[insn->dst_reg].ptr = CONST_ARG;
+ other_branch->regs[insn->dst_reg].imm = 0;
+ } else {
+ other_branch->regs[insn->dst_reg].ptr = PTR_TO_MAP;
+ regs[insn->dst_reg].ptr = CONST_ARG;
+ regs[insn->dst_reg].imm = 0;
+ }
+ } else if (BPF_SRC(insn->code) == BPF_K &&
+ (opcode == BPF_JEQ || opcode == BPF_JNE)) {
+
+ if (opcode == BPF_JEQ) {
+ /* detect if (R == imm) goto
+ * and in the target state recognize that R = imm
+ */
+ other_branch->regs[insn->dst_reg].ptr = CONST_ARG;
+ other_branch->regs[insn->dst_reg].imm = insn->imm;
+ } else {
+ /* detect if (R != imm) goto
+ * and in the fall-through state recognize that R = imm
+ */
+ regs[insn->dst_reg].ptr = CONST_ARG;
+ regs[insn->dst_reg].imm = insn->imm;
+ }
+ }
+ if (verbose_on)
+ pr_cont_verifier_state(env);
+ return 0;
+}
+
+/* verify safety of LD_ABS|LD_IND instructions:
+ * - they can only appear in the programs where ctx == skb
+ * - since they are wrappers of function calls, they scratch R1-R5 registers,
+ * preserve R6-R9, and store return value into R0
+ *
+ * Implicit input:
+ * ctx == skb == R6 == CTX
+ *
+ * Explicit input:
+ * SRC == any register
+ * IMM == 32-bit immediate
+ *
+ * Output:
+ * R0 - 8/16/32-bit skb data converted to cpu endianness
+ */
+
+static int check_ld_abs(struct verifier_env *env, struct sock_filter_int *insn)
+{
+ struct reg_state *regs = env->cur_state.regs;
+ u8 mode = BPF_MODE(insn->code);
+ struct reg_state *reg;
+ int i;
+
+ if (mode != BPF_ABS && mode != BPF_IND)
+ return -EINVAL;
+
+ if (env->prog->info->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) {
+ verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n");
+ return -EINVAL;
+ }
+
+ /* check whether implicit source operand (register R6) is readable */
+ _(check_reg_arg(regs, BPF_REG_6, 1));
+
+ if (regs[BPF_REG_6].ptr != PTR_TO_CTX) {
+ verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
+ return -EINVAL;
+ }
+
+ if (mode == BPF_IND)
+ /* check explicit source operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+
+ /* reset caller saved regs to unreadable */
+ for (i = 0; i < CALLER_SAVED_REGS; i++) {
+ reg = regs + caller_saved[i];
+ reg->read_ok = false;
+ reg->ptr = INVALID_PTR;
+ reg->imm = 0xbadbad;
+ }
+
+ /* mark destination R0 register as readable, since it contains
+ * the value fetched from the packet
+ */
+ regs[BPF_REG_0].read_ok = true;
+ return 0;
+}
+
+/* non-recursive DFS pseudo code
+ * 1 procedure DFS-iterative(G,v):
+ * 2 label v as discovered
+ * 3 let S be a stack
+ * 4 S.push(v)
+ * 5 while S is not empty
+ * 6 t <- S.pop()
+ * 7 if t is what we're looking for:
+ * 8 return t
+ * 9 for all edges e in G.adjacentEdges(t) do
+ * 10 if edge e is already labelled
+ * 11 continue with the next edge
+ * 12 w <- G.adjacentVertex(t,e)
+ * 13 if vertex w is not discovered and not explored
+ * 14 label e as tree-edge
+ * 15 label w as discovered
+ * 16 S.push(w)
+ * 17 continue at 5
+ * 18 else if vertex w is discovered
+ * 19 label e as back-edge
+ * 20 else
+ * 21 // vertex w is explored
+ * 22 label e as forward- or cross-edge
+ * 23 label t as explored
+ * 24 S.pop()
+ *
+ * convention:
+ * 1 - discovered
+ * 2 - discovered and 1st branch labelled
+ * 3 - discovered and 1st and 2nd branch labelled
+ * 4 - explored
+ */
+
+#define STATE_END ((struct verifier_state_list *)-1)
+
+#define PUSH_INT(I) \
+ do { \
+ if (cur_stack >= insn_cnt) { \
+ ret = -E2BIG; \
+ goto free_st; \
+ } \
+ stack[cur_stack++] = I; \
+ } while (0)
+
+#define PEAK_INT() \
+ ({ \
+ int _ret; \
+ if (cur_stack == 0) \
+ _ret = -1; \
+ else \
+ _ret = stack[cur_stack - 1]; \
+ _ret; \
+ })
+
+#define POP_INT() \
+ ({ \
+ int _ret; \
+ if (cur_stack == 0) \
+ _ret = -1; \
+ else \
+ _ret = stack[--cur_stack]; \
+ _ret; \
+ })
+
+#define PUSH_INSN(T, W, E) \
+ do { \
+ int w = W; \
+ if (E == 1 && st[T] >= 2) \
+ break; \
+ if (E == 2 && st[T] >= 3) \
+ break; \
+ if (w >= insn_cnt) { \
+ ret = -EACCES; \
+ goto free_st; \
+ } \
+ if (E == 2) \
+ /* mark branch target for state pruning */ \
+ env->branch_landing[w] = STATE_END; \
+ if (st[w] == 0) { \
+ /* tree-edge */ \
+ st[T] = 1 + E; \
+ st[w] = 1; /* discovered */ \
+ PUSH_INT(w); \
+ goto peak_stack; \
+ } else if (st[w] == 1 || st[w] == 2 || st[w] == 3) { \
+ verbose("back-edge from insn %d to %d\n", t, w); \
+ ret = -EINVAL; \
+ goto free_st; \
+ } else if (st[w] == 4) { \
+ /* forward- or cross-edge */ \
+ st[T] = 1 + E; \
+ } else { \
+ verbose("insn state internal bug\n"); \
+ ret = -EFAULT; \
+ goto free_st; \
+ } \
+ } while (0)
+
+/* non-recursive depth-first-search to detect loops in BPF program
+ * loop == back-edge in directed graph
+ */
+static int check_cfg(struct verifier_env *env)
+{
+ struct sock_filter_int *insns = env->prog->insnsi;
+ int insn_cnt = env->prog->len;
+ int cur_stack = 0;
+ int *stack;
+ int ret = 0;
+ int *st;
+ int i, t;
+
+ if (insns[insn_cnt - 1].code != (BPF_JMP | BPF_EXIT)) {
+ verbose("last insn is not a 'ret'\n");
+ return -EINVAL;
+ }
+
+ st = kzalloc(sizeof(int) * insn_cnt, GFP_KERNEL);
+ if (!st)
+ return -ENOMEM;
+
+ stack = kzalloc(sizeof(int) * insn_cnt, GFP_KERNEL);
+ if (!stack) {
+ kfree(st);
+ return -ENOMEM;
+ }
+
+ st[0] = 1; /* mark 1st insn as discovered */
+ PUSH_INT(0);
+
+peak_stack:
+ while ((t = PEAK_INT()) != -1) {
+ if (insns[t].code == (BPF_JMP | BPF_EXIT))
+ goto mark_explored;
+
+ if (BPF_CLASS(insns[t].code) == BPF_JMP) {
+ u8 opcode = BPF_OP(insns[t].code);
+
+ if (opcode == BPF_CALL) {
+ PUSH_INSN(t, t + 1, 1);
+ } else if (opcode == BPF_JA) {
+ if (BPF_SRC(insns[t].code) != BPF_X) {
+ ret = -EINVAL;
+ goto free_st;
+ }
+ PUSH_INSN(t, t + insns[t].off + 1, 1);
+ } else {
+ PUSH_INSN(t, t + 1, 1);
+ PUSH_INSN(t, t + insns[t].off + 1, 2);
+ }
+ /* tell verifier to check for equivalent verifier states
+ * after every call and jump
+ */
+ env->branch_landing[t + 1] = STATE_END;
+ } else {
+ PUSH_INSN(t, t + 1, 1);
+ }
+
+mark_explored:
+ st[t] = 4; /* explored */
+ if (POP_INT() == -1) {
+ verbose("pop_int internal bug\n");
+ ret = -EFAULT;
+ goto free_st;
+ }
+ }
+
+
+ for (i = 0; i < insn_cnt; i++) {
+ if (st[i] != 4) {
+ verbose("unreachable insn %d\n", i);
+ ret = -EINVAL;
+ goto free_st;
+ }
+ }
+
+free_st:
+ kfree(st);
+ kfree(stack);
+ return ret;
+}
+
+/* compare two verifier states
+ *
+ * all states stored in state_list are known to be valid, since
+ * verifier reached 'bpf_exit' instruction through them
+ *
+ * this function is called when verifier exploring different branches of
+ * execution popped from the state stack. If it sees an old state that has
+ * more strict register state and more strict stack state then this execution
+ * branch doesn't need to be explored further, since verifier already
+ * concluded that more strict state leads to valid finish.
+ *
+ * Therefore two states are equivalent if register state is more conservative
+ * and explored stack state is more conservative than the current one.
+ * Example:
+ * explored current
+ * (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
+ * (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
+ *
+ * In other words if current stack state (one being explored) has more
+ * valid slots than old one that already passed validation, it means
+ * the verifier can stop exploring and conclude that current state is valid too
+ *
+ * Similarly with registers. If explored state has register type as invalid
+ * whereas register type in current state is meaningful, it means that
+ * the current state will reach 'bpf_exit' instruction safely
+ */
+static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
+{
+ int i;
+
+ for (i = 0; i < MAX_BPF_REG; i++) {
+ if (memcmp(&old->regs[i], &cur->regs[i],
+ sizeof(old->regs[0])) != 0) {
+ if (!old->regs[i].read_ok)
+ continue;
+ if (old->regs[i].ptr == INVALID_PTR)
+ continue;
+ return false;
+ }
+ }
+
+ for (i = 0; i < MAX_BPF_STACK; i++) {
+ if (memcmp(&old->stack[i], &cur->stack[i],
+ sizeof(old->stack[0])) != 0) {
+ if (old->stack[i].type == STACK_INVALID)
+ continue;
+ return false;
+ }
+ }
+ return true;
+}
+
+static int is_state_visited(struct verifier_env *env, int insn_idx)
+{
+ struct verifier_state_list *new_sl;
+ struct verifier_state_list *sl;
+
+ sl = env->branch_landing[insn_idx];
+ if (!sl)
+ /* no branch jump to this insn, ignore it */
+ return 0;
+
+ while (sl != STATE_END) {
+ if (states_equal(&sl->state, &env->cur_state))
+ /* reached equivalent register/stack state,
+ * prune the search
+ */
+ return 1;
+ sl = sl->next;
+ }
+ new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_KERNEL);
+
+ if (!new_sl)
+ /* ignore ENOMEM, it doesn't affect correctness */
+ return 0;
+
+ /* add new state to the head of linked list */
+ memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
+ new_sl->next = env->branch_landing[insn_idx];
+ env->branch_landing[insn_idx] = new_sl;
+ return 0;
+}
+
+static int do_check(struct verifier_env *env)
+{
+ struct verifier_state *state = &env->cur_state;
+ struct sock_filter_int *insns = env->prog->insnsi;
+ struct reg_state *regs = state->regs;
+ int insn_cnt = env->prog->len;
+ int insn_idx, prev_insn_idx = 0;
+ int insn_processed = 0;
+ bool do_print_state = false;
+
+ init_reg_state(regs);
+ insn_idx = 0;
+ for (;;) {
+ struct sock_filter_int *insn;
+ u8 class;
+
+ if (insn_idx >= insn_cnt) {
+ verbose("invalid insn idx %d insn_cnt %d\n",
+ insn_idx, insn_cnt);
+ return -EFAULT;
+ }
+
+ insn = &insns[insn_idx];
+ class = BPF_CLASS(insn->code);
+
+ if (++insn_processed > 32768) {
+ verbose("BPF program is too large. Proccessed %d insn\n",
+ insn_processed);
+ return -E2BIG;
+ }
+
+ if (is_state_visited(env, insn_idx)) {
+ if (verbose_on) {
+ if (do_print_state)
+ pr_cont("\nfrom %d to %d: safe\n",
+ prev_insn_idx, insn_idx);
+ else
+ pr_cont("%d: safe\n", insn_idx);
+ }
+ goto process_bpf_exit;
+ }
+
+ if (verbose_on && do_print_state) {
+ pr_cont("\nfrom %d to %d:", prev_insn_idx, insn_idx);
+ pr_cont_verifier_state(env);
+ do_print_state = false;
+ }
+
+ if (verbose_on) {
+ pr_cont("%d: ", insn_idx);
+ pr_cont_bpf_insn(insn);
+ }
+
+ if (class == BPF_ALU || class == BPF_ALU64) {
+ _(check_alu_op(regs, insn));
+
+ } else if (class == BPF_LDX) {
+ if (BPF_MODE(insn->code) != BPF_MEM)
+ return -EINVAL;
+
+ /* check src operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+
+ _(check_mem_access(env, insn->src_reg, insn->off,
+ BPF_SIZE(insn->code), BPF_READ,
+ insn->dst_reg));
+
+ /* dest reg state will be updated by mem_access */
+
+ } else if (class == BPF_STX) {
+ /* check src1 operand */
+ _(check_reg_arg(regs, insn->src_reg, 1));
+ /* check src2 operand */
+ _(check_reg_arg(regs, insn->dst_reg, 1));
+ _(check_mem_access(env, insn->dst_reg, insn->off,
+ BPF_SIZE(insn->code), BPF_WRITE,
+ insn->src_reg));
+
+ } else if (class == BPF_ST) {
+ if (BPF_MODE(insn->code) != BPF_MEM)
+ return -EINVAL;
+ /* check src operand */
+ _(check_reg_arg(regs, insn->dst_reg, 1));
+ _(check_mem_access(env, insn->dst_reg, insn->off,
+ BPF_SIZE(insn->code), BPF_WRITE,
+ -1));
+
+ } else if (class == BPF_JMP) {
+ u8 opcode = BPF_OP(insn->code);
+
+ if (opcode == BPF_CALL) {
+ _(check_call(env, insn->imm));
+ } else if (opcode == BPF_JA) {
+ if (BPF_SRC(insn->code) != BPF_X)
+ return -EINVAL;
+ insn_idx += insn->off + 1;
+ continue;
+ } else if (opcode == BPF_EXIT) {
+ /* eBPF calling convetion is such that R0 is used
+ * to return the value from eBPF program.
+ * Make sure that it's readable at this time
+ * of bpf_exit, which means that program wrote
+ * something into it earlier
+ */
+ _(check_reg_arg(regs, BPF_REG_0, 1));
+process_bpf_exit:
+ insn_idx = pop_stack(env, &prev_insn_idx);
+ if (insn_idx < 0) {
+ break;
+ } else {
+ do_print_state = true;
+ continue;
+ }
+ } else {
+ _(check_cond_jmp_op(env, insn, &insn_idx));
+ }
+ } else if (class == BPF_LD) {
+ _(check_ld_abs(env, insn));
+ } else {
+ verbose("unknown insn class %d\n", class);
+ return -EINVAL;
+ }
+
+ insn_idx++;
+ }
+
+ return 0;
+}
+
+static void free_states(struct verifier_env *env, int insn_cnt)
+{
+ struct verifier_state_list *sl, *sln;
+ int i;
+
+ for (i = 0; i < insn_cnt; i++) {
+ sl = env->branch_landing[i];
+
+ if (sl)
+ while (sl != STATE_END) {
+ sln = sl->next;
+ kfree(sl);
+ sl = sln;
+ }
+ }
+
+ kfree(env->branch_landing);
+}
+
+int bpf_check(struct sk_filter *prog)
+{
+ struct verifier_env *env;
+ int ret;
+
+ if (prog->len <= 0 || prog->len > BPF_MAXINSNS)
+ return -E2BIG;
+
+ env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
+ if (!env)
+ return -ENOMEM;
+
+ verbose_on = false;
+retry:
+ env->prog = prog;
+ env->branch_landing = kcalloc(prog->len,
+ sizeof(struct verifier_state_list *),
+ GFP_KERNEL);
+
+ if (!env->branch_landing) {
+ kfree(env);
+ return -ENOMEM;
+ }
+
+ ret = check_cfg(env);
+ if (ret < 0)
+ goto free_env;
+
+ ret = do_check(env);
+
+free_env:
+ while (pop_stack(env, NULL) >= 0);
+ free_states(env, prog->len);
+
+ if (ret < 0 && !verbose_on && capable(CAP_SYS_ADMIN)) {
+ /* verification failed, redo it with verbose on */
+ memset(env, 0, sizeof(struct verifier_env));
+ verbose_on = true;
+ goto retry;
+ }
+
+ if (ret == 0 && env->used_map_cnt) {
+ /* if program passed verifier, update used_maps in bpf_prog_info */
+ prog->info->used_maps = kmalloc_array(env->used_map_cnt,
+ sizeof(u32), GFP_KERNEL);
+ if (!prog->info->used_maps) {
+ kfree(env);
+ return -ENOMEM;
+ }
+ memcpy(prog->info->used_maps, env->used_maps,
+ sizeof(u32) * env->used_map_cnt);
+ prog->info->used_map_cnt = env->used_map_cnt;
+ }
+
+ kfree(env);
+ return ret;
+}
--
1.7.9.5