Re: [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2020-05-12 14:35:58
Also in:
bpf, netdev
On 5/8/20 11:53 PM, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@kernel.org> Implement permissions as stated in uapi/linux/capability.h In order to do that the verifier allow_ptr_leaks flag is split into allow_ptr_leaks and bpf_capable flags and they are set as: env->allow_ptr_leaks = perfmon_capable(); env->bpf_capable = bpf_capable(); bpf_capable enables bounded loops, variable stack access and other verifier features. allow_ptr_leaks enable ptr leaks, ptr conversions, subtraction of pointers, etc. It also disables side channel mitigations. That means that the networking BPF program loaded with CAP_BPF + CAP_NET_ADMIN will have speculative checks done by the verifier and other spectre mitigation applied. Such networking BPF program will not be able to leak kernel pointers.
I don't quite follow this part in the code below yet, see my comments.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 6abd5a778fcd..c32a7880fa62 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h@@ -375,6 +375,7 @@ struct bpf_verifier_env { u32 used_map_cnt; /* number of used maps */ u32 id_gen; /* used to generate unique reg IDs */ bool allow_ptr_leaks; + bool bpf_capable; bool seen_direct_write; struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */ const struct bpf_line_info *prev_linfo;diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index 95d77770353c..264a9254dc39 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c@@ -77,7 +77,7 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr) bool percpu = attr->map_type == BPF_MAP_TYPE_PERCPU_ARRAY; int ret, numa_node = bpf_map_attr_numa_node(attr); u32 elem_size, index_mask, max_entries; - bool unpriv = !capable(CAP_SYS_ADMIN); + bool unpriv = !bpf_capable();
So here progs loaded with CAP_BPF will have spectre mitigations bypassed which is the opposite of above statement, no?
u64 cost, array_size, mask64; struct bpf_map_memory mem; struct bpf_array *array;
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diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 6aa11de67315..8f421dd0c4cf 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c@@ -646,7 +646,7 @@ static bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp) void bpf_prog_kallsyms_add(struct bpf_prog *fp) { if (!bpf_prog_kallsyms_candidate(fp) || - !capable(CAP_SYS_ADMIN)) + !bpf_capable()) return; bpf_prog_ksym_set_addr(fp);@@ -824,7 +824,7 @@ static int bpf_jit_charge_modmem(u32 pages) { if (atomic_long_add_return(pages, &bpf_jit_current) > (bpf_jit_limit >> PAGE_SHIFT)) { - if (!capable(CAP_SYS_ADMIN)) { + if (!bpf_capable()) {
Should there still be an upper charge on module mem for !CAP_SYS_ADMIN?
atomic_long_sub(pages, &bpf_jit_current); return -EPERM; }
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 70ad009577f8..a6893746cd87 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c
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@@ -3428,7 +3429,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, * Spectre masking for stack ALU. * See also retrieve_ptr_limit(). */ - if (!env->allow_ptr_leaks) { + if (!env->bpf_capable) {
This needs to stay on env->allow_ptr_leaks, the can_skip_alu_sanitation() does check on env->allow_ptr_leaks as well, otherwise this breaks spectre mitgation when masking alu.
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char tn_buf[48]; tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);@@ -7229,7 +7230,7 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env, insn_stack[env->cfg.cur_stack++] = w; return 1; } else if ((insn_state[w] & 0xF0) == DISCOVERED) { - if (loop_ok && env->allow_ptr_leaks) + if (loop_ok && env->bpf_capable) return 0; verbose_linfo(env, t, "%d: ", t); verbose_linfo(env, w, "%d: ", w);@@ -8338,7 +8339,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx) if (env->max_states_per_insn < states_cnt) env->max_states_per_insn = states_cnt; - if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES) + if (!env->bpf_capable && states_cnt > BPF_COMPLEXITY_LIMIT_STATES) return push_jmp_history(env, cur); if (!add_new_state)@@ -9998,7 +9999,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) insn->code = BPF_JMP | BPF_TAIL_CALL; aux = &env->insn_aux_data[i + delta]; - if (env->allow_ptr_leaks && !expect_blinding && + if (env->bpf_capable && !expect_blinding && prog->jit_requested && !bpf_map_key_poisoned(aux) && !bpf_map_ptr_poisoned(aux) &&@@ -10725,7 +10726,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, env->insn_aux_data[i].orig_idx = i; env->prog = *prog; env->ops = bpf_verifier_ops[env->prog->type]; - is_priv = capable(CAP_SYS_ADMIN); + is_priv = bpf_capable(); if (!btf_vmlinux && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) { mutex_lock(&bpf_verifier_lock);@@ -10766,7 +10767,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, if (attr->prog_flags & BPF_F_ANY_ALIGNMENT) env->strict_alignment = false; - env->allow_ptr_leaks = is_priv; + env->allow_ptr_leaks = perfmon_capable(); + env->bpf_capable = bpf_capable();