[PATCH 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM
From: Kees Cook <hidden>
Date: 2021-09-27 18:27:13
Also in:
bpf, linux-hardening, lkml
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
In order to keep ahead of cases in the kernel where Control Flow Integrity (CFI) may trip over function call casts, enabling -Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes various warnings and is one of the last places in the kernel triggering this warning. Most places using BPF_CAST_CALL actually just want a void * to perform math on. It's not actually performing a call, so just use a different helper to get the void *, by way of the new BPF_CALL_IMM() helper, which can clean up a common copy/paste idiom as well. This change results in no object code difference. Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Martin KaFai Lau <redacted> Cc: Song Liu <redacted> Cc: Yonghong Song <redacted> Cc: John Fastabend <john.fastabend@gmail.com> Cc: KP Singh <kpsingh@kernel.org> Cc: netdev@vger.kernel.org Cc: bpf@vger.kernel.org Cc: Gustavo A. R. Silva <gustavoars@kernel.org> Link: https://github.com/KSPP/linux/issues/20 Signed-off-by: Kees Cook <redacted> --- include/linux/filter.h | 6 +++++- kernel/bpf/hashtab.c | 6 +++--- kernel/bpf/verifier.c | 26 +++++++++----------------- 3 files changed, 17 insertions(+), 21 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 4a93c12543ee..6c247663d4ce 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h@@ -365,13 +365,17 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) #define BPF_CAST_CALL(x) \ ((u64 (*)(u64, u64, u64, u64, u64))(x)) +/* Convert function address to BPF immediate */ + +#define BPF_CALL_IMM(x) ((void *)(x) - (void *)__bpf_call_base) + #define BPF_EMIT_CALL(FUNC) \ ((struct bpf_insn) { \ .code = BPF_JMP | BPF_CALL, \ .dst_reg = 0, \ .src_reg = 0, \ .off = 0, \ - .imm = ((FUNC) - __bpf_call_base) }) + .imm = BPF_CALL_IMM(FUNC) }) /* Raw code statement block */
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 32471ba02708..3d8f9d6997d5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c@@ -668,7 +668,7 @@ static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem, (void *(*)(struct bpf_map *map, void *key))NULL)); - *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem)); + *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem); *insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1); *insn++ = BPF_ALU64_IMM(BPF_ADD, ret, offsetof(struct htab_elem, key) +
@@ -709,7 +709,7 @@ static int htab_lru_map_gen_lookup(struct bpf_map *map, BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem, (void *(*)(struct bpf_map *map, void *key))NULL)); - *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem)); + *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem); *insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4); *insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret, offsetof(struct htab_elem, lru_node) +
@@ -2397,7 +2397,7 @@ static int htab_of_map_gen_lookup(struct bpf_map *map, BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem, (void *(*)(struct bpf_map *map, void *key))NULL)); - *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem)); + *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem); *insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2); *insn++ = BPF_ALU64_IMM(BPF_ADD, ret, offsetof(struct htab_elem, key) +
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e76b55917905..15068fa7b16d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c@@ -1730,7 +1730,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id) desc = &tab->descs[tab->nr_descs++]; desc->func_id = func_id; - desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base; + desc->imm = BPF_CALL_IMM(addr); err = btf_distill_func_proto(&env->log, btf_vmlinux, func_proto, func_name, &desc->func_model);
@@ -12469,8 +12469,7 @@ static int jit_subprogs(struct bpf_verifier_env *env) if (!bpf_pseudo_call(insn)) continue; subprog = insn->off; - insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(func[subprog]->bpf_func); } /* we use the aux data to keep a list of the start addresses
@@ -12950,32 +12949,25 @@ static int do_misc_fixups(struct bpf_verifier_env *env) patch_map_ops_generic: switch (insn->imm) { case BPF_FUNC_map_lookup_elem: - insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_lookup_elem); continue; case BPF_FUNC_map_update_elem: - insn->imm = BPF_CAST_CALL(ops->map_update_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_update_elem); continue; case BPF_FUNC_map_delete_elem: - insn->imm = BPF_CAST_CALL(ops->map_delete_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_delete_elem); continue; case BPF_FUNC_map_push_elem: - insn->imm = BPF_CAST_CALL(ops->map_push_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_push_elem); continue; case BPF_FUNC_map_pop_elem: - insn->imm = BPF_CAST_CALL(ops->map_pop_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_pop_elem); continue; case BPF_FUNC_map_peek_elem: - insn->imm = BPF_CAST_CALL(ops->map_peek_elem) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_peek_elem); continue; case BPF_FUNC_redirect_map: - insn->imm = BPF_CAST_CALL(ops->map_redirect) - - __bpf_call_base; + insn->imm = BPF_CALL_IMM(ops->map_redirect); continue; }
--
2.30.2