From: Kumar Kartikeya Dwivedi memxor@gmail.com
mainline inclusion from mainline-5.16-rc1 commit a5d8272752416ef1a289e8d843f86b3aa4da0652 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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This patch also modifies the BPF verifier to only return error for invalid kfunc calls specially marked by userspace (with insn->imm == 0, insn->off == 0) after the verifier has eliminated dead instructions. This can be handled in the fixup stage, and skip processing during add and check stages.
If such an invalid call is dropped, the fixup stage will not encounter insn->imm as 0, otherwise it bails out and returns an error.
This will be exposed as weak ksym support in libbpf in later patches.
Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20211002011757.311265-3-memxor@gmail.com (cherry picked from commit a5d8272752416ef1a289e8d843f86b3aa4da0652) Signed-off-by: Wang Yufen wangyufen@huawei.com --- kernel/bpf/verifier.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index c01120be356b..8316eb86268e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1736,6 +1736,15 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset) prog_aux->kfunc_tab = tab; }
+ /* func_id == 0 is always invalid, but instead of returning an error, be + * conservative and wait until the code elimination pass before returning + * error, so that invalid calls that get pruned out can be in BPF programs + * loaded from userspace. It is also required that offset be untouched + * for such calls. + */ + if (!func_id && !offset) + return 0; + if (!btf_tab && offset) { btf_tab = kzalloc(sizeof(*btf_tab), GFP_KERNEL); if (!btf_tab) @@ -6333,6 +6342,10 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn) struct btf *desc_btf; int err;
+ /* skip for now, but return error when we find this in fixup_kfunc_call */ + if (!insn->imm) + return 0; + desc_btf = find_kfunc_desc_btf(env, insn->imm, insn->off, &btf_mod); if (IS_ERR(desc_btf)) return PTR_ERR(desc_btf); @@ -12340,6 +12353,11 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, { const struct bpf_kfunc_desc *desc;
+ if (!insn->imm) { + verbose(env, "invalid kernel function call not eliminated in verifier pass\n"); + return -EINVAL; + } + /* insn->imm has the btf func_id. Replace it with * an address (relative to __bpf_base_call). */