| Message ID | 20230104014709.9375-1-sunhao.th@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d3178e8a434b58678d99257c0387810a24042fb6 |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: skip invalid kfunc call in backtrack_insn | expand |
On 1/3/23 5:47 PM, Hao Sun wrote: > The verifier skips invalid kfunc call in check_kfunc_call(), which > would be captured in fixup_kfunc_call() if such insn is not > eliminated by dead code elimination. However, this can lead to the > following warning in backtrack_insn(), alse see [1]: > > ------------[ cut here ]------------ > verifier backtracking bug > WARNING: CPU: 6 PID: 8646 at kernel/bpf/verifier.c:2756 backtrack_insn > kernel/bpf/verifier.c:2756 > __mark_chain_precision kernel/bpf/verifier.c:3065 > mark_chain_precision kernel/bpf/verifier.c:3165 > adjust_reg_min_max_vals kernel/bpf/verifier.c:10715 > check_alu_op kernel/bpf/verifier.c:10928 > do_check kernel/bpf/verifier.c:13821 [inline] > do_check_common kernel/bpf/verifier.c:16289 > ... > > So make backtracking conservative with this by returning ENOTSUPP. > > [1] https://lore.kernel.org/bpf/CACkBjsaXNceR8ZjkLG=dT3P=4A8SBsg0Z5h5PWLryF5=ghKq=g@mail.gmail.com/ > > Signed-off-by: Hao Sun <sunhao.th@gmail.com> Acked-by: Yonghong Song <yhs@fb.com>
Hello: This patch was applied to bpf/bpf.git (master) by Daniel Borkmann <daniel@iogearbox.net>: On Wed, 4 Jan 2023 09:47:09 +0800 you wrote: > The verifier skips invalid kfunc call in check_kfunc_call(), which > would be captured in fixup_kfunc_call() if such insn is not > eliminated by dead code elimination. However, this can lead to the > following warning in backtrack_insn(), alse see [1]: > > ------------[ cut here ]------------ > verifier backtracking bug > WARNING: CPU: 6 PID: 8646 at kernel/bpf/verifier.c:2756 backtrack_insn > kernel/bpf/verifier.c:2756 > __mark_chain_precision kernel/bpf/verifier.c:3065 > mark_chain_precision kernel/bpf/verifier.c:3165 > adjust_reg_min_max_vals kernel/bpf/verifier.c:10715 > check_alu_op kernel/bpf/verifier.c:10928 > do_check kernel/bpf/verifier.c:13821 [inline] > do_check_common kernel/bpf/verifier.c:16289 > ... > > [...] Here is the summary with links: - bpf: skip invalid kfunc call in backtrack_insn https://git.kernel.org/bpf/bpf/c/d3178e8a434b You are awesome, thank you!
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4a25375ebb0d..04887b1e4178 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2750,6 +2750,12 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, */ if (insn->src_reg == 0 && is_callback_calling_function(insn->imm)) return -ENOTSUPP; + /* kfunc with imm==0 is invalid and fixup_kfunc_call will + * catch this error later. Make backtracking conservative + * with ENOTSUPP. + */ + if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL && insn->imm == 0) + return -ENOTSUPP; /* regular helper call sets R0 */ *reg_mask &= ~1; if (*reg_mask & 0x3f) {
The verifier skips invalid kfunc call in check_kfunc_call(), which would be captured in fixup_kfunc_call() if such insn is not eliminated by dead code elimination. However, this can lead to the following warning in backtrack_insn(), alse see [1]: ------------[ cut here ]------------ verifier backtracking bug WARNING: CPU: 6 PID: 8646 at kernel/bpf/verifier.c:2756 backtrack_insn kernel/bpf/verifier.c:2756 __mark_chain_precision kernel/bpf/verifier.c:3065 mark_chain_precision kernel/bpf/verifier.c:3165 adjust_reg_min_max_vals kernel/bpf/verifier.c:10715 check_alu_op kernel/bpf/verifier.c:10928 do_check kernel/bpf/verifier.c:13821 [inline] do_check_common kernel/bpf/verifier.c:16289 ... So make backtracking conservative with this by returning ENOTSUPP. [1] https://lore.kernel.org/bpf/CACkBjsaXNceR8ZjkLG=dT3P=4A8SBsg0Z5h5PWLryF5=ghKq=g@mail.gmail.com/ Signed-off-by: Hao Sun <sunhao.th@gmail.com> --- kernel/bpf/verifier.c | 6 ++++++ 1 file changed, 6 insertions(+) base-commit: acd3b7768048fe338248cdf43ccfbf8c084a6bc1