Re: [PATCH] x86 bpf: Fix extable offset calculation
From: Alexei Starovoitov <hidden>
Date: 2021-06-25 04:01:24
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lkml, netdev
On Tue, Jun 22, 2021 at 4:01 AM Ravi Bangoria [off-list ref] wrote:
quoted hunk ↗ jump to hunk
commit 4c5de127598e1 ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.") is emitting couple of instructions before actual load. Consider those additional instructions while calculating extable offset. Fixes: 4c5de127598e1 ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.") Signed-off-by: Ravi Bangoria <redacted> --- arch/x86/net/bpf_jit_comp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 2a2e290fa5d8..231a8178cc11 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c@@ -1297,7 +1297,7 @@ st: if (is_imm8(insn->off)) emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off); if (BPF_MODE(insn->code) == BPF_PROBE_MEM) { struct exception_table_entry *ex; - u8 *_insn = image + proglen; + u8 *_insn = image + proglen + (u8)(start_of_ldx - temp);
Great debugging and the fix. Thanks a lot. I've dropped (u8) cast, kept (), and applied to bpf tree. I think it looks cleaner without that cast. Could you send a followup patch with a selftest, so I don't make the same mistake again ? ;)