Messages in this thread | | | From | Ravi Bangoria <> | Subject | Re: [PATCH] x86 bpf: Fix extable offset calculation | Date | Fri, 25 Jun 2021 11:52:24 +0530 |
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On 6/25/21 9:31 AM, Alexei Starovoitov wrote: > On Tue, Jun 22, 2021 at 4:01 AM Ravi Bangoria > <ravi.bangoria@linux.ibm.com> wrote: >> >> 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 <ravi.bangoria@linux.ibm.com> >> --- >> 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.
Thanks.
> Could you send a followup patch with a selftest, so I don't make > the same mistake again ? ;)
Unfortunately extable gets involved only for bad kernel pointers and ideally there should not be any bad pointer in kernel. So there is no easy way to create a proper selftest for this.
Ravi
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