On 6/25/21 9:31 AM, Alexei Starovoitov wrote:
On Tue, Jun 22, 2021 at 4:01 AM Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> --- 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
