| Message ID | 20210622110026.1157847-1-ravi.bangoria@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | x86 bpf: Fix extable offset calculation | expand |
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. Could you send a followup patch with a selftest, so I don't make the same mistake again ? ;)
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
On Thu, Jun 24, 2021 at 11:22 PM Ravi Bangoria <ravi.bangoria@linux.ibm.com> wrote: > > 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. Right. We have lib/test_bpf.c kernel module for such cases.
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); s64 delta; /* populate jmp_offset for JMP above */
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(-)