[PATCH 1/2] powerpc/bpf: Fix detecting BPF atomic instructions

[Alexei Starovoitov]

On Thu, Jul 1, 2021 at 12:32 PM Naveen N. Rao
<naveen.n.rao at linux.vnet.ibm.com> wrote:
>
> Alexei Starovoitov wrote:
> > On Thu, Jul 1, 2021 at 8:09 AM Naveen N. Rao
> > <naveen.n.rao at linux.vnet.ibm.com> wrote:
> >>
> >> Commit 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other
> >> atomics in .imm") converted BPF_XADD to BPF_ATOMIC and added a way to
> >> distinguish instructions based on the immediate field. Existing JIT
> >> implementations were updated to check for the immediate field and to
> >> reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH)
> >> in the immediate field.
> >>
> >> However, the check added to powerpc64 JIT did not look at the correct
> >> BPF instruction. Due to this, such programs would be accepted and
> >> incorrectly JIT'ed resulting in soft lockups, as seen with the atomic
> >> bounds test. Fix this by looking at the correct immediate value.
> >>
> >> Fixes: 91c960b0056672 ("bpf: Rename BPF_XADD and prepare to encode other atomics in .imm")
> >> Reported-by: Jiri Olsa <jolsa at redhat.com>
> >> Tested-by: Jiri Olsa <jolsa at redhat.com>
> >> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> >> ---
> >> Hi Jiri,
> >> FYI: I made a small change in this patch -- using 'imm' directly, rather
> >> than insn[i].imm. I've still added your Tested-by since this shouldn't
> >> impact the fix in any way.
> >>
> >> - Naveen
> >
> > Excellent debugging! You guys are awesome.
>
> Thanks. Jiri and Brendan did the bulk of the work :)
>
> > How do you want this fix routed? via bpf tree?
>
> Michael has a few BPF patches queued up in powerpc tree for v5.14, so it
> might be easier to take these patches through the powerpc tree unless he
> feels otherwise. Michael?

Works for me. Thanks!