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

[Alexei Starovoitov]

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.
How do you want this fix routed? via bpf tree?