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

[Naveen N. Rao]

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?

This also needs to be tagged for stable:
Cc: stable at vger.kernel.org # 5.12+


- Naveen