Re: [PATCH v4 bpf-next 1/9] bpf: Move insn_buf[16] to bpf_verifier_env

[Martin KaFai Lau <martin.lau@linux.dev>]

On 8/28/24 6:46 PM, Alexei Starovoitov wrote:
> On Wed, Aug 28, 2024 at 5:41 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>>
>> On Tue, 2024-08-27 at 12:48 -0700, Martin KaFai Lau wrote:
>>> From: Martin KaFai Lau <martin.lau@kernel.org>
>>>
>>> This patch moves the 'struct bpf_insn insn_buf[16]' stack usage
>>> to the bpf_verifier_env. A '#define INSN_BUF_SIZE 16' is also added
>>> to replace the ARRAY_SIZE(insn_buf) usages.
>>>
>>> Both convert_ctx_accesses() and do_misc_fixup() are changed
>>> to use the env->insn_buf.
>>>
>>> It is a prep work for adding the epilogue_buf[16] in a later patch.
>>>
>>> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
>>> ---
>>
>> Not sure if this refactoring is worth it but code looks correct.
>> Note that there is also inline_bpf_loop()
>> (it needs a slightly bigger buffer).
> 
> Probably worth it in the follow up, since people complain that
> this or that function in verifier.c reaches stack size limit
> when compiled with sanitizers.
> These buffers on stack are the biggest consumers.

ok. I will drop this patch for now. Redo it again as a followup and will 
consider inline_bpf_loop() together at that time.

Regarding the stack size, I did notice the compilation warning difference on the 
stack size which I should have put in the commit message.

Before:
./kernel/bpf/verifier.c:22133:5: warning: stack frame size (2584) exceeds limit 
(2048) in 'bpf_check' [-Wframe-larger-than]

After:
./kernel/bpf/verifier.c:22184:5: warning: stack frame size (2264) exceeds limit 
(2048) in 'bpf_check' [-Wframe-larger-than]