linux-hardening - Re: [REGRESSION] bpf verifier slowdown due to vrealloc() change since 6.15-rc6

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Message-ID: <202505151039.DAA202A@keescook>
Date: Thu, 15 May 2025 10:41:41 -0700
From: Kees Cook <kees@...nel.org>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Shung-Hsi Yu <shung-hsi.yu@...e.com>, bpf@...r.kernel.org,
	linux-mm@...ck.org, Andrii Nakryiko <andrii@...nel.org>,
	Ihor Solodrai <ihor.solodrai@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>,
	Uladzislau Rezki <urezki@...il.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, regressions@...ts.linux.dev,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eduard Zingerman <eddyz87@...il.com>
Subject: Re: [REGRESSION] bpf verifier slowdown due to vrealloc() change
 since 6.15-rc6

On Thu, May 15, 2025 at 10:18:21AM -0700, Pawan Gupta wrote:
> On Thu, May 15, 2025 at 09:51:15AM -0700, Kees Cook wrote:
> > On Thu, May 15, 2025 at 07:51:26AM -0700, Kees Cook wrote:
> > > On May 15, 2025 6:12:25 AM PDT, Shung-Hsi Yu <shung-hsi.yu@...e.com> wrote:
> > > >There is an observable slowdown when running BPF selftests on 6.15-rc6
> > > >kernel[1] built with tools/testing/selftests/bpf/{config,config.x86_64}.
> > > [...]
> > > Where can I find the .config for the slow runs?
> > 
> > Oops, I can read. :) Doing a build now...
> > 
> > > And how do I run the test myself directly?
> > 
> > I found:
> > https://docs.kernel.org/bpf/bpf_devel_QA.html
> > 
> > But it doesn't seem to cover a bunch of stuff (no way to prebuild the
> > tests, no info on building the test modules).
> > 
> > This seems to be needed:
> > 
> > make O=regression-bug -C tools/testing/selftests/bpf/test_kmods
> > 
> > But then the booted kernel doesn't load it (missing signatures?)
> > 
> > Anyway, I'll keep digging...
> 
> After struggling with this for a while, I figured vmtest.sh is the easiest
> way to test bpf:
> 
> ./tools/testing/selftests/bpf/vmtest.sh -i ./test_progs

I can't even build the test_progs. :(

$ make test_progs
...
  CLNG-BPF [test_progs] bpf_iter_tasks.bpf.o
progs/bpf_iter_tasks.c:98:8: error: call to undeclared function 'bpf_copy_from_user_task_str'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   98 |         ret = bpf_copy_from_user_task_str((char *)task_str1, sizeof(task_str1), ptr, task, 0
);
      |               ^
1 error generated.


-- 
Kees Cook