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

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Message-ID: <20250515175205.th7pjvord6fum35a@desk>
Date: Thu, 15 May 2025 10:52:05 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Kees Cook <kees@...nel.org>
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 10:41:41AM -0700, Kees Cook wrote:
> 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.

I just tried on the latest upstream, and I am getting the same error. My
earlier bisection was on a stable-rc for 6.14.y:

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?h=linux-6.14.y

... where it was first reported:

https://lore.kernel.org/stable/20250515041659.smhllyarxdwp7cav@desk/