linux-kernel - Re: [PATCH 5/5] selftests/bpf: make cfi

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQKXUUNn=P=2-UECF1X7SR+oqm4xsr-2trpgTy1q+0c5FQ@mail.gmail.com>
Date: Wed, 31 Dec 2025 10:13:47 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Caleb Sander Mateos <csander@...estorage.com>
Cc: bot+bpf-ci@...nel.org, Jiri Kosina <jikos@...nel.org>, 
	Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>, 
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Benjamin Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>, 
	Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, 
	Jiri Pirko <jiri@...nulli.us>, "D. Wythe" <alibuda@...ux.alibaba.com>, 
	Dust Li <dust.li@...ux.alibaba.com>, sidraya@...ux.ibm.com, wenjia@...ux.ibm.com, 
	mjambigi@...ux.ibm.com, Tony Lu <tonylu@...ux.alibaba.com>, guwen@...ux.alibaba.com, 
	Shuah Khan <shuah@...nel.org>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	"open list:HID CORE LAYER" <linux-input@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, sched-ext@...ts.linux.dev, 
	linux-rdma@...r.kernel.org, linux-s390 <linux-s390@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Chris Mason <clm@...a.com>, 
	Ihor Solodrai <ihor.solodrai@...ux.dev>
Subject: Re: [PATCH 5/5] selftests/bpf: make cfi_stubs globals const

On Wed, Dec 31, 2025 at 10:09 AM Caleb Sander Mateos
<csander@...estorage.com> wrote:
>
> On Wed, Dec 31, 2025 at 10:04 AM <bot+bpf-ci@...nel.org> wrote:
> >
> > > diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > > index 90c4b1a51de6..5e460b1dbdb6 100644
> > > --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > > +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> >
> > [ ... ]
> >
> > > @@ -1275,7 +1275,7 @@ bpf_testmod_ops__test_return_ref_kptr(int dummy, struct task_struct *task__ref,
> > >       return NULL;
> > >  }
> > >
> > > -static struct bpf_testmod_ops __bpf_testmod_ops = {
> > > +static const struct bpf_testmod_ops __bpf_testmod_ops = {
> > >       .test_1 = bpf_testmod_test_1,
> > >       .test_2 = bpf_testmod_test_2,
> >
> > Is it safe to make __bpf_testmod_ops const here? In bpf_testmod_init(),
> > this struct is modified at runtime:
> >
> >     tramp = (void **)&__bpf_testmod_ops.tramp_1;
> >     while (tramp <= (void **)&__bpf_testmod_ops.tramp_40)
> >         *tramp++ = bpf_testmod_tramp;
> >
> > Writing to a const-qualified object is undefined behavior and may cause a
> > protection fault when the compiler places this in read-only memory. Would
> > the module fail to load on systems where .rodata is actually read-only?
>
> Yup, that's indeed the bug caught by KASAN. Missed this mutation at
> init time, I'll leave __bpf_testmod_ops as mutable.

No. You're missing the point. The whole patch set is no go.
The pointer to cfi stub can be updated just as well.