From: Richard Patel <ripatel@wii.dev>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org, Rick Edgecombe <rick.p.edgecombe@intel.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Kees Cook <kees@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Shuah Khan <shuah@kernel.org>,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/7] x86: ban 32-bit sigreturn when user IBT enabled
Date: Tue, 19 May 2026 00:14:34 +0000 [thread overview]
Message-ID: <aguralnvvMKzIDxH@wii.dev> (raw)
In-Reply-To: <F10D66BF-C851-4B14-81D7-E5F1E15A325B@zytor.com>
On Mon, May 18, 2026 at 01:22:19PM -0700, H. Peter Anvin wrote:
> On May 17, 2026 11:30:21 AM PDT, Richard Patel <ripatel@wii.dev> wrote:
> >IBT is not implemented for 32-bit and cannot be enabled using a
> >32-bit syscall. However, a 64-bit thread could far jump into 32-bit.
> >Therefore, 32-bit sigreturn must be banned until IBT supports that
> >environment.
> Dumb question: is there any reason not to just enable it for 32 bits? It doesn't seem that it would be that big of a delta to Just Do It.™
>
> That being said, I suspect the number of users will be very small if any.
Yes, partially, good call. It'd be tricky for legacy IA32 signals.
sigframe_ia32 would need to be modified I think. For rt_sigframe_ia32
(rt_sigreturn) we can put it in ucontext_ia32::uc_flags.
I'll fix it in v2 later this week and add tests.
next prev parent reply other threads:[~2026-05-19 0:20 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-17 18:30 [PATCH 0/7] Usermode Indirect Branch Tracking Richard Patel
2026-05-17 18:30 ` [PATCH 1/7] x86: add userspace IBT config option Richard Patel
2026-05-17 18:30 ` [PATCH 2/7] x86: shstk: don't clobber IBT bits in U_CET MSR Richard Patel
2026-05-17 18:30 ` [PATCH 3/7] x86: signal handler support for IBT Richard Patel
2026-05-17 18:30 ` [PATCH 4/7] x86: ban 32-bit sigreturn when user IBT enabled Richard Patel
2026-05-18 20:22 ` H. Peter Anvin
2026-05-19 0:14 ` Richard Patel [this message]
2026-05-17 18:30 ` [PATCH 5/7] x86: expose user IBT via PR_CFI_BRANCH_LANDING_PADS Richard Patel
2026-05-18 6:46 ` Richard Patel
2026-05-17 18:30 ` [PATCH 6/7] x86/entry/vdso: build with IBT support Richard Patel
2026-05-17 18:30 ` [PATCH 7/7] selftests/x86: test usermode IBT Richard Patel
2026-05-18 7:36 ` [PATCH 0/7] Usermode Indirect Branch Tracking Peter Zijlstra
2026-05-18 16:25 ` Richard Patel
2026-05-18 19:31 ` Peter Zijlstra
2026-05-19 9:33 ` David Laight
2026-05-19 9:40 ` Peter Zijlstra
2026-05-19 13:14 ` Richard Patel
2026-05-19 13:28 ` David Laight
2026-05-19 14:18 ` Richard Patel
2026-05-19 14:42 ` Peter Zijlstra
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