From: Peter Zijlstra <peterz@infradead.org>
To: Richard Patel <ripatel@wii.dev>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
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>,
David Laight <david.laight.linux@gmail.com>,
Andy Lutomirski <luto@kernel.org>, Kees Cook <kees@kernel.org>,
Shuah Khan <shuah@kernel.org>,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
Florian Weimer <fweimer@redhat.com>
Subject: Re: [PATCH v2 0/5] Usermode Indirect Branch Tracking
Date: Fri, 5 Jun 2026 21:04:12 +0200 [thread overview]
Message-ID: <20260605190412.GE3117850@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260605184715.3383415-2-ripatel@wii.dev>
On Fri, Jun 05, 2026 at 06:47:11PM +0000, Richard Patel wrote:
> The above sequence does not crash.
>
> With IBT, it should crash at the nop (because an endr64 is expected there).
> The IBT state (WAIT_FOR_ENDBR in IA32_U_CET MSR) is not backed up to the
> signal frame though. So, when userland does a sigreturn, the CPU has
> forgotten that it was doing an indirect branch before the signal.
> (This specifically only occurs with signal handlers that sigreturn.)
>
> This is because IA32_U_CET is part of XSAVE 'supervisor' state, so
> regular XSAVE/XRSTOR can't access it. Doing a manual backup is tricky.
WAIT_FOR_ENDBR should be part of the exception frame with FRED, so if
you're on FRED hardware, this should be fixed IIRC.
next prev parent reply other threads:[~2026-06-05 19:04 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-05 18:47 Richard Patel
2026-06-05 18:47 ` [PATCH v2 1/5] x86: add userspace IBT config option Richard Patel
2026-06-05 18:47 ` [PATCH v2 2/5] x86: shstk: don't clobber IBT bits in U_CET MSR Richard Patel
2026-06-05 18:47 ` [PATCH v2 3/5] x86: expose user IBT via PR_CFI_BRANCH_LANDING_PADS Richard Patel
2026-06-05 18:47 ` [PATCH v2 4/5] x86/entry/vdso: build with IBT support Richard Patel
2026-06-05 19:14 ` Florian Weimer
2026-06-05 18:47 ` [PATCH v2 5/5] selftests/x86: test usermode IBT Richard Patel
2026-06-05 19:04 ` Peter Zijlstra [this message]
2026-06-05 19:34 ` [PATCH v2 0/5] Usermode Indirect Branch Tracking Florian Weimer
2026-06-05 20:32 ` Richard Patel
2026-06-06 13:40 ` Florian Weimer
2026-06-06 23:05 ` Richard Patel
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