From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Andrei Vagin <avagin@google.com>,
Thomas Gleixner <tglx@kernel.org>,
"Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Cc: <linux-kernel@vger.kernel.org>, <criu@lists.linux.dev>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 05/10] x86/fpu: Fix potential underflow in xstate_calculate_size()
Date: Tue, 30 Jun 2026 12:23:51 -0700 [thread overview]
Message-ID: <4b76762c-387e-4f26-8e0f-155802b13bce@intel.com> (raw)
In-Reply-To: <20260615193716.1843340-6-avagin@google.com>
On 6/15/2026 12:37 PM, Andrei Vagin wrote:
> xstate_calculate_size() calculates the size required for a given set of
> xfeatures. It determines the topmost feature by finding the most
> significant bit in xfeatures using fls64(xfeatures) - 1.
>
> If xfeatures is 0, fls64(0) returns 0, and topmost becomes -1.
> Previously, topmost was unsigned int, so -1 underflowed to UINT_MAX.
> This caused the subsequent check `topmost <= XFEATURE_SSE` to fail, and
> the code proceeded to access xstate arrays using topmost (UINT_MAX) as
> an index, leading to an out-of-bounds access.
>
> Fix this by checking if xfeatures only contains legacy features (FP/SSE)
> or is empty (xfeatures <= XFEATURE_MASK_FPSSE) before calculating
> topmost.
Just a nit: this appears to prepare for the changes in patch7. If so, it
may make sense to move it just before that?
next prev parent reply other threads:[~2026-06-30 19:23 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-15 19:37 [PATCH v3 0/10] x86/fpu: Restore and reinforce signal frame portability Andrei Vagin
2026-06-15 19:37 ` [PATCH 01/10] x86/fpu: Document " Andrei Vagin
2026-06-26 13:51 ` Alexander Mikhalitsyn
2026-06-30 19:23 ` Chang S. Bae
2026-06-15 19:37 ` [PATCH 02/10] x86/fpu: Clean up and rename variables in signal frame handling Andrei Vagin
2026-06-26 17:05 ` Alexander Mikhalitsyn
2026-06-15 19:37 ` [PATCH 03/10] x86/fpu: Split __fpu_restore_sig to extract compat path Andrei Vagin
2026-06-26 17:20 ` Alexander Mikhalitsyn
2026-06-15 19:37 ` [PATCH 04/10] x86/fpu: Document reasoning of FX-only fallback Andrei Vagin
2026-06-26 14:22 ` Alexander Mikhalitsyn
2026-06-30 19:23 ` Chang S. Bae
2026-06-15 19:37 ` [PATCH 05/10] x86/fpu: Fix potential underflow in xstate_calculate_size() Andrei Vagin
2026-06-26 14:32 ` Alexander Mikhalitsyn
2026-06-30 19:23 ` Chang S. Bae [this message]
2026-06-15 19:37 ` [PATCH 06/10] selftests/x86: Add a test for signal frame FPU portability Andrei Vagin
2026-06-26 14:39 ` Alexander Mikhalitsyn
2026-06-15 19:37 ` [PATCH 07/10] x86/fpu: Pre-fault only required size of xstate buffer Andrei Vagin
2026-06-26 17:28 ` Alexander Mikhalitsyn
2026-06-15 19:37 ` [PATCH 08/10] selftests/x86: Add a sigframe insufficient xstate_size test Andrei Vagin
2026-06-26 15:02 ` Alexander Mikhalitsyn
2026-06-15 19:37 ` [PATCH 09/10] x86/fpu: Allow restoring signal frames with larger xstate_size Andrei Vagin
2026-06-26 17:32 ` Alexander Mikhalitsyn
2026-06-30 19:23 ` Chang S. Bae
2026-07-01 0:48 ` Andrei Vagin
2026-07-06 17:08 ` Chang S. Bae
2026-07-07 20:27 ` Andrei Vagin
2026-07-09 21:14 ` Chang S. Bae
2026-07-10 22:24 ` Chang S. Bae
2026-06-15 19:37 ` [PATCH 10/10] selftests/x86: Check restoring FPU state " Andrei Vagin
2026-06-26 15:12 ` Alexander Mikhalitsyn
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