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>,
Alexander Mikhalitsyn <alexander@mihalicyn.com>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 6/8] x86/fpu: Fix potential underflow in xstate_calculate_size()
Date: Wed, 2 Sep 2026 14:15:45 -0700 [thread overview]
Message-ID: <8fcc533a-ab78-4221-82d9-b09cbc13f221@intel.com> (raw)
In-Reply-To: <20260817042048.1579415-7-avagin@google.com>
On 8/16/2026 9:20 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.
I think this fix makes sense before applying it to something that
user-space provides via the sigframe:
Reviewed-by: Chang S. Bae <chang.seok.bae@intel.com>
Thanks,
Chang
next prev parent reply other threads:[~2026-09-02 21:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-17 4:20 [PATCH v4 0/8] x86/fpu: Restore and reinforce signal frame portability Andrei Vagin
2026-08-17 4:20 ` [PATCH 1/8] x86/fpu: Document " Andrei Vagin
2026-09-02 21:15 ` Chang S. Bae
2026-09-03 4:51 ` Borislav Petkov
2026-08-17 4:20 ` [PATCH 2/8] x86/fpu: Clean up and rename variables in signal frame handling Andrei Vagin
2026-08-17 4:20 ` [PATCH 3/8] x86/fpu: Split __fpu_restore_sig to extract compat path Andrei Vagin
2026-09-02 21:15 ` Chang S. Bae
2026-08-17 4:20 ` [PATCH 4/8] x86/fpu: Document reasoning of FX-only fallback Andrei Vagin
2026-09-02 21:15 ` Chang S. Bae
2026-08-17 4:20 ` [PATCH 5/8] selftests/x86: Add a test for signal frame FPU portability Andrei Vagin
2026-08-17 4:20 ` [PATCH 6/8] x86/fpu: Fix potential underflow in xstate_calculate_size() Andrei Vagin
2026-09-02 21:15 ` Chang S. Bae [this message]
2026-08-17 4:20 ` [PATCH 7/8] x86/fpu: Pre-fault only required size of xstate buffer Andrei Vagin
2026-09-02 21:15 ` Chang S. Bae
2026-08-17 4:20 ` [PATCH 8/8] selftests/x86: Add a sigframe insufficient xstate_size test Andrei Vagin
2026-09-02 21:16 ` Chang S. Bae
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