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Wed, 02 Sep 2026 05:29:23 -0700 (PDT) From: Paul Durrant X-Google-Original-From: Paul Durrant Message-ID: Date: Wed, 2 Sep 2026 13:29:22 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/13] KVM: x86/xen: Enforce 4-byte alignment of vcpu_info registration To: David Woodhouse , seanjc@google.com, pbonzini@redhat.com Cc: joao.m.martins@oracle.com, boris.ostrovsky@oracle.com, ankur.a.arora@oracle.com, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, x86@kernel.org, syzbot+208f7f3e5f59c11aeb90@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, suryasaimadhu369@gmail.com, lkp@intel.com, nicoyip.dev@gmail.com, frn1furkan10@gmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, imv4bel@gmail.com References: <20260831213632.81023-1-dwmw2@infradead.org> <20260831213632.81023-7-dwmw2@infradead.org> Content-Language: en-US In-Reply-To: <20260831213632.81023-7-dwmw2@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 31/08/2026 22:26, David Woodhouse wrote: > From: David Woodhouse > > Xen's map_guest_area() enforces that vcpu_info is aligned to > sizeof(xen_ulong_t). KVM has no such check, allowing a guest to > register vcpu_info at an arbitrary byte alignment. > > Enforce unconditional 4-byte alignment regardless of the current > shinfo mode. This is sufficient because subsequent commits ensure > that all locked atomic operations on vcpu_info fields use at most > 32-bit accesses. Return -ENXIO on failure, matching Xen's > map_guest_area() behaviour for unaligned requests. > > Originally observed in review of an unrelated patch: > https://lore.kernel.org/all/20260604193554.1BA311F00893@smtp.kernel.org/ > > Cc: stable@vger.kernel.org > Fixes: 73e69a86347a ("KVM: x86/xen: register vcpu info") > Reported-by: sashiko-bot@kernel.org > Closes: https://lore.kernel.org/all/20260604193554.1BA311F00893@smtp.kernel.org > Assisted-by: Kiro:claude-opus-4.6-1m > Signed-off-by: David Woodhouse > --- > arch/x86/kvm/xen.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > Reviewed-by: Paul Durrant