Re: [PATCH v3 06/13] KVM: x86/xen: Enforce 4-byte alignment of vcpu_info registration

[Paul Durrant <xadimgnik@gmail.com>]

On 31/08/2026 22:26, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> 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 <dwmw@amazon.co.uk>
> ---
>   arch/x86/kvm/xen.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
Reviewed-by: Paul Durrant <paul@xen.org>