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Re: [PATCH] x86emul/fuzz: sanitize CR4 values
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 24 Aug 2026 10:30:34 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Andrew Mbugua <andrewprecious388@xxxxxxxxx>
- Delivery-date: Mon, 24 Aug 2026 09:30:54 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24/08/2026 8:41 am, Jan Beulich wrote:
> While the CPU policy is obtained from hardware, the CRn values to start
> with are taken from fuzzed input. Since most CR4 bits can only be set when
> the respective feature is indicated as available by CPUID, the emulator
> often only checks the CR4 bit. Without sanitization, assertions like the
> one in emul_test_read_xcr() (checking XSAVE support) could therefore
> trigger.
>
> Omit most paging-only bits from sanitization, as the core emulator doesn't
> itself walk page tables. LA57 wants checking for the bit being used by
> CANONICALIZE_MAYBE().
>
> Reported-by: Andrew Mbugua <andrewprecious388@xxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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