From: Ahmed S. Darwish <darwi@linutronix.de>

CPUID leaf 0x2 emits one-byte descriptors in its four output registers
EAX, EBX, ECX, and EDX.  For these descriptors to be valid, the most
significant bit (MSB) of each register must be clear.

Leaf 0x2 parsing at intel.c only validated the MSBs of EAX, EBX, and
ECX, but left EDX unchecked.

Validate EDX's most-significant bit as well.

Fixes: 1aa6feb63bfd ("Port CPU setup code from Linux 2.6")
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250304085152.51092-3-darwi@linutronix.de

Use ARRAY_SIZE() though.

Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 1881148215c6
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
I wasn't really convinced that we strictly need f6bdaab79ee4 ("x86/cpu:
Properly parse CPUID leaf 0x2 TLB descriptor 0x63") as well. Thoughts?

--- a/xen/arch/x86/cpu/intel_cacheinfo.c
+++ b/xen/arch/x86/cpu/intel_cacheinfo.c
@@ -186,7 +186,7 @@ void init_intel_cacheinfo(struct cpuinfo
 			cpuid(2, &regs[0], &regs[1], &regs[2], &regs[3]);
 
 			/* If bit 31 is set, this is an unknown format */
-			for ( j = 0 ; j < 3 ; j++ ) {
+			for ( j = 0; j < ARRAY_SIZE(regs); j++ ) {
 				if ( regs[j] >> 31 )
 					regs[j] = 0;
 			}

On 19/03/2025 11:24 am, Jan Beulich wrote:
> From: Ahmed S. Darwish <darwi@linutronix.de>
>
> CPUID leaf 0x2 emits one-byte descriptors in its four output registers
> EAX, EBX, ECX, and EDX.  For these descriptors to be valid, the most
> significant bit (MSB) of each register must be clear.
>
> Leaf 0x2 parsing at intel.c only validated the MSBs of EAX, EBX, and
> ECX, but left EDX unchecked.
>
> Validate EDX's most-significant bit as well.
>
> Fixes: 1aa6feb63bfd ("Port CPU setup code from Linux 2.6")
> Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Link: https://lore.kernel.org/r/20250304085152.51092-3-darwi@linutronix.de
>
> Use ARRAY_SIZE() though.
>
> Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 1881148215c6
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

> ---
> I wasn't really convinced that we strictly need f6bdaab79ee4 ("x86/cpu:
> Properly parse CPUID leaf 0x2 TLB descriptor 0x63") as well. Thoughts?

I don't think we need it either.