x86/cacheinfo: Validate CPUID leaf 0x2 EDX output

["Ahmed S. Darwish" <darwi@xxxxxxxxxxxxx>]

From: Ahmed S. Darwish <darwi@xxxxxxxxxxxxx>

commit 8177c6bedb7013cf736137da586cf783922309dd upstream.

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.

The historical Git commit:

  019361a20f016 ("- pre6: Intel: start to add Pentium IV specific stuff (128-byte cacheline etc)...")

introduced leaf 0x2 output parsing.  It only validated the MSBs of EAX,
EBX, and ECX, but left EDX unchecked.

Validate EDX's most-significant bit.

Signed-off-by: Ahmed S. Darwish <darwi@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250304085152.51092-2-darwi@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/cacheinfo.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -795,7 +795,7 @@ 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 < 4 ; j++)
 				if (regs[j] & (1 << 31))
 					regs[j] = 0;
 


Patches currently in stable-queue which might be from darwi@xxxxxxxxxxxxx are

queue-5.4/x86-cacheinfo-validate-cpuid-leaf-0x2-edx-output.patch
queue-5.4/x86-cpu-properly-parse-cpuid-leaf-0x2-tlb-descriptor-0x63.patch
queue-5.4/x86-cpu-validate-cpuid-leaf-0x2-edx-output.patch