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.

Cc: stable@vger.kernel.org
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
---
 arch/x86/kernel/cpu/cacheinfo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index e6fa03ed9172..a6c6bccfa8b8 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -808,7 +808,7 @@ void init_intel_cacheinfo(struct cpuinfo_x86 *c)
 			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;
 
-- 
2.48.1

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     8177c6bedb7013cf736137da586cf783922309dd
Gitweb:        https://git.kernel.org/tip/8177c6bedb7013cf736137da586cf783922309dd
Author:        Ahmed S. Darwish <darwi@linutronix.de>
AuthorDate:    Tue, 04 Mar 2025 09:51:12 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 09:59:14 +01:00

x86/cacheinfo: Validate CPUID leaf 0x2 EDX output

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@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250304085152.51092-2-darwi@linutronix.de
---
 arch/x86/kernel/cpu/cacheinfo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index e6fa03e..a6c6bcc 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -808,7 +808,7 @@ void init_intel_cacheinfo(struct cpuinfo_x86 *c)
 			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;