5.4-stable review patch. If anyone has any objections, please let me know.
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From: Ahmed S. Darwish darwi@linutronix.de
[ Upstream commit cc663ba3fe383a628a812f893cc98aafff39ab04 ]
CPUID(0x80000000).EAX returns the max extended CPUID leaf available. On x86-32 machines without an extended CPUID range, a CPUID(0x80000000) query will just repeat the output of the last valid standard CPUID leaf on the CPU; i.e., a garbage values. Current tip:x86/cpu code protects against this by doing:
eax = cpuid_eax(0x80000000); c->extended_cpuid_level = eax;
if ((eax & 0xffff0000) == 0x80000000) { // CPU has an extended CPUID range. Check for 0x80000001 if (eax >= 0x80000001) { cpuid(0x80000001, ...); } }
This is correct so far. Afterwards though, the same possibly broken EAX value is used to check the availability of other extended CPUID leaves:
if (c->extended_cpuid_level >= 0x80000007) ... if (c->extended_cpuid_level >= 0x80000008) ... if (c->extended_cpuid_level >= 0x8000000a) ... if (c->extended_cpuid_level >= 0x8000001f) ...
which is invalid. Fix this by immediately setting the CPU's max extended CPUID leaf to zero if CPUID(0x80000000).EAX doesn't indicate a valid CPUID extended range.
While at it, add a comment, similar to kernel/head_32.S, clarifying the CPUID(0x80000000) sanity check.
References: 8a50e5135af0 ("x86-32: Use symbolic constants, safer CPUID when enabling EFER.NX") Fixes: 3da99c977637 ("x86: make (early)_identify_cpu more the same between 32bit and 64 bit") Signed-off-by: Ahmed S. Darwish darwi@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Andrew Cooper andrew.cooper3@citrix.com Cc: H. Peter Anvin hpa@zytor.com Cc: John Ogness john.ogness@linutronix.de Cc: x86-cpuid@lists.linux.dev Link: https://lore.kernel.org/r/20250506050437.10264-3-darwi@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/common.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index ae9d8aa3ae48e..bd29a436e87e8 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -934,17 +934,18 @@ void get_cpu_cap(struct cpuinfo_x86 *c) c->x86_capability[CPUID_D_1_EAX] = eax; }
- /* AMD-defined flags: level 0x80000001 */ + /* + * Check if extended CPUID leaves are implemented: Max extended + * CPUID leaf must be in the 0x80000001-0x8000ffff range. + */ eax = cpuid_eax(0x80000000); - c->extended_cpuid_level = eax; + c->extended_cpuid_level = ((eax & 0xffff0000) == 0x80000000) ? eax : 0;
- if ((eax & 0xffff0000) == 0x80000000) { - if (eax >= 0x80000001) { - cpuid(0x80000001, &eax, &ebx, &ecx, &edx); + if (c->extended_cpuid_level >= 0x80000001) { + cpuid(0x80000001, &eax, &ebx, &ecx, &edx);
- c->x86_capability[CPUID_8000_0001_ECX] = ecx; - c->x86_capability[CPUID_8000_0001_EDX] = edx; - } + c->x86_capability[CPUID_8000_0001_ECX] = ecx; + c->x86_capability[CPUID_8000_0001_EDX] = edx; }
if (c->extended_cpuid_level >= 0x80000007) {