[Devel] [PATCH vz8 1/2] x86, cpuinfo: Fix race on parallel /proc/cpuinfo read

[Andrey Ryabinin]

If several threads read /proc/cpuinfo some can see in 'flags'
values from c->x86_capability, before __do_cpuid_fault() called
and masks applied. Fix this by forming 'flags' on stack first
and copy them in per_cpu(cpu_flags, cpu) as a last step.

https://jira.sw.ru/browse/PSBM-121823
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 arch/x86/kernel/cpu/proc.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 4fe1577d5e6f..4cc2951e34fb 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -69,11 +69,11 @@ static DEFINE_PER_CPU(struct cpu_flags, cpu_flags);
 static void init_cpu_flags(void *dummy)
 {
 	int cpu = smp_processor_id();
-	struct cpu_flags *flags = &per_cpu(cpu_flags, cpu);
+	struct cpu_flags flags;
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 	unsigned int eax, ebx, ecx, edx;
 
-	memcpy(flags->val, c->x86_capability, NCAPINTS * sizeof(u32));
+	memcpy(&flags, c->x86_capability, sizeof(flags));
 
 	/*
 	 * Clear feature bits masked using cpuid masking/faulting.
@@ -81,26 +81,27 @@ static void init_cpu_flags(void *dummy)
 
 	if (c->cpuid_level >= 0x00000001) {
 		__do_cpuid_fault(0x00000001, 0, &eax, &ebx, &ecx, &edx);
-		flags->val[4] &= ecx;
-		flags->val[0] &= edx;
+		flags.val[4] &= ecx;
+		flags.val[0] &= edx;
 	}
 
 	if (c->cpuid_level >= 0x00000007) {
 		__do_cpuid_fault(0x00000007, 0, &eax, &ebx, &ecx, &edx);
-		flags->val[9] &= ebx;
+		flags.val[9] &= ebx;
 	}
 
 	if ((c->extended_cpuid_level & 0xffff0000) == 0x80000000 &&
 	    c->extended_cpuid_level >= 0x80000001) {
 		__do_cpuid_fault(0x80000001, 0, &eax, &ebx, &ecx, &edx);
-		flags->val[6] &= ecx;
-		flags->val[1] &= edx;
+		flags.val[6] &= ecx;
+		flags.val[1] &= edx;
 	}
 
 	if (c->cpuid_level >= 0x0000000d) {
 		__do_cpuid_fault(0x0000000d, 1, &eax, &ebx, &ecx, &edx);
-		flags->val[10] &= eax;
+		flags.val[10] &= eax;
 	}
+	memcpy(&per_cpu(cpu_flags, cpu), &flags, sizeof(flags));
 }
 
 static int show_cpuinfo(struct seq_file *m, void *v)
-- 
2.26.2