[patch 05/15] x86: pvclock: fix flags usage race

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Validity of values returned by pvclock (including flags) is guaranteed by version 
checks.

That is, read of src->flags outside version check protection can refer
to a different paravirt clock update by the hypervisor.

Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>

Index: vsyscall/arch/x86/include/asm/pvclock.h
===================================================================
--- vsyscall.orig/arch/x86/include/asm/pvclock.h
+++ vsyscall/arch/x86/include/asm/pvclock.h
@@ -66,18 +66,21 @@ u64 pvclock_get_nsec_offset(const struct
 
 static __always_inline
 unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
-			       cycle_t *cycles)
+			       cycle_t *cycles, u8 *flags)
 {
 	unsigned version;
 	cycle_t ret, offset;
+	u8 ret_flags;
 
 	version = src->version;
 	rdtsc_barrier();
 	offset = pvclock_get_nsec_offset(src);
 	ret = src->system_time + offset;
+	ret_flags = src->flags;
 	rdtsc_barrier();
 
 	*cycles = ret;
+	*flags = ret_flags;
 	return version;
 }
 
Index: vsyscall/arch/x86/kernel/pvclock.c
===================================================================
--- vsyscall.orig/arch/x86/kernel/pvclock.c
+++ vsyscall/arch/x86/kernel/pvclock.c
@@ -50,13 +50,14 @@ cycle_t pvclock_clocksource_read(struct 
 	unsigned version;
 	cycle_t ret;
 	u64 last;
+	u8 flags;
 
 	do {
-		version = __pvclock_read_cycles(src, &ret);
+		version = __pvclock_read_cycles(src, &ret, &flags);
 	} while ((src->version & 1) || version != src->version);
 
 	if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
-		(src->flags & PVCLOCK_TSC_STABLE_BIT))
+		(flags & PVCLOCK_TSC_STABLE_BIT))
 		return ret;
 
 	/*


--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux