* [PATCH] KVM: Fix wallclock version writing race
@ 2010-05-04 12:02 Avi Kivity
2010-05-04 16:21 ` Avi Kivity
2010-05-04 16:23 ` Glauber Costa
0 siblings, 2 replies; 3+ messages in thread
From: Avi Kivity @ 2010-05-04 12:02 UTC (permalink / raw)
To: Glauber Costa, Marcelo Tosatti; +Cc: kvm
Wallclock writing uses an unprotected global variable to hold the version;
this can cause one guest to interfere with another if both write their
wallclock at the same time.
Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/x86.c | 12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f6f8dad..c3152d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -754,14 +754,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
{
- static int version;
+ int version;
+ int r;
struct pvclock_wall_clock wc;
struct timespec boot;
if (!wall_clock)
return;
- version++;
+ r = kvm_read_guest(kvm, wall_clock, &version, sizeof(version));
+ if (r)
+ return;
+
+ if (version & 1)
+ ++version; /* first time write, random junk */
+
+ ++version;
kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
--
1.7.0.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: Fix wallclock version writing race
2010-05-04 12:02 [PATCH] KVM: Fix wallclock version writing race Avi Kivity
@ 2010-05-04 16:21 ` Avi Kivity
2010-05-04 16:23 ` Glauber Costa
1 sibling, 0 replies; 3+ messages in thread
From: Avi Kivity @ 2010-05-04 16:21 UTC (permalink / raw)
To: Glauber Costa, Marcelo Tosatti; +Cc: kvm, Naphtali Sprei
On 05/04/2010 03:02 PM, Avi Kivity wrote:
> Wallclock writing uses an unprotected global variable to hold the version;
> this can cause one guest to interfere with another if both write their
> wallclock at the same time.
>
> Signed-off-by: Avi Kivity<avi@redhat.com>
>
This was pointed out by Naphtali.
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f6f8dad..c3152d7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -754,14 +754,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>
> static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
> {
> - static int version;
> + int version;
> + int r;
> struct pvclock_wall_clock wc;
> struct timespec boot;
>
> if (!wall_clock)
> return;
>
> - version++;
> + r = kvm_read_guest(kvm, wall_clock,&version, sizeof(version));
> + if (r)
> + return;
> +
> + if (version& 1)
> + ++version; /* first time write, random junk */
> +
> + ++version;
>
> kvm_write_guest(kvm, wall_clock,&version, sizeof(version));
>
>
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: Fix wallclock version writing race
2010-05-04 12:02 [PATCH] KVM: Fix wallclock version writing race Avi Kivity
2010-05-04 16:21 ` Avi Kivity
@ 2010-05-04 16:23 ` Glauber Costa
1 sibling, 0 replies; 3+ messages in thread
From: Glauber Costa @ 2010-05-04 16:23 UTC (permalink / raw)
To: Avi Kivity; +Cc: Marcelo Tosatti, kvm
On Tue, May 04, 2010 at 03:02:24PM +0300, Avi Kivity wrote:
> Wallclock writing uses an unprotected global variable to hold the version;
> this can cause one guest to interfere with another if both write their
> wallclock at the same time.
>
makes sense to me.
ACK.
^ permalink raw reply [flat|nested] 3+ messages in thread
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