2007-06-15 09:43:47

by Avi Kivity

Subject: [GIT PULL] KVM fix for 2.6.22

Linus,

Please pull from the repository and branch at

git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm.git for-linus

to get a fix for a fairly critical bug which allows, under certain conditions,
guest fpu state to find its way into the host fpu.

Avi Kivity (1):
KVM: Prevent guest fpu state from leaking into the host

drivers/kvm/kvm.h | 3 +++
drivers/kvm/kvm_main.c | 22 ++++++++++++++++++++++
drivers/kvm/vmx.c | 12 +++---------
3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 1c040d8..152312c 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -304,6 +304,7 @@ struct kvm_vcpu {
char *host_fx_image;
char *guest_fx_image;
int fpu_active;
+ int guest_fpu_loaded;

int mmio_needed;
int mmio_read_completed;
@@ -508,6 +509,8 @@ void fx_init(struct kvm_vcpu *vcpu);
void load_msrs(struct vmx_msr_entry *e, int n);
void save_msrs(struct vmx_msr_entry *e, int n);
void kvm_resched(struct kvm_vcpu *vcpu);
+void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
+void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);

int kvm_read_guest(struct kvm_vcpu *vcpu,
gva_t addr,
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index da985b3..8f1f07a 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -253,6 +253,28 @@ int kvm_write_guest(struct kvm_vcpu *vcpu, gva_t addr, unsigned long size,
}
EXPORT_SYMBOL_GPL(kvm_write_guest);

+void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
+{
+ if (!vcpu->fpu_active || vcpu->guest_fpu_loaded)
+ return;
+
+ vcpu->guest_fpu_loaded = 1;
+ fx_save(vcpu->host_fx_image);
+ fx_restore(vcpu->guest_fx_image);
+}
+EXPORT_SYMBOL_GPL(kvm_load_guest_fpu);
+
+void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
+{
+ if (!vcpu->guest_fpu_loaded)
+ return;
+
+ vcpu->guest_fpu_loaded = 0;
+ fx_save(vcpu->guest_fx_image);
+ fx_restore(vcpu->host_fx_image);
+}
+EXPORT_SYMBOL_GPL(kvm_put_guest_fpu);
+
/*
* Switches to specified vcpu, until a matching vcpu_put()
*/
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 184238e..c1ac106 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -280,6 +280,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu)

static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
{
+ kvm_put_guest_fpu(vcpu);
put_cpu();
}

@@ -1847,10 +1848,8 @@ again:
if (vcpu->guest_debug.enabled)
kvm_guest_debug_pre(vcpu);

- if (vcpu->fpu_active) {
- fx_save(vcpu->host_fx_image);
- fx_restore(vcpu->guest_fx_image);
- }
+ kvm_load_guest_fpu(vcpu);
+
/*
* Loading guest fpu may have cleared host cr0.ts
*/
@@ -2012,11 +2011,6 @@ again:
}
#endif

- if (vcpu->fpu_active) {
- fx_save(vcpu->guest_fx_image);
- fx_restore(vcpu->host_fx_image);
- }
-
vcpu->interrupt_window_open = (vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & 3) == 0;

asm ("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));

2007-06-15 14:36:21

by David Brown

Subject: Re: [kvm-devel] [GIT PULL] KVM fix for 2.6.22

On 6/15/07, Avi Kivity <[email protected]> wrote:
> Linus,
>
> Please pull from the repository and branch at
>
> git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm.git for-linus
>
> to get a fix for a fairly critical bug which allows, under certain conditions,
> guest fpu state to find its way into the host fpu.
>
> Avi Kivity (1):
> KVM: Prevent guest fpu state from leaking into the host
>
> drivers/kvm/kvm.h | 3 +++
> drivers/kvm/kvm_main.c | 22 ++++++++++++++++++++++
> drivers/kvm/vmx.c | 12 +++---------
> 3 files changed, 28 insertions(+), 9 deletions(-)
>

Yes thank you for the fix Avi. btw what version of kvm is in 2.6.22?
the kvm wiki doesn't say.

Thanks,
- David Brown

2007-06-16 07:47:36

by Avi Kivity

Subject: Re: [kvm-devel] [GIT PULL] KVM fix for 2.6.22

David Brown wrote:
>
> Yes thank you for the fix Avi. btw what version of kvm is in 2.6.22?
> the kvm wiki doesn't say.
>

It's somewhere between kvm-21 and kvm-22. Any recent version of the
userspace can be used to drive it (i.e. starting with 2.6.22, there is
no need to match kernel and userspace versions).

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.