Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)")
introduced a check to prevent potential kernel memory corruption in case
the vcpu id is too great.
Unfortunately this check assumes vcpu ids grow in sequence with a common
difference of 1, which is wrong: archs are free to use vcpu id as they fit.
For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv
mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is
1024, guests may be limited down to 128 vcpus on POWER8.
This means the check does not belong here and should be moved to some arch
specific function: kvm_arch_vcpu_create() looks like a good candidate.
ARM and s390 already have such a check.
I could not spot any path in the PowerPC or common KVM code where a vcpu
id is used as described in the above commit: I believe PowerPC can live
without this check.
In the end, this patch simply moves the check to MIPS and x86.
Signed-off-by: Greg Kurz <[email protected]>
---
arch/mips/kvm/mips.c | 3 +++
arch/x86/kvm/x86.c | 3 +++
virt/kvm/kvm_main.c | 3 ---
3 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 70ef1a43c114..ce3f1e8a8b3f 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -251,6 +251,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
+ if (id >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
if (!vcpu) {
err = -ENOMEM;
goto out;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9b7798c7b210..f705d57b12ed 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7358,6 +7358,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
{
struct kvm_vcpu *vcpu;
+ if (id >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
printk_once(KERN_WARNING
"kvm: SMP vm created on host with unstable TSC; "
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4fd482fb9260..6b6cca3cb488 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2272,9 +2272,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
int r;
struct kvm_vcpu *vcpu;
- if (id >= KVM_MAX_VCPUS)
- return -EINVAL;
-
vcpu = kvm_arch_vcpu_create(kvm, id);
if (IS_ERR(vcpu))
return PTR_ERR(vcpu);
Hi Greg,
On Wed, Apr 20, 2016 at 05:07:58PM +0200, Greg Kurz wrote:
> Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)")
> introduced a check to prevent potential kernel memory corruption in case
> the vcpu id is too great.
>
> Unfortunately this check assumes vcpu ids grow in sequence with a common
> difference of 1, which is wrong: archs are free to use vcpu id as they fit.
> For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv
> mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is
> 1024, guests may be limited down to 128 vcpus on POWER8.
>
> This means the check does not belong here and should be moved to some arch
> specific function: kvm_arch_vcpu_create() looks like a good candidate.
>
> ARM and s390 already have such a check.
>
> I could not spot any path in the PowerPC or common KVM code where a vcpu
> id is used as described in the above commit: I believe PowerPC can live
> without this check.
>
> In the end, this patch simply moves the check to MIPS and x86.
>
> Signed-off-by: Greg Kurz <[email protected]>
> ---
> arch/mips/kvm/mips.c | 3 +++
> arch/x86/kvm/x86.c | 3 +++
> virt/kvm/kvm_main.c | 3 ---
> 3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index 70ef1a43c114..ce3f1e8a8b3f 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -251,6 +251,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
>
> struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
>
> + if (id >= KVM_MAX_VCPUS)
> + return -EINVAL;
This needs to go before the kzalloc above, otherwise you introduce a
memory leak.
Cheers
James
> +
> if (!vcpu) {
> err = -ENOMEM;
> goto out;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9b7798c7b210..f705d57b12ed 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7358,6 +7358,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
> {
> struct kvm_vcpu *vcpu;
>
> + if (id >= KVM_MAX_VCPUS)
> + return -EINVAL;
> +
> if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
> printk_once(KERN_WARNING
> "kvm: SMP vm created on host with unstable TSC; "
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4fd482fb9260..6b6cca3cb488 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2272,9 +2272,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> int r;
> struct kvm_vcpu *vcpu;
>
> - if (id >= KVM_MAX_VCPUS)
> - return -EINVAL;
> -
> vcpu = kvm_arch_vcpu_create(kvm, id);
> if (IS_ERR(vcpu))
> return PTR_ERR(vcpu);
>
On Wed, 20 Apr 2016 16:12:46 +0100
James Hogan <[email protected]> wrote:
> Hi Greg,
>
> On Wed, Apr 20, 2016 at 05:07:58PM +0200, Greg Kurz wrote:
> > Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)")
> > introduced a check to prevent potential kernel memory corruption in case
> > the vcpu id is too great.
> >
> > Unfortunately this check assumes vcpu ids grow in sequence with a common
> > difference of 1, which is wrong: archs are free to use vcpu id as they fit.
> > For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv
> > mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is
> > 1024, guests may be limited down to 128 vcpus on POWER8.
> >
> > This means the check does not belong here and should be moved to some arch
> > specific function: kvm_arch_vcpu_create() looks like a good candidate.
> >
> > ARM and s390 already have such a check.
> >
> > I could not spot any path in the PowerPC or common KVM code where a vcpu
> > id is used as described in the above commit: I believe PowerPC can live
> > without this check.
> >
> > In the end, this patch simply moves the check to MIPS and x86.
> >
> > Signed-off-by: Greg Kurz <[email protected]>
> > ---
> > arch/mips/kvm/mips.c | 3 +++
> > arch/x86/kvm/x86.c | 3 +++
> > virt/kvm/kvm_main.c | 3 ---
> > 3 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > index 70ef1a43c114..ce3f1e8a8b3f 100644
> > --- a/arch/mips/kvm/mips.c
> > +++ b/arch/mips/kvm/mips.c
> > @@ -251,6 +251,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
> >
> > struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
> >
> > + if (id >= KVM_MAX_VCPUS)
> > + return -EINVAL;
>
> This needs to go before the kzalloc above, otherwise you introduce a
> memory leak.
>
Oops you're right.. my bad. I'll post a v2 right away.
Thanks !
--
Greg
> Cheers
> James
>
> > +
> > if (!vcpu) {
> > err = -ENOMEM;
> > goto out;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 9b7798c7b210..f705d57b12ed 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7358,6 +7358,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
> > {
> > struct kvm_vcpu *vcpu;
> >
> > + if (id >= KVM_MAX_VCPUS)
> > + return -EINVAL;
> > +
> > if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
> > printk_once(KERN_WARNING
> > "kvm: SMP vm created on host with unstable TSC; "
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 4fd482fb9260..6b6cca3cb488 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2272,9 +2272,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> > int r;
> > struct kvm_vcpu *vcpu;
> >
> > - if (id >= KVM_MAX_VCPUS)
> > - return -EINVAL;
> > -
> > vcpu = kvm_arch_vcpu_create(kvm, id);
> > if (IS_ERR(vcpu))
> > return PTR_ERR(vcpu);
> >
Hi,
[auto build test WARNING on kvm/linux-next]
[also build test WARNING on v4.6-rc4 next-20160420]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
url: https://github.com/0day-ci/linux/commits/Greg-Kurz/KVM-remove-buggy-vcpu-id-check-on-vcpu-creation/20160420-231233
base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
config: x86_64-randconfig-x017-201616 (attached as .config)
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64
All warnings (new ones prefixed by >>):
arch/x86/kvm/x86.c: In function 'kvm_arch_vcpu_create':
>> arch/x86/kvm/x86.c:7362:10: warning: return makes pointer from integer without a cast [-Wint-conversion]
return -EINVAL;
^
vim +7362 arch/x86/kvm/x86.c
7346 }
7347
7348 void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
7349 {
7350 kvmclock_reset(vcpu);
7351
7352 free_cpumask_var(vcpu->arch.wbinvd_dirty_mask);
7353 kvm_x86_ops->vcpu_free(vcpu);
7354 }
7355
7356 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
7357 unsigned int id)
7358 {
7359 struct kvm_vcpu *vcpu;
7360
7361 if (id >= KVM_MAX_VCPUS)
> 7362 return -EINVAL;
7363
7364 if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
7365 printk_once(KERN_WARNING
7366 "kvm: SMP vm created on host with unstable TSC; "
7367 "guest TSC will not be reliable\n");
7368
7369 vcpu = kvm_x86_ops->vcpu_create(kvm, id);
7370
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation