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Date: Mon, 22 Apr 2013 09:55:51 +0100
From: Luis Henriques <luis.henriques@...onical.com>
To: Ben Hutchings <ben@...adent.org.uk>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com, Andrew Honig <ahonig@...gle.com>,
Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 35/72] KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use
gfn_to_hva_cache functions (CVE-2013-1797)
On Mon, Apr 22, 2013 at 04:54:49AM +0100, Ben Hutchings wrote:
> On Thu, 2013-04-18 at 10:16 +0100, Luis Henriques wrote:
> > 3.5.7.11 -stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Andy Honig <ahonig@...gle.com>
> >
> > commit 0b79459b482e85cb7426aa7da683a9f2c97aeae1 upstream.
> >
> > There is a potential use after free issue with the handling of
> > MSR_KVM_SYSTEM_TIME. If the guest specifies a GPA in a movable or removable
> > memory such as frame buffers then KVM might continue to write to that
> > address even after it's removed via KVM_SET_USER_MEMORY_REGION. KVM pins
> > the page in memory so it's unlikely to cause an issue, but if the user
> > space component re-purposes the memory previously used for the guest, then
> > the guest will be able to corrupt that memory.
> >
> > Tested: Tested against kvmclock unit test
> >
> > Signed-off-by: Andrew Honig <ahonig@...gle.com>
> > Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
> > [ luis: backported to 3.5:
> > - Adjust context
> > - Removed references to PVCLOCK_GUEST_STOPPED ]
> > Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
>
> This apparently needs to be followed by commit 8f964525a121 'KVM: Allow
> cross page reads and writes from cached translations.', as some guests
> don't follow the rules.
Thanks Ben, I'll add it to the queue.
Cheers,
--
Luis
>
> Ben.
>
> > ---
> > arch/x86/include/asm/kvm_host.h | 4 ++--
> > arch/x86/kvm/x86.c | 40 +++++++++++++++-------------------------
> > 2 files changed, 17 insertions(+), 27 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index db7c1f2..9a50912 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -410,8 +410,8 @@ struct kvm_vcpu_arch {
> > gpa_t time;
> > struct pvclock_vcpu_time_info hv_clock;
> > unsigned int hw_tsc_khz;
> > - unsigned int time_offset;
> > - struct page *time_page;
> > + struct gfn_to_hva_cache pv_time;
> > + bool pv_time_enabled;
> >
> > struct {
> > u64 msr_val;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ad5cf4b..5b4ac78 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1118,7 +1118,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> > {
> > unsigned long flags;
> > struct kvm_vcpu_arch *vcpu = &v->arch;
> > - void *shared_kaddr;
> > unsigned long this_tsc_khz;
> > s64 kernel_ns, max_kernel_ns;
> > u64 tsc_timestamp;
> > @@ -1154,7 +1153,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> >
> > local_irq_restore(flags);
> >
> > - if (!vcpu->time_page)
> > + if (!vcpu->pv_time_enabled)
> > return 0;
> >
> > /*
> > @@ -1212,14 +1211,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> > */
> > vcpu->hv_clock.version += 2;
> >
> > - shared_kaddr = kmap_atomic(vcpu->time_page);
> > -
> > - memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock,
> > - sizeof(vcpu->hv_clock));
> > -
> > - kunmap_atomic(shared_kaddr);
> > -
> > - mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT);
> > + kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
> > + &vcpu->hv_clock,
> > + sizeof(vcpu->hv_clock));
> > return 0;
> > }
> >
> > @@ -1508,10 +1502,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> >
> > static void kvmclock_reset(struct kvm_vcpu *vcpu)
> > {
> > - if (vcpu->arch.time_page) {
> > - kvm_release_page_dirty(vcpu->arch.time_page);
> > - vcpu->arch.time_page = NULL;
> > - }
> > + vcpu->arch.pv_time_enabled = false;
> > }
> >
> > static void accumulate_steal_time(struct kvm_vcpu *vcpu)
> > @@ -1606,6 +1597,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> > break;
> > case MSR_KVM_SYSTEM_TIME_NEW:
> > case MSR_KVM_SYSTEM_TIME: {
> > + u64 gpa_offset;
> > kvmclock_reset(vcpu);
> >
> > vcpu->arch.time = data;
> > @@ -1615,21 +1607,18 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> > if (!(data & 1))
> > break;
> >
> > - /* ...but clean it before doing the actual write */
> > - vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
> > + gpa_offset = data & ~(PAGE_MASK | 1);
> >
> > /* Check that the address is 32-byte aligned. */
> > - if (vcpu->arch.time_offset &
> > - (sizeof(struct pvclock_vcpu_time_info) - 1))
> > + if (gpa_offset & (sizeof(struct pvclock_vcpu_time_info) - 1))
> > break;
> >
> > - vcpu->arch.time_page =
> > - gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);
> > + if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
> > + &vcpu->arch.pv_time, data & ~1ULL))
> > + vcpu->arch.pv_time_enabled = false;
> > + else
> > + vcpu->arch.pv_time_enabled = true;
> >
> > - if (is_error_page(vcpu->arch.time_page)) {
> > - kvm_release_page_clean(vcpu->arch.time_page);
> > - vcpu->arch.time_page = NULL;
> > - }
> > break;
> > }
> > case MSR_KVM_ASYNC_PF_EN:
> > @@ -2616,7 +2605,7 @@ static int kvm_vcpu_ioctl_x86_set_xcrs(struct kvm_vcpu *vcpu,
> > static int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
> > {
> > struct pvclock_vcpu_time_info *src = &vcpu->arch.hv_clock;
> > - if (!vcpu->arch.time_page)
> > + if (!vcpu->arch.pv_time_enabled)
> > return -EINVAL;
> > src->flags |= PVCLOCK_GUEST_STOPPED;
> > mark_page_dirty(vcpu->kvm, vcpu->arch.time >> PAGE_SHIFT);
> > @@ -6216,6 +6205,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> > if (!zalloc_cpumask_var(&vcpu->arch.wbinvd_dirty_mask, GFP_KERNEL))
> > goto fail_free_mce_banks;
> >
> > + vcpu->arch.pv_time_enabled = false;
> > kvm_async_pf_hash_reset(vcpu);
> > kvm_pmu_init(vcpu);
> >
>
> --
> Ben Hutchings
> Klipstein's 4th Law of Prototyping and Production:
> A fail-safe circuit will destroy others.
--
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