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Message-ID: <1366602889.3408.144.camel@deadeye.wl.decadent.org.uk>
Date: Mon, 22 Apr 2013 04:54:49 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: Luis Henriques <luis.henriques@...onical.com>
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 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.
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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