2021-02-08 18:47:28

by Peter Gonda

Subject: [PATCH for 4.19] Fix unsynchronized access to sev members through svm_register_enc_region

commit 19a23da53932bc8011220bd8c410cb76012de004 upstream.

Grab kvm->lock before pinning memory when registering an encrypted
region; sev_pin_memory() relies on kvm->lock being held to ensure
correctness when checking and updating the number of pinned pages.

Add a lockdep assertion to help prevent future regressions.

Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Brijesh Singh <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Fixes: 1e80fdc09d12 ("KVM: SVM: Pin guest memory when SEV is active")
Signed-off-by: Peter Gonda <[email protected]>

V2
- Fix up patch description
- Correct file paths svm.c -> sev.c
- Add unlock of kvm->lock on sev_pin_memory error

V1
- https://lore.kernel.org/kvm/[email protected]/

Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
arch/x86/kvm/svm.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 2b506904be02..93c89f1ffc5d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1830,6 +1830,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
struct page **pages;
unsigned long first, last;

+ lockdep_assert_held(&kvm->lock);
+
if (ulen == 0 || uaddr + ulen < uaddr)
return NULL;

@@ -7086,12 +7088,21 @@ static int svm_register_enc_region(struct kvm *kvm,
if (!region)
return -ENOMEM;

+ mutex_lock(&kvm->lock);
region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
if (!region->pages) {
ret = -ENOMEM;
+ mutex_unlock(&kvm->lock);
goto e_free;
}

+ region->uaddr = range->addr;
+ region->size = range->size;
+
+ mutex_lock(&kvm->lock);
+ list_add_tail(&region->list, &sev->regions_list);
+ mutex_unlock(&kvm->lock);
+
/*
* The guest may change the memory encryption attribute from C=0 -> C=1
* or vice versa for this memory range. Lets make sure caches are
@@ -7100,13 +7111,6 @@ static int svm_register_enc_region(struct kvm *kvm,
*/
sev_clflush_pages(region->pages, region->npages);

- region->uaddr = range->addr;
- region->size = range->size;
-
- mutex_lock(&kvm->lock);
- list_add_tail(&region->list, &sev->regions_list);
- mutex_unlock(&kvm->lock);
-
return ret;

e_free:
--
2.30.0.478.g8a0d178c01-goog

2021-02-08 18:50:14

by Paolo Bonzini

Subject: Re: [PATCH for 4.19] Fix unsynchronized access to sev members through svm_register_enc_region

On 08/02/21 17:48, Peter Gonda wrote:
> commit 19a23da53932bc8011220bd8c410cb76012de004 upstream.
>
> Grab kvm->lock before pinning memory when registering an encrypted
> region; sev_pin_memory() relies on kvm->lock being held to ensure
> correctness when checking and updating the number of pinned pages.
>
> Add a lockdep assertion to help prevent future regressions.
>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Joerg Roedel <[email protected]>
> Cc: Tom Lendacky <[email protected]>
> Cc: Brijesh Singh <[email protected]>
> Cc: Sean Christopherson <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Fixes: 1e80fdc09d12 ("KVM: SVM: Pin guest memory when SEV is active")
> Signed-off-by: Peter Gonda <[email protected]>
>
> V2
> - Fix up patch description
> - Correct file paths svm.c -> sev.c
> - Add unlock of kvm->lock on sev_pin_memory error
>
> V1
> - https://lore.kernel.org/kvm/[email protected]/
>
> Message-Id: <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> arch/x86/kvm/svm.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2b506904be02..93c89f1ffc5d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1830,6 +1830,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
> struct page **pages;
> unsigned long first, last;
>
> + lockdep_assert_held(&kvm->lock);
> +
> if (ulen == 0 || uaddr + ulen < uaddr)
> return NULL;
>
> @@ -7086,12 +7088,21 @@ static int svm_register_enc_region(struct kvm *kvm,
> if (!region)
> return -ENOMEM;
>
> + mutex_lock(&kvm->lock);
> region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
> if (!region->pages) {
> ret = -ENOMEM;
> + mutex_unlock(&kvm->lock);
> goto e_free;
> }
>
> + region->uaddr = range->addr;
> + region->size = range->size;
> +
> + mutex_lock(&kvm->lock);
> + list_add_tail(&region->list, &sev->regions_list);
> + mutex_unlock(&kvm->lock);
> +
> /*
> * The guest may change the memory encryption attribute from C=0 -> C=1
> * or vice versa for this memory range. Lets make sure caches are
> @@ -7100,13 +7111,6 @@ static int svm_register_enc_region(struct kvm *kvm,
> */
> sev_clflush_pages(region->pages, region->npages);
>
> - region->uaddr = range->addr;
> - region->size = range->size;
> -
> - mutex_lock(&kvm->lock);
> - list_add_tail(&region->list, &sev->regions_list);
> - mutex_unlock(&kvm->lock);
> -
> return ret;
>
> e_free:
>

Acked-by: Paolo Bonzini <[email protected]>