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KVM: Check validity of offset+length of gfn_to_pfn_cache prior to activation 

When activating a gfn_to_pfn_cache, verify that the offset+length is sane
and usable before marking the cache active.  Letting __kvm_gpc_refresh()
detect the problem results in a cache being marked active without setting
the GPA (or any other fields), which in turn results in KVM trying to
refresh a cache with INVALID_GPA.

Attempting to refresh a cache with INVALID_GPA isn't functionally
problematic, but it runs afoul of the sanity check that exactly one of
GPA or userspace HVA is valid, i.e. that a cache is either GPA-based or
HVA-based.

Reported-by: syzbot+106a4f72b0474e1d1b33@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/0000000000005fa5cc0613f1cebd@google.com
Fixes: 721f5b0dda ("KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA")
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Paul Durrant <paul@xen.org>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240320001542.3203871-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-03-19 17:15:41 -07:00
parent 18f06e9769
commit 5c9ca4ed89
1 changed files with 9 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
virt/kvm/pfncache.c
View File

@ -245,8 +245,7 @@ out_error:
return -EFAULT;
}
static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
unsigned long len)
static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva)
{
unsigned long page_offset;
bool unmap_old = false;
@ -260,9 +259,6 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva)))
return -EINVAL;
if (!kvm_gpc_is_valid_len(gpa, uhva, len))
return -EINVAL;
lockdep_assert_held(&gpc->refresh_lock);
write_lock_irq(&gpc->lock);
@ -365,6 +361,9 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
guard(mutex)(&gpc->refresh_lock);
if (!kvm_gpc_is_valid_len(gpc->gpa, gpc->uhva, len))
return -EINVAL;
/*
* If the GPA is valid then ignore the HVA, as a cache can be GPA-based
* or HVA-based, not both. For GPA-based caches, the HVA will be
@ -372,7 +371,7 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
*/
uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva : KVM_HVA_ERR_BAD;
return __kvm_gpc_refresh(gpc, gpc->gpa, uhva, len);
return __kvm_gpc_refresh(gpc, gpc->gpa, uhva);
}
void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
@ -392,6 +391,9 @@ static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned
{
struct kvm *kvm = gpc->kvm;
if (!kvm_gpc_is_valid_len(gpa, uhva, len))
return -EINVAL;
guard(mutex)(&gpc->refresh_lock);
if (!gpc->active) {
@ -411,7 +413,7 @@ static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned
gpc->active = true;
write_unlock_irq(&gpc->lock);
}
return __kvm_gpc_refresh(gpc, gpa, uhva, len);
return __kvm_gpc_refresh(gpc, gpa, uhva);
}
int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)