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KVM: Harden guest memory APIs against out-of-bounds accesses

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When reading or writing a guest page, WARN and bail if offset+len would
result in a read to a different page so that KVM bugs are more likely to
be detected, and so that any such bugs are less likely to escalate to an
out-of-bounds access.  E.g. if userspace isn't using guard pages and the
target page is at the end of a memslot.

Note, KVM already hardens itself in similar APIs, e.g. in the "cached"
variants, it's just the vanilla APIs that are playing with fire.

Link: https://lore.kernel.org/r/20240829191413.900740-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-08-29 12:14:13 -07:00
parent ec495f2ab1
commit 025dde582b
1 changed files with 9 additions and 0 deletions
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9
virt/kvm/kvm_main.c
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@ -3275,6 +3275,9 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
int r;
unsigned long addr;
if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
return -EFAULT;
addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
if (kvm_is_error_hva(addr))
return -EFAULT;
@ -3348,6 +3351,9 @@ static int __kvm_read_guest_atomic(struct kvm_memory_slot *slot, gfn_t gfn,
int r;
unsigned long addr;
if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
return -EFAULT;
addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
if (kvm_is_error_hva(addr))
return -EFAULT;
@ -3378,6 +3384,9 @@ static int __kvm_write_guest_page(struct kvm *kvm,
int r;
unsigned long addr;
if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
return -EFAULT;
addr = gfn_to_hva_memslot(memslot, gfn);
if (kvm_is_error_hva(addr))
return -EFAULT;