[PATCH 5.10 143/145] KVM: x86: fix shift out of bounds reported by UBSAN

Greg Kroah-Hartman
2021-01-11T13:19:48Z

From: Paolo Bonzini <pbonzini@redhat.com>

commit 2f80d502d627f30257ba7e3655e71c373b7d1a5a upstream.

Since we know that e >= s, we can reassociate the left shift,
changing the shifted number from 1 to 2 in exchange for
decreasing the right hand side by 1.

Reported-by: syzbot+e87846c48bf72bc85311@syzkaller.appspotmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/mmu.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -49,7 +49,7 @@ static inline u64 rsvd_bits(int s, int e
if (e < s)
return 0;

- return ((1ULL << (e - s + 1)) - 1) << s;
+ return ((2ULL << (e - s)) - 1) << s;
}

void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 access_mask);