[PATCH 4.19 77/77] KVM: x86: fix shift out of bounds reported by UBSAN

[Greg Kroah-Hartman]

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -53,7 +53,7 @@ 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_mask, u64 mmio_value);