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

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Date:   Mon, 11 Jan 2021 14:02:47 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+e87846c48bf72bc85311@...kaller.appspotmail.com,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.10 143/145] KVM: x86: fix shift out of bounds reported by UBSAN

From: Paolo Bonzini <pbonzini@...hat.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@...kaller.appspotmail.com
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);