From 6b8d0f9b180cb93513bb65f705b299370f0357a1 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Wed, 18 Apr 2007 11:18:18 +0300 Subject: [PATCH] KVM: Fix off-by-one when writing to a nonpae guest pde Nonpae guest pdes are shadowed by two pae ptes, so we double the offset twice: once to account for the pte size difference, and once because we need to shadow pdes for a single guest pde. But when writing to the upper guest pde we also need to truncate the lower bits, otherwise the multiply shifts these bits into the pde index and causes an access to the wrong shadow pde. If we're at the end of the page (accessing the very last guest pde) we can even overflow into the next host page and oops. Signed-off-by: Avi Kivity --- drivers/kvm/mmu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c index e85b4c7c36f7..cab26f301eab 100644 --- a/drivers/kvm/mmu.c +++ b/drivers/kvm/mmu.c @@ -1171,6 +1171,7 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes) * and zap two pdes instead of one. */ if (level == PT32_ROOT_LEVEL) { + page_offset &= ~7; /* kill rounding error */ page_offset <<= 1; npte = 2; } -- 2.20.1