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Subject[PATCH 19/19] KVM: MMU: Fix potential race setting upper shadow ptes on nonpae hosts
Date
The direct mapped shadow code (used for real mode and two dimensional paging)
sets upper-level ptes using direct assignment rather than calling
set_shadow_pte(). A nonpae host will split this into two writes, which opens
up a race if another vcpu accesses the same memory area.

Fix by calling set_shadow_pte() instead of assigning directly.

Noticed by Izik Eidus.

Signed-off-by: Avi Kivity <avi@qumranet.com>
---
arch/x86/kvm/mmu.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7f57da6..b0e4ddc 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1189,9 +1189,10 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
return -ENOMEM;
}

- table[index] = __pa(new_table->spt)
- | PT_PRESENT_MASK | PT_WRITABLE_MASK
- | shadow_user_mask | shadow_x_mask;
+ set_shadow_pte(&table[index],
+ __pa(new_table->spt)
+ | PT_PRESENT_MASK | PT_WRITABLE_MASK
+ | shadow_user_mask | shadow_x_mask);
}
table_addr = table[index] & PT64_BASE_ADDR_MASK;
}
--
1.5.6.1


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