[PATCH AUTOSEL 5.1 053/141] kvm: vmx: fix limit checking in get_vmx_mem_address()

Sasha Levin
2019-07-19T04:04:41Z

From: Eugene Korenevsky <ekorenevsky@gmail.com>

[ Upstream commit c1a9acbc5295e278d788e9f7510f543bc9864fa2 ]

Intel SDM vol. 3, 5.3:
The processor causes a
general-protection exception (or, if the segment is SS, a stack-fault
exception) any time an attempt is made to access the following addresses
in a segment:
- A byte at an offset greater than the effective limit
- A word at an offset greater than the (effective-limit – 1)
- A doubleword at an offset greater than the (effective-limit – 3)
- A quadword at an offset greater than the (effective-limit – 7)

Therefore, the generic limit checking error condition must be

exn = (off > limit + 1 - access_len) = (off + access_len - 1 > limit)

but not

exn = (off + access_len > limit)

as for now.

Also avoid integer overflow of `off` at 32-bit KVM by casting it to u64.

Note: access length is currently sizeof(u64) which is incorrect. This
will be fixed in the subsequent patch.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/vmx/nested.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4ca834d22169..897ae4b62980 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4143,7 +4143,7 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
*/
if (!(s.base == 0 && s.limit == 0xffffffff &&
((s.type & 8) || !(s.type & 4))))
- exn = exn || (off + sizeof(u64) > s.limit);
+ exn = exn || ((u64)off + sizeof(u64) - 1 > s.limit);
}
if (exn) {
kvm_queue_exception_e(vcpu,
--
2.20.1