linux-kernel - [PATCH 5.2 072/215] kvm: vmx: fix limit checking in get_vmx_mem

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Message-Id: <20190729190752.688030281@linuxfoundation.org>
Date:   Mon, 29 Jul 2019 21:21:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eugene Korenevsky <ekorenevsky@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.2 072/215] kvm: vmx: fix limit checking in get_vmx_mem_address()

[ 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 â€“ 1)
- A doubleword at an offset greater than the (effective-limit â€“ 3)
- A quadword at an offset greater than the (effective-limit â€“ 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@...il.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 b101127e13b6..543d7d82479b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4120,7 +4120,7 @@ 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