linux-kernel - [PATCH AUTOSEL 5.2 46/85] KVM: nVMX: Ignore segment base for VMX memory operand when segment not FS or GS

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Date:   Fri, 26 Jul 2019 09:38:56 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Liran Alon <liran.alon@...cle.com>,
        Maxime Villard <max@...nbsd.net>,
        Joao Martins <joao.m.martins@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org
Subject: [PATCH AUTOSEL 5.2 46/85] KVM: nVMX: Ignore segment base for VMX memory operand when segment not FS or GS

From: Liran Alon <liran.alon@...cle.com>

[ Upstream commit 6694e48012826351036fd10fc506ca880023e25f ]

As reported by Maxime at
https://bugzilla.kernel.org/show_bug.cgi?id=204175:

In vmx/nested.c::get_vmx_mem_address(), when the guest runs in long mode,
the base address of the memory operand is computed with a simple:
    *ret = s.base + off;

This is incorrect, the base applies only to FS and GS, not to the others.
Because of that, if the guest uses a VMX instruction based on DS and has
a DS.base that is non-zero, KVM wrongfully adds the base to the
resulting address.

Reported-by: Maxime Villard <max@...nbsd.net>
Reviewed-by: Joao Martins <joao.m.martins@...cle.com>
Signed-off-by: Liran Alon <liran.alon@...cle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/vmx/nested.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 46af3a5e9209..aa949ab7850c 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4068,7 +4068,10 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
 		 * mode, e.g. a 32-bit address size can yield a 64-bit virtual
 		 * address when using FS/GS with a non-zero base.
 		 */
-		*ret = s.base + off;
+		if (seg_reg == VCPU_SREG_FS || seg_reg == VCPU_SREG_GS)
+			*ret = s.base + off;
+		else
+			*ret = off;
 
 		/* Long mode: #GP(0)/#SS(0) if the memory address is in a
 		 * non-canonical form. This is the only check on the memory
-- 
2.20.1