linux-kernel - [PATCH AUTOSEL 5.4 263/330] KVM: x86: handle wrap around 32-bit address space

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Message-Id: <20200918020110.2063155-263-sashal@kernel.org>
Date:   Thu, 17 Sep 2020 22:00:03 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Nick Peterson <everdox@...il.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 263/330] KVM: x86: handle wrap around 32-bit address space

From: Paolo Bonzini <pbonzini@...hat.com>

[ Upstream commit fede8076aab4c2280c673492f8f7a2e87712e8b4 ]

KVM is not handling the case where EIP wraps around the 32-bit address
space (that is, outside long mode).  This is needed both in vmx.c
and in emulate.c.  SVM with NRIPS is okay, but it can still print
an error to dmesg due to integer overflow.

Reported-by: Nick Peterson <everdox@...il.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/emulate.c |  2 ++
 arch/x86/kvm/svm.c     |  3 ---
 arch/x86/kvm/vmx/vmx.c | 15 ++++++++++++---
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 128d3ad46e965..cc7823e7ef96c 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5836,6 +5836,8 @@ writeback:
 	}
 
 	ctxt->eip = ctxt->_eip;
+	if (ctxt->mode != X86EMUL_MODE_PROT64)
+		ctxt->eip = (u32)ctxt->_eip;
 
 done:
 	if (rc == X86EMUL_PROPAGATE_FAULT) {
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3243a80ea32c0..802b5f9ab7446 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -787,9 +787,6 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 		if (!kvm_emulate_instruction(vcpu, EMULTYPE_SKIP))
 			return 0;
 	} else {
-		if (svm->next_rip - kvm_rip_read(vcpu) > MAX_INST_SIZE)
-			pr_err("%s: ip 0x%lx next 0x%llx\n",
-			       __func__, kvm_rip_read(vcpu), svm->next_rip);
 		kvm_rip_write(vcpu, svm->next_rip);
 	}
 	svm_set_interrupt_shadow(vcpu, 0);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a071eab3bab74..14b973990d5a8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1541,7 +1541,7 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
 
 static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
-	unsigned long rip;
+	unsigned long rip, orig_rip;
 
 	/*
 	 * Using VMCS.VM_EXIT_INSTRUCTION_LEN on EPT misconfig depends on
@@ -1553,8 +1553,17 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	 */
 	if (!static_cpu_has(X86_FEATURE_HYPERVISOR) ||
 	    to_vmx(vcpu)->exit_reason != EXIT_REASON_EPT_MISCONFIG) {
-		rip = kvm_rip_read(vcpu);
-		rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
+		orig_rip = kvm_rip_read(vcpu);
+		rip = orig_rip + vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
+#ifdef CONFIG_X86_64
+		/*
+		 * We need to mask out the high 32 bits of RIP if not in 64-bit
+		 * mode, but just finding out that we are in 64-bit mode is
+		 * quite expensive.  Only do it if there was a carry.
+		 */
+		if (unlikely(((rip ^ orig_rip) >> 31) == 3) && !is_64_bit_mode(vcpu))
+			rip = (u32)rip;
+#endif
 		kvm_rip_write(vcpu, rip);
 	} else {
 		if (!kvm_emulate_instruction(vcpu, EMULTYPE_SKIP))
-- 
2.25.1