linux-kernel - [PATCH 2/2] KVM: SVM: Require nrips support for SEV guests (and beyond)

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Date:   Thu, 10 Aug 2023 16:49:18 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wu Zongyo <wuzongyo@...l.ustc.edu.cn>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 2/2] KVM: SVM: Require nrips support for SEV guests (and beyond)

Disallow SEV (and beyond) if nrips is disabled via module param, as KVM
can't read guest memory to partially emulate and skip an instruction.  All
CPUs that support SEV support NRIPS, i.e. this is purely stopping the user
from shooting themselves in the foot.

Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/sev.c |  2 +-
 arch/x86/kvm/svm/svm.c | 11 ++++-------
 arch/x86/kvm/svm/svm.h |  1 +
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 2cd15783dfb9..8ce9ffc8709e 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2185,7 +2185,7 @@ void __init sev_hardware_setup(void)
 	bool sev_es_supported = false;
 	bool sev_supported = false;
 
-	if (!sev_enabled || !npt_enabled)
+	if (!sev_enabled || !npt_enabled || !nrips)
 		goto out;
 
 	/*
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 581958c9dd4d..7cb5ef5835c2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -202,7 +202,7 @@ static int nested = true;
 module_param(nested, int, S_IRUGO);
 
 /* enable/disable Next RIP Save */
-static int nrips = true;
+int nrips = true;
 module_param(nrips, int, 0444);
 
 /* enable/disable Virtual VMLOAD VMSAVE */
@@ -5191,9 +5191,11 @@ static __init int svm_hardware_setup(void)
 
 	svm_adjust_mmio_mask();
 
+	nrips = nrips && boot_cpu_has(X86_FEATURE_NRIPS);
+
 	/*
 	 * Note, SEV setup consumes npt_enabled and enable_mmio_caching (which
-	 * may be modified by svm_adjust_mmio_mask()).
+	 * may be modified by svm_adjust_mmio_mask()), as well as nrips.
 	 */
 	sev_hardware_setup();
 
@@ -5205,11 +5207,6 @@ static __init int svm_hardware_setup(void)
 			goto err;
 	}
 
-	if (nrips) {
-		if (!boot_cpu_has(X86_FEATURE_NRIPS))
-			nrips = false;
-	}
-
 	enable_apicv = avic = avic && avic_hardware_setup();
 
 	if (!enable_apicv) {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 2237230aad98..860511276087 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -34,6 +34,7 @@
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
+extern int nrips;
 extern int vgif;
 extern bool intercept_smi;
 extern bool x2avic_enabled;
-- 
2.41.0.694.ge786442a9b-goog