linux-kernel - [PATCH 5.4 057/111] KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c

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Date:   Tue, 26 May 2020 20:53:15 +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, Jim Mattson <jmattson@...gle.com>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.4 057/111] KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c

From: Babu Moger <babu.moger@....com>

commit 37486135d3a7b03acc7755b63627a130437f066a upstream.

Though rdpkru and wrpkru are contingent upon CR4.PKE, the PKRU
resource isn't. It can be read with XSAVE and written with XRSTOR.
So, if we don't set the guest PKRU value here(kvm_load_guest_xsave_state),
the guest can read the host value.

In case of kvm_load_host_xsave_state, guest with CR4.PKE clear could
potentially use XRSTOR to change the host PKRU value.

While at it, move pkru state save/restore to common code and the
host_pkru field to kvm_vcpu_arch.  This will let SVM support protection keys.

Cc: stable@...r.kernel.org
Reported-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Babu Moger <babu.moger@....com>
Message-Id: <158932794619.44260.14508381096663848853.stgit@...les-babu.amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/asm/kvm_host.h |    1 +
 arch/x86/kvm/vmx/vmx.c          |   18 ------------------
 arch/x86/kvm/x86.c              |   17 +++++++++++++++++
 3 files changed, 18 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -550,6 +550,7 @@ struct kvm_vcpu_arch {
 	unsigned long cr4;
 	unsigned long cr4_guest_owned_bits;
 	unsigned long cr8;
+	u32 host_pkru;
 	u32 pkru;
 	u32 hflags;
 	u64 efer;
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1360,7 +1360,6 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu
 
 	vmx_vcpu_pi_load(vcpu, cpu);
 
-	vmx->host_pkru = read_pkru();
 	vmx->host_debugctlmsr = get_debugctlmsr();
 }
 
@@ -6521,11 +6520,6 @@ static void vmx_vcpu_run(struct kvm_vcpu
 
 	kvm_load_guest_xcr0(vcpu);
 
-	if (static_cpu_has(X86_FEATURE_PKU) &&
-	    kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
-	    vcpu->arch.pkru != vmx->host_pkru)
-		__write_pkru(vcpu->arch.pkru);
-
 	pt_guest_enter(vmx);
 
 	atomic_switch_perf_msrs(vmx);
@@ -6614,18 +6608,6 @@ static void vmx_vcpu_run(struct kvm_vcpu
 
 	pt_guest_exit(vmx);
 
-	/*
-	 * eager fpu is enabled if PKEY is supported and CR4 is switched
-	 * back on host, so it is safe to read guest PKRU from current
-	 * XSAVE.
-	 */
-	if (static_cpu_has(X86_FEATURE_PKU) &&
-	    kvm_read_cr4_bits(vcpu, X86_CR4_PKE)) {
-		vcpu->arch.pkru = rdpkru();
-		if (vcpu->arch.pkru != vmx->host_pkru)
-			__write_pkru(vmx->host_pkru);
-	}
-
 	kvm_put_guest_xcr0(vcpu);
 
 	vmx->nested.nested_run_pending = 0;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -832,11 +832,25 @@ void kvm_load_guest_xcr0(struct kvm_vcpu
 			xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
 		vcpu->guest_xcr0_loaded = 1;
 	}
+
+	if (static_cpu_has(X86_FEATURE_PKU) &&
+	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
+	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)) &&
+	    vcpu->arch.pkru != vcpu->arch.host_pkru)
+		__write_pkru(vcpu->arch.pkru);
 }
 EXPORT_SYMBOL_GPL(kvm_load_guest_xcr0);
 
 void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
 {
+	if (static_cpu_has(X86_FEATURE_PKU) &&
+	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
+	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {
+		vcpu->arch.pkru = rdpkru();
+		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
+			__write_pkru(vcpu->arch.host_pkru);
+	}
+
 	if (vcpu->guest_xcr0_loaded) {
 		if (vcpu->arch.xcr0 != host_xcr0)
 			xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
@@ -8222,6 +8236,9 @@ static int vcpu_enter_guest(struct kvm_v
 	trace_kvm_entry(vcpu->vcpu_id);
 	guest_enter_irqoff();
 
+	/* Save host pkru register if supported */
+	vcpu->arch.host_pkru = read_pkru();
+
 	fpregs_assert_state_consistent();
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		switch_fpu_return();