linux-kernel - [PATCH 04/19] kvm: x86: Check guest xstate permissions when KVM_SET

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Date:   Tue,  7 Dec 2021 19:03:44 -0500
From:   Yang Zhong <yang.zhong@...el.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        yang.zhong@...el.com
Subject: [PATCH 04/19] kvm: x86: Check guest xstate permissions when KVM_SET_CPUID2

From: Jing Liu <jing2.liu@...el.com>

Guest xstate permissions should be set by userspace VMM before vcpu
creation. This patch extends KVM to check the guest permissions in
KVM_SET_CPUID2 ioctl to avoid permission failure at guest run-time
(e.g. when reallocation path is triggered).

Signed-off-by: Jing Liu <jing2.liu@...el.com>
Signed-off-by: Yang Zhong <yang.zhong@...el.com>
---
 arch/x86/kvm/cpuid.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 148003e26cbb..f3c61205bbf4 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -18,6 +18,7 @@
 #include <asm/processor.h>
 #include <asm/user.h>
 #include <asm/fpu/xstate.h>
+#include <asm/fpu/api.h>
 #include <asm/sgx.h>
 #include "cpuid.h"
 #include "lapic.h"
@@ -97,6 +98,17 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
 			return -EINVAL;
 	}
 
+	/*
+	 * Check guest permissions for XSTATE features which must
+	 * be enabled dynamically.
+	 */
+	best = cpuid_entry2_find(entries, nent, 7, 0);
+	if (best && cpuid_entry_has(best, X86_FEATURE_AMX_TILE)) {
+		if (!(xstate_get_guest_group_perm() &
+			XFEATURE_MASK_XTILE_DATA))
+			return -EINVAL;
+	}
+
 	return 0;
 }