linux-kernel - [PATCH v2 1/2] KVM: VMX: Sanitize VM-Entry/VM-Exit control pairs at kvm

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Message-Id: <20220527170658.3571367-2-seanjc@google.com>
Date:   Fri, 27 May 2022 17:06:57 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chenyi Qiang <chenyi.qiang@...el.com>,
        Lei Wang <lei4.wang@...el.com>
Subject: [PATCH v2 1/2] KVM: VMX: Sanitize VM-Entry/VM-Exit control pairs at
 kvm_intel load time

Sanitize the VM-Entry/VM-Exit control pairs (load+load or load+clear)
during setup instead of checking both controls in a pair at runtime.  If
only one control is supported, KVM will report the associated feature as
not available, but will leave the supported control bit set in the VMCS
config, which could lead to corruption of host state.  E.g. if only the
VM-Entry control is supported and the feature is not dynamically toggled,
KVM will set the control in all VMCSes and load zeros without restoring
host state.

Note, while this is technically a bug fix, practically speaking no sane
CPU or VMM would support only one control.  KVM's behavior of checking
both controls is mostly pedantry.

Cc: Chenyi Qiang <chenyi.qiang@...el.com>
Cc: Lei Wang <lei4.wang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/capabilities.h | 13 ++++---------
 arch/x86/kvm/vmx/vmx.c          | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index dc2cb8a16e76..464bf39e4835 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -97,20 +97,17 @@ static inline bool cpu_has_vmx_posted_intr(void)
 
 static inline bool cpu_has_load_ia32_efer(void)
 {
-	return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_EFER) &&
-	       (vmcs_config.vmexit_ctrl & VM_EXIT_LOAD_IA32_EFER);
+	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_EFER;
 }
 
 static inline bool cpu_has_load_perf_global_ctrl(void)
 {
-	return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL) &&
-	       (vmcs_config.vmexit_ctrl & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL);
+	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
 }
 
 static inline bool cpu_has_vmx_mpx(void)
 {
-	return (vmcs_config.vmexit_ctrl & VM_EXIT_CLEAR_BNDCFGS) &&
-		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS);
+	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS;
 }
 
 static inline bool cpu_has_vmx_tpr_shadow(void)
@@ -377,7 +374,6 @@ static inline bool cpu_has_vmx_intel_pt(void)
 	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
 	return (vmx_msr & MSR_IA32_VMX_MISC_INTEL_PT) &&
 		(vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_PT_USE_GPA) &&
-		(vmcs_config.vmexit_ctrl & VM_EXIT_CLEAR_IA32_RTIT_CTL) &&
 		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_RTIT_CTL);
 }
 
@@ -406,8 +402,7 @@ static inline bool vmx_pebs_supported(void)
 
 static inline bool cpu_has_vmx_arch_lbr(void)
 {
-	return (vmcs_config.vmexit_ctrl & VM_EXIT_CLEAR_IA32_LBR_CTL) &&
-		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_LBR_CTL);
+	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_LBR_CTL;
 }
 
 static inline u64 vmx_get_perf_capabilities(void)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6927f6e8ec31..a592b424fbbc 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2473,6 +2473,24 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	u64 _cpu_based_3rd_exec_control = 0;
 	u32 _vmexit_control = 0;
 	u32 _vmentry_control = 0;
+	int i;
+
+	/*
+	 * LOAD/SAVE_DEBUG_CONTROLS are absent because both are mandatory.
+	 * SAVE_IA32_PAT and SAVE_IA32_EFER are absent because KVM always
+	 * intercepts writes to PAT and EFER, i.e. never enables those controls.
+	 */
+	struct {
+		u32 entry_control;
+		u32 exit_control;
+	} const vmcs_entry_exit_pairs[] = {
+		{ VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL,	VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL },
+		{ VM_ENTRY_LOAD_IA32_PAT,		VM_EXIT_LOAD_IA32_PAT },
+		{ VM_ENTRY_LOAD_IA32_EFER,		VM_EXIT_LOAD_IA32_EFER },
+		{ VM_ENTRY_LOAD_BNDCFGS,		VM_EXIT_CLEAR_BNDCFGS },
+		{ VM_ENTRY_LOAD_IA32_RTIT_CTL,		VM_EXIT_CLEAR_IA32_RTIT_CTL },
+		{ VM_ENTRY_LOAD_IA32_LBR_CTL,		VM_EXIT_CLEAR_IA32_LBR_CTL },
+	};
 
 	memset(vmcs_conf, 0, sizeof(*vmcs_conf));
 	min = CPU_BASED_HLT_EXITING |
@@ -2614,6 +2632,20 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 				&_vmentry_control) < 0)
 		return -EIO;
 
+	for (i = 0; i < ARRAY_SIZE(vmcs_entry_exit_pairs); i++) {
+		u32 n_ctrl = vmcs_entry_exit_pairs[i].entry_control;
+		u32 x_ctrl = vmcs_entry_exit_pairs[i].exit_control;
+
+		if (!(_vmentry_control & n_ctrl) == !(_vmexit_control & x_ctrl))
+			continue;
+
+		pr_warn_once("Inconsistent VM-Entry/VM-Exit pair, entry = %x, exit = %x\n",
+			     _vmentry_control & n_ctrl, _vmexit_control & x_ctrl);
+
+		_vmentry_control &= ~n_ctrl;
+		_vmexit_control &= ~x_ctrl;
+	}
+
 	/*
 	 * Some cpus support VM_{ENTRY,EXIT}_IA32_PERF_GLOBAL_CTRL but they
 	 * can't be used due to an errata where VM Exit may incorrectly clear
-- 
2.36.1.255.ge46751e96f-goog