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Message-Id: <20250416002546.3300893-2-mlevitsk@redhat.com>
Date: Tue, 15 Apr 2025 20:25:44 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
Paolo Bonzini <pbonzini@...hat.com>,
x86@...nel.org,
Sean Christopherson <seanjc@...gle.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org,
"H. Peter Anvin" <hpa@...or.com>,
Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 1/3] x86: KVM: VMX: Wrap GUEST_IA32_DEBUGCTL read/write with access functions
Instead of reading and writing GUEST_IA32_DEBUGCTL vmcs field directly,
wrap the logic with get/set functions.
Also move the checks that the guest's supplied value is valid to the new
'set' function.
In particular, the above change fixes a minor security issue in which L1
hypervisor could set the GUEST_IA32_DEBUGCTL, and eventually the host's
MSR_IA32_DEBUGCTL to any value by performing a VM entry to L2 with
VM_ENTRY_LOAD_DEBUG_CONTROLS set.
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
arch/x86/kvm/vmx/nested.c | 15 +++++++---
arch/x86/kvm/vmx/pmu_intel.c | 9 +++---
arch/x86/kvm/vmx/vmx.c | 58 +++++++++++++++++++++++-------------
arch/x86/kvm/vmx/vmx.h | 3 ++
4 files changed, 57 insertions(+), 28 deletions(-)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index e073e3008b16..b7686569ee09 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2641,6 +2641,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
struct vcpu_vmx *vmx = to_vmx(vcpu);
struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx);
bool load_guest_pdptrs_vmcs12 = false;
+ u64 new_debugctl;
if (vmx->nested.dirty_vmcs12 || nested_vmx_is_evmptr12_valid(vmx)) {
prepare_vmcs02_rare(vmx, vmcs12);
@@ -2653,11 +2654,17 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
if (vmx->nested.nested_run_pending &&
(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) {
kvm_set_dr(vcpu, 7, vmcs12->guest_dr7);
- vmcs_write64(GUEST_IA32_DEBUGCTL, vmcs12->guest_ia32_debugctl);
+ new_debugctl = vmcs12->guest_ia32_debugctl;
} else {
kvm_set_dr(vcpu, 7, vcpu->arch.dr7);
- vmcs_write64(GUEST_IA32_DEBUGCTL, vmx->nested.pre_vmenter_debugctl);
+ new_debugctl = vmx->nested.pre_vmenter_debugctl;
}
+
+ if (CC(!vmx_set_guest_debugctl(vcpu, new_debugctl, false))) {
+ *entry_failure_code = ENTRY_FAIL_DEFAULT;
+ return -EINVAL;
+ }
+
if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||
!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
vmcs_write64(GUEST_BNDCFGS, vmx->nested.pre_vmenter_bndcfgs);
@@ -3520,7 +3527,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
if (!vmx->nested.nested_run_pending ||
!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
- vmx->nested.pre_vmenter_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);
+ vmx->nested.pre_vmenter_debugctl = vmx_get_guest_debugctl(vcpu);
if (kvm_mpx_supported() &&
(!vmx->nested.nested_run_pending ||
!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
@@ -4788,7 +4795,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
__vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR);
kvm_set_dr(vcpu, 7, 0x400);
- vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
+ vmx_set_guest_debugctl(vcpu, 0, false);
if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr,
vmcs12->vm_exit_msr_load_count))
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 8a94b52c5731..f6f448adfb80 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -19,6 +19,7 @@
#include "lapic.h"
#include "nested.h"
#include "pmu.h"
+#include "vmx.h"
#include "tdx.h"
/*
@@ -652,11 +653,11 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu)
*/
static void intel_pmu_legacy_freezing_lbrs_on_pmi(struct kvm_vcpu *vcpu)
{
- u64 data = vmcs_read64(GUEST_IA32_DEBUGCTL);
+ u64 data = vmx_get_guest_debugctl(vcpu);
if (data & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI) {
data &= ~DEBUGCTLMSR_LBR;
- vmcs_write64(GUEST_IA32_DEBUGCTL, data);
+ vmx_set_guest_debugctl(vcpu, data, true);
}
}
@@ -729,7 +730,7 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu)
if (!lbr_desc->event) {
vmx_disable_lbr_msrs_passthrough(vcpu);
- if (vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR)
+ if (vmx_get_guest_debugctl(vcpu) & DEBUGCTLMSR_LBR)
goto warn;
if (test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use))
goto warn;
@@ -751,7 +752,7 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu)
static void intel_pmu_cleanup(struct kvm_vcpu *vcpu)
{
- if (!(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR))
+ if (!(vmx_get_guest_debugctl(vcpu) & DEBUGCTLMSR_LBR))
intel_pmu_release_guest_lbr_event(vcpu);
}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ef2d7208dd20..4237422dc4ed 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2154,7 +2154,7 @@ int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
break;
case MSR_IA32_DEBUGCTLMSR:
- msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
+ msr_info->data = vmx_get_guest_debugctl(vcpu);
break;
default:
find_uret_msr:
@@ -2194,6 +2194,41 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
return debugctl;
}
+u64 vmx_get_guest_debugctl(struct kvm_vcpu *vcpu)
+{
+ return vmcs_read64(GUEST_IA32_DEBUGCTL);
+}
+
+static void __vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 data)
+{
+ vmcs_write64(GUEST_IA32_DEBUGCTL, data);
+}
+
+bool vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 data, bool host_initiated)
+{
+ u64 invalid = data & ~vmx_get_supported_debugctl(vcpu, host_initiated);
+
+ if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
+ kvm_pr_unimpl_wrmsr(vcpu, MSR_IA32_DEBUGCTLMSR, data);
+ data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
+ invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
+ }
+
+ if (invalid)
+ return false;
+
+ if (is_guest_mode(vcpu) && (get_vmcs12(vcpu)->vm_exit_controls &
+ VM_EXIT_SAVE_DEBUG_CONTROLS))
+ get_vmcs12(vcpu)->guest_ia32_debugctl = data;
+
+ if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event &&
+ (data & DEBUGCTLMSR_LBR))
+ intel_pmu_create_guest_lbr_event(vcpu);
+
+ __vmx_set_guest_debugctl(vcpu, data);
+ return true;
+}
+
/*
* Writes msr value into the appropriate "register".
* Returns 0 on success, non-0 otherwise.
@@ -2263,26 +2298,9 @@ int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vmcs_writel(GUEST_SYSENTER_ESP, data);
break;
case MSR_IA32_DEBUGCTLMSR: {
- u64 invalid;
-
- invalid = data & ~vmx_get_supported_debugctl(vcpu, msr_info->host_initiated);
- if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
- kvm_pr_unimpl_wrmsr(vcpu, msr_index, data);
- data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
- invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
- }
-
- if (invalid)
+ if (!vmx_set_guest_debugctl(vcpu, data, msr_info->host_initiated))
return 1;
- if (is_guest_mode(vcpu) && get_vmcs12(vcpu)->vm_exit_controls &
- VM_EXIT_SAVE_DEBUG_CONTROLS)
- get_vmcs12(vcpu)->guest_ia32_debugctl = data;
-
- vmcs_write64(GUEST_IA32_DEBUGCTL, data);
- if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event &&
- (data & DEBUGCTLMSR_LBR))
- intel_pmu_create_guest_lbr_event(vcpu);
return 0;
}
case MSR_IA32_BNDCFGS:
@@ -4795,7 +4813,7 @@ static void init_vmcs(struct vcpu_vmx *vmx)
vmcs_write32(GUEST_SYSENTER_CS, 0);
vmcs_writel(GUEST_SYSENTER_ESP, 0);
vmcs_writel(GUEST_SYSENTER_EIP, 0);
- vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
+ __vmx_set_guest_debugctl(&vmx->vcpu, 0);
if (cpu_has_vmx_tpr_shadow()) {
vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, 0);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 6d1e40ecc024..8ac46fb47abd 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -404,6 +404,9 @@ u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
gva_t vmx_get_untagged_addr(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags);
+bool vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 value, bool host_initiated);
+u64 vmx_get_guest_debugctl(struct kvm_vcpu *vcpu);
+
static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
int type, bool value)
{
--
2.26.3
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