On 5/18/2024 1:38 AM, Sean Christopherson wrote:
Reject KVM_CAP_X86_DISABLE_EXITS if userspace attempts to disable MWAIT or
HLT exits and KVM previously reported (via KVM_CHECK_EXTENSION) that
disabling the exit(s) is not allowed. E.g. because MWAIT isn't supported
or the CPU doesn't have an aways-running APIC timer, or because KVM is
aways-running -> always-running
configured to mitigate cross-thread vulnerabilities.
Cc: Kechen Lu <kechenl@xxxxxxxxxx>
Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
Fixes: 6f0f2d5ef895 ("KVM: x86: Mitigate the cross-thread return address predictions bug")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 54 ++++++++++++++++++++++++----------------------
1 file changed, 28 insertions(+), 26 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4cb0c150a2f8..c729227c6501 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4590,6 +4590,20 @@ static inline bool kvm_can_mwait_in_guest(void)
boot_cpu_has(X86_FEATURE_ARAT);
}
+static u64 kvm_get_allowed_disable_exits(void)
+{
+ u64 r = KVM_X86_DISABLE_EXITS_PAUSE;
+
+ if (!mitigate_smt_rsb) {
+ r |= KVM_X86_DISABLE_EXITS_HLT |
+ KVM_X86_DISABLE_EXITS_CSTATE;
+
+ if (kvm_can_mwait_in_guest())
+ r |= KVM_X86_DISABLE_EXITS_MWAIT;
+ }
+ return r;
+}
+
#ifdef CONFIG_KVM_HYPERV
static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
struct kvm_cpuid2 __user *cpuid_arg)
@@ -4726,15 +4740,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = KVM_CLOCK_VALID_FLAGS;
break;
case KVM_CAP_X86_DISABLE_EXITS:
- r = KVM_X86_DISABLE_EXITS_PAUSE;
-
- if (!mitigate_smt_rsb) {
- r |= KVM_X86_DISABLE_EXITS_HLT |
- KVM_X86_DISABLE_EXITS_CSTATE;
-
- if (kvm_can_mwait_in_guest())
- r |= KVM_X86_DISABLE_EXITS_MWAIT;
- }
+ r |= kvm_get_allowed_disable_exits();
Nit: Just use "=".
break;
case KVM_CAP_X86_SMM:
if (!IS_ENABLED(CONFIG_KVM_SMM))
@@ -6565,33 +6571,29 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
break;
case KVM_CAP_X86_DISABLE_EXITS:
r = -EINVAL;
- if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
+ if (cap->args[0] & ~kvm_get_allowed_disable_exits())
break;
mutex_lock(&kvm->lock);
if (kvm->created_vcpus)
goto disable_exits_unlock;
- if (cap->args[0] & KVM_X86_DISABLE_EXITS_PAUSE)
- kvm->arch.pause_in_guest = true;
-
#define SMT_RSB_MSG "This processor is affected by the Cross-Thread Return Predictions vulnerability. " \
"KVM_CAP_X86_DISABLE_EXITS should only be used with SMT disabled or trusted guests."
- if (!mitigate_smt_rsb) {
- if (boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible() &&
- (cap->args[0] & ~KVM_X86_DISABLE_EXITS_PAUSE))
- pr_warn_once(SMT_RSB_MSG);
-
- if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
- kvm_can_mwait_in_guest())
- kvm->arch.mwait_in_guest = true;
- if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
- kvm->arch.hlt_in_guest = true;
- if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
- kvm->arch.cstate_in_guest = true;
- }
+ if (!mitigate_smt_rsb && boot_cpu_has_bug(X86_BUG_SMT_RSB) &&
+ cpu_smt_possible() &&
+ (cap->args[0] & ~KVM_X86_DISABLE_EXITS_PAUSE))
+ pr_warn_once(SMT_RSB_MSG);
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_PAUSE)
+ kvm->arch.pause_in_guest = true;
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT)
+ kvm->arch.mwait_in_guest = true;
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
+ kvm->arch.hlt_in_guest = true;
+ if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
+ kvm->arch.cstate_in_guest = true;
r = 0;
disable_exits_unlock:
mutex_unlock(&kvm->lock);
