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KVM: x86: Reject disabling of MWAIT/HLT interception when not allowed

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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 always-running APIC timer, or because KVM is
configured to mitigate cross-thread vulnerabilities.

Cc: Kechen Lu <kechenl@nvidia.com>
Fixes: 4d5422cea3 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
Fixes: 6f0f2d5ef8 ("KVM: x86: Mitigate the cross-thread return address predictions bug")
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20241128013424.4096668-15-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2024-11-27 17:33:41 -08:00
parent 04cd8f8628
commit c829ccd4d9
1 changed files with 28 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/x86/kvm/x86.c
+28 -26
View File
@@ -4531,6 +4531,20 @@ 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)
@@ -4673,15 +4687,7 @@ 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();
break;
case KVM_CAP_X86_SMM:
if (!IS_ENABLED(CONFIG_KVM_SMM))
@@ -6528,33 +6534,29 @@ split_irqchip_unlock:
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);