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KVM: x86: Mitigate the cross-thread return address predictions bug

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commit 6f0f2d5ef895d66a3f2b32dd05189ec34afa5a55 upstream.

By default, KVM/SVM will intercept attempts by the guest to transition
out of C0. However, the KVM_CAP_X86_DISABLE_EXITS capability can be used
by a VMM to change this behavior. To mitigate the cross-thread return
address predictions bug (X86_BUG_SMT_RSB), a VMM must not be allowed to
override the default behavior to intercept C0 transitions.

Use a module parameter to control the mitigation on processors that are
vulnerable to X86_BUG_SMT_RSB. If the processor is vulnerable to the
X86_BUG_SMT_RSB bug and the module parameter is set to mitigate the bug,
KVM will not allow the disabling of the HLT, MWAIT and CSTATE exits.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <4019348b5e07148eb4d593380a5f6713b93c9a16.1675956146.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tom Lendacky 2023-02-09 09:22:25 -06:00 committed by Greg Kroah-Hartman
parent 8f12dcab90
commit 5122e0e443
1 changed files with 32 additions and 11 deletions
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43
arch/x86/kvm/x86.c
View File

@ -184,6 +184,10 @@ module_param(force_emulation_prefix, bool, S_IRUGO);
int __read_mostly pi_inject_timer = -1;
module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
/* Enable/disable SMT_RSB bug mitigation */
bool __read_mostly mitigate_smt_rsb;
module_param(mitigate_smt_rsb, bool, 0444);
/*
* Restoring the host value for MSRs that are only consumed when running in
* usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
@ -4164,10 +4168,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = KVM_CLOCK_TSC_STABLE;
break;
case KVM_CAP_X86_DISABLE_EXITS:
r |= KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
KVM_X86_DISABLE_EXITS_CSTATE;
if(kvm_can_mwait_in_guest())
r |= KVM_X86_DISABLE_EXITS_MWAIT;
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;
}
break;
case KVM_CAP_X86_SMM:
/* SMBASE is usually relocated above 1M on modern chipsets,
@ -5746,15 +5755,26 @@ split_irqchip_unlock:
if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
break;
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_PAUSE)
kvm->arch.pause_in_guest = true;
if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
kvm->arch.cstate_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;
}
r = 0;
break;
case KVM_CAP_MSR_PLATFORM_INFO:
@ -12796,6 +12816,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_vmgexit_msr_protocol_exit);
static int __init kvm_x86_init(void)
{
kvm_mmu_x86_module_init();
mitigate_smt_rsb &= boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible();
return 0;
}
module_init(kvm_x86_init);