6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit 7cafe9b8e22bb3d77f130c461aedf6868c4aaf58 upstream.
Check for nested TSC scaling support on nested SVM VMRUN instead of
asserting that TSC scaling is exposed to L1 if L1's MSR_AMD64_TSC_RATIO
has diverged from KVM's default. Userspace can trigger the WARN at will
by writing the MSR and then updating guest CPUID to hide the feature
(modifying guest CPUID is allowed anytime before KVM_RUN). E.g. hacking
KVM's state_test selftest to do
vcpu_set_msr(vcpu, MSR_AMD64_TSC_RATIO, 0);
vcpu_clear_cpuid_feature(vcpu, X86_FEATURE_TSCRATEMSR);
after restoring state in a new VM+vCPU yields an endless supply of:
------------[ cut here ]------------
WARNING: CPU: 164 PID: 62565 at arch/x86/kvm/svm/nested.c:699
nested_vmcb02_prepare_control+0x3d6/0x3f0 [kvm_amd]
Call Trace:
<TASK>
enter_svm_guest_mode+0x114/0x560 [kvm_amd]
nested_svm_vmrun+0x260/0x330 [kvm_amd]
vmrun_interception+0x29/0x30 [kvm_amd]
svm_invoke_exit_handler+0x35/0x100 [kvm_amd]
svm_handle_exit+0xe7/0x180 [kvm_amd]
kvm_arch_vcpu_ioctl_run+0x1eab/0x2570 [kvm]
kvm_vcpu_ioctl+0x4c9/0x5b0 [kvm]
__se_sys_ioctl+0x7a/0xc0
__x64_sys_ioctl+0x21/0x30
do_syscall_64+0x41/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x45ca1b
Note, the nested #VMEXIT path has the same flaw, but needs a different
fix and will be handled separately.
Fixes: 5228eb96a487 ("KVM: x86: nSVM: implement nested TSC scaling")
Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230729011608.1065019-2-seanjc@xxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm/nested.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -695,10 +695,9 @@ static void nested_vmcb02_prepare_contro
vmcb02->control.tsc_offset = vcpu->arch.tsc_offset;
- if (svm->tsc_ratio_msr != kvm_caps.default_tsc_scaling_ratio) {
- WARN_ON(!svm->tsc_scaling_enabled);
+ if (svm->tsc_scaling_enabled &&
+ svm->tsc_ratio_msr != kvm_caps.default_tsc_scaling_ratio)
nested_svm_update_tsc_ratio_msr(vcpu);
- }
vmcb02->control.int_ctl =
(svm->nested.ctl.int_ctl & int_ctl_vmcb12_bits) |
