[PATCH v4 04/21] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID
From: Yang Zhong <hidden>
Date: 2021-12-29 13:13:42
Also in:
kvm, linux-kselftest, lkml
Subsystem:
documentation, kernel virtual machine (kvm), kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Jonathan Corbet, Paolo Bonzini, Sean Christopherson, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
From: Jing Liu <redacted> KVM_GET_SUPPORTED_CPUID should not include any dynamic xstates in CPUID[0xD] if they have not been requested with prctl. Otherwise a process which directly passes KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2 would now fail even if it doesn't intend to use a dynamically enabled feature. Userspace must know that prctl is required and allocate >4K xstate buffer before setting any dynamic bit. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Jing Liu <redacted> Signed-off-by: Yang Zhong <redacted> --- Documentation/virt/kvm/api.rst | 4 ++++ arch/x86/kvm/cpuid.c | 9 ++++++--- 2 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index aeeb071c7688..1cf2483246cd 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst@@ -1684,6 +1684,10 @@ userspace capabilities, and with user requirements (for example, the user may wish to constrain cpuid to emulate older hardware, or for feature consistency across a cluster). +Dynamically-enabled feature bits need to be requested with +``arch_prctl()`` before calling this ioctl. Feature bits that have not +been requested are excluded from the result. + Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may expose cpuid features (e.g. MONITOR) which are not supported by kvm in its default configuration. If userspace enables such capabilities, it
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 148003e26cbb..4855344091b8 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c@@ -812,11 +812,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) goto out; } break; - case 0xd: - entry->eax &= supported_xcr0; + case 0xd: { + u64 guest_perm = xstate_get_guest_group_perm(); + + entry->eax &= supported_xcr0 & guest_perm; entry->ebx = xstate_required_size(supported_xcr0, false); entry->ecx = entry->ebx; - entry->edx &= supported_xcr0 >> 32; + entry->edx &= (supported_xcr0 & guest_perm) >> 32; if (!supported_xcr0) break;
@@ -863,6 +865,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) entry->edx = 0; } break; + } case 0x12: /* Intel SGX */ if (!kvm_cpu_cap_has(X86_FEATURE_SGX)) {