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authorAaron Lewis <aaronlewis@google.com>2023-04-04 17:45:15 -0700
committerSean Christopherson <seanjc@google.com>2023-04-11 10:19:03 -0700
commit6be3ae45f567cdebb5b9938137bf3445ceacf9fb (patch)
tree84ecd4be65938442d421322bd51d8bc7c4be5dc2 /arch/x86/kvm
parent7712145073876092e9aa81f0b836fef8b5694b14 (diff)
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KVM: x86: Add a helper to handle filtering of unpermitted XCR0 features
Add a helper, kvm_get_filtered_xcr0(), to dedup code that needs to account for XCR0 features that require explicit opt-in on a per-process basis. In addition to documenting when KVM should/shouldn't consult xstate_get_guest_group_perm(), the helper will also allow sanitizing the filtered XCR0 to avoid enumerating architecturally illegal XCR0 values, e.g. XTILE_CFG without XTILE_DATA. No functional changes intended. Signed-off-by: Aaron Lewis <aaronlewis@google.com> Reviewed-by: Mingwei Zhang <mizhang@google.com> [sean: rename helper, move to x86.h, massage changelog] Reviewed-by: Aaron Lewis <aaronlewis@google.com> Tested-by: Aaron Lewis <aaronlewis@google.com> Link: https://lore.kernel.org/r/20230405004520.421768-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r--arch/x86/kvm/cpuid.c2
-rw-r--r--arch/x86/kvm/x86.c4
-rw-r--r--arch/x86/kvm/x86.h13
3 files changed, 15 insertions, 4 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9583a110cf5f..1daf0df6a9b8 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1002,7 +1002,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->eax = entry->ebx = entry->ecx = 0;
break;
case 0xd: {
- u64 permitted_xcr0 = kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
+ u64 permitted_xcr0 = kvm_get_filtered_xcr0();
u64 permitted_xss = kvm_caps.supported_xss;
entry->eax &= permitted_xcr0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 237c483b1230..181f155933cf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4531,9 +4531,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = 0;
break;
case KVM_CAP_XSAVE2: {
- u64 guest_perm = xstate_get_guest_group_perm();
-
- r = xstate_required_size(kvm_caps.supported_xcr0 & guest_perm, false);
+ r = xstate_required_size(kvm_get_filtered_xcr0(), false);
if (r < sizeof(struct kvm_xsave))
r = sizeof(struct kvm_xsave);
break;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index a8167b47b8c8..9589c86812eb 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -315,6 +315,19 @@ extern struct kvm_caps kvm_caps;
extern bool enable_pmu;
+/*
+ * Get a filtered version of KVM's supported XCR0 that strips out dynamic
+ * features for which the current process doesn't (yet) have permission to use.
+ * This is intended to be used only when enumerating support to userspace,
+ * e.g. in KVM_GET_SUPPORTED_CPUID and KVM_CAP_XSAVE2, it does NOT need to be
+ * used to check/restrict guest behavior as KVM rejects KVM_SET_CPUID{2} if
+ * userspace attempts to enable unpermitted features.
+ */
+static inline u64 kvm_get_filtered_xcr0(void)
+{
+ return kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
+}
+
static inline bool kvm_mpx_supported(void)
{
return (kvm_caps.supported_xcr0 & (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR))