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KVM: x86: Add a helper to handle filtering of unpermitted XCR0 features

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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>
This commit is contained in:
Aaron Lewis 2023-04-04 17:45:15 -07:00 committed by Sean Christopherson
parent 7712145073
commit 6be3ae45f5
3 changed files with 15 additions and 4 deletions
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2
arch/x86/kvm/cpuid.c
View File

@ -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;

4
arch/x86/kvm/x86.c
View File

@ -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;

13
arch/x86/kvm/x86.h
View File

@ -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))