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KVM: x86: Filter out XTILE_CFG if XTILE_DATA isn't permitted 

Filter out XTILE_CFG from the supported XCR0 reported to userspace if the
current process doesn't have access to XTILE_DATA.  Attempting to set
XTILE_CFG in XCR0 will #GP if XTILE_DATA is also not set, and so keeping
XTILE_CFG as supported results in explosions if userspace feeds
KVM_GET_SUPPORTED_CPUID back into KVM and the guest doesn't sanity check
CPUID.

Fixes: 445ecdf79b ("kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID")
Reported-by: Aaron Lewis <aaronlewis@google.com>
Reviewed-by: Aaron Lewis <aaronlewis@google.com>
Tested-by: Aaron Lewis <aaronlewis@google.com>
Link: https://lore.kernel.org/r/20230405004520.421768-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-04-04 17:45:16 -07:00
parent 6be3ae45f5
commit 55cd57b596
1 changed files with 17 additions and 1 deletions
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18
arch/x86/kvm/x86.h
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@ -3,6 +3,7 @@
#define ARCH_X86_KVM_X86_H
#include <linux/kvm_host.h>
#include <asm/fpu/xstate.h>
#include <asm/mce.h>
#include <asm/pvclock.h>
#include "kvm_cache_regs.h"
@ -325,7 +326,22 @@ extern bool enable_pmu;
*/
static inline u64 kvm_get_filtered_xcr0(void)
{
return kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
u64 permitted_xcr0 = kvm_caps.supported_xcr0;
BUILD_BUG_ON(XFEATURE_MASK_USER_DYNAMIC != XFEATURE_MASK_XTILE_DATA);
if (permitted_xcr0 & XFEATURE_MASK_USER_DYNAMIC) {
permitted_xcr0 &= xstate_get_guest_group_perm();
/*
* Treat XTILE_CFG as unsupported if the current process isn't
* allowed to use XTILE_DATA, as attempting to set XTILE_CFG in
* XCR0 without setting XTILE_DATA is architecturally illegal.
*/
if (!(permitted_xcr0 & XFEATURE_MASK_XTILE_DATA))
permitted_xcr0 &= ~XFEATURE_MASK_XTILE_CFG;
}
return permitted_xcr0;
}
static inline bool kvm_mpx_supported(void)