The patch below does not apply to the 5.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 139f7425fdf54f054463e7524b9f54c41af8407f Mon Sep 17 00:00:00 2001

From: Paolo Bonzini pbonzini@redhat.com Date: Tue, 5 May 2020 09:40:46 -0400 Subject: [PATCH] kvm: x86: Use KVM CPU capabilities to determine CR4 reserved bits

Using CPUID data can be useful for the processor compatibility check, but that's it. Using it to compute guest-reserved bits can have both false positives (such as LA57 and UMIP which we are already handling) and false negatives: in particular, with this patch we don't allow anymore a KVM guest to set CR4.PKE when CR4.PKE is clear on the host.

Fixes: b9dd21e104bc ("KVM: x86: simplify handling of PKRU") Reported-by: Jim Mattson jmattson@google.com Tested-by: Jim Mattson jmattson@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c5835f9cb9ad..8d296e3d0d56 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -926,19 +926,6 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr); __reserved_bits; \ })

-static u64 kvm_host_cr4_reserved_bits(struct cpuinfo_x86 *c) -{ - u64 reserved_bits = __cr4_reserved_bits(cpu_has, c); - - if (kvm_cpu_cap_has(X86_FEATURE_LA57)) - reserved_bits &= ~X86_CR4_LA57; - - if (kvm_cpu_cap_has(X86_FEATURE_UMIP)) - reserved_bits &= ~X86_CR4_UMIP; - - return reserved_bits; -} - static int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4) { if (cr4 & cr4_reserved_bits) @@ -9675,7 +9662,9 @@ int kvm_arch_hardware_setup(void *opaque) if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES)) supported_xss = 0;

- cr4_reserved_bits = kvm_host_cr4_reserved_bits(&boot_cpu_data); +#define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f) + cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_); +#undef __kvm_cpu_cap_has

if (kvm_has_tsc_control) { /* @@ -9707,7 +9696,8 @@ int kvm_arch_check_processor_compat(void *opaque)

WARN_ON(!irqs_disabled());

- if (kvm_host_cr4_reserved_bits(c) != cr4_reserved_bits) + if (__cr4_reserved_bits(cpu_has, c) != + __cr4_reserved_bits(cpu_has, &boot_cpu_data)) return -EIO;

return ops->check_processor_compatibility();