This is a note to let you know that I've just added the patch titled
KVM: VMX: Make CR0.WP a guest owned bit
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-vmx-make-cr0.wp-a-guest-owned-bit.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8ccf5dc3b7f7615c04f975bb8025d13949b5a436
Author: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Date: Mon May 8 17:46:01 2023 +0200
KVM: VMX: Make CR0.WP a guest owned bit
[ Upstream commit fb509f76acc8d42bed11bca308404f81c2be856a ]
Guests like grsecurity that make heavy use of CR0.WP to implement kernel
level W^X will suffer from the implied VMEXITs.
With EPT there is no need to intercept a guest change of CR0.WP, so
simply make it a guest owned bit if we can do so.
This implies that a read of a guest's CR0.WP bit might need a VMREAD.
However, the only potentially affected user seems to be kvm_init_mmu()
which is a heavy operation to begin with. But also most callers already
cache the full value of CR0 anyway, so no additional VMREAD is needed.
The only exception is nested_vmx_load_cr3().
This change is VMX-specific, as SVM has no such fine grained control
register intercept control.
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230322013731.102955-7-minipli@xxxxxxxxxxxxxx
Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx> # backport to v6.1.x
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index 3febc342360cc..896cc73949442 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -4,7 +4,7 @@
#include <linux/kvm_host.h>
-#define KVM_POSSIBLE_CR0_GUEST_BITS X86_CR0_TS
+#define KVM_POSSIBLE_CR0_GUEST_BITS (X86_CR0_TS | X86_CR0_WP)
#define KVM_POSSIBLE_CR4_GUEST_BITS \
(X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR \
| X86_CR4_OSXMMEXCPT | X86_CR4_PGE | X86_CR4_TSD | X86_CR4_FSGSBASE)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 8e56ec6e72e9d..9d683b6067c7b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4460,7 +4460,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
* CR0_GUEST_HOST_MASK is already set in the original vmcs01
* (KVM doesn't change it);
*/
- vcpu->arch.cr0_guest_owned_bits = KVM_POSSIBLE_CR0_GUEST_BITS;
+ vcpu->arch.cr0_guest_owned_bits = vmx_l1_guest_owned_cr0_bits();
vmx_set_cr0(vcpu, vmcs12->host_cr0);
/* Same as above - no reason to call set_cr4_guest_host_mask(). */
@@ -4611,7 +4611,7 @@ static void nested_vmx_restore_host_state(struct kvm_vcpu *vcpu)
*/
vmx_set_efer(vcpu, nested_vmx_get_vmcs01_guest_efer(vmx));
- vcpu->arch.cr0_guest_owned_bits = KVM_POSSIBLE_CR0_GUEST_BITS;
+ vcpu->arch.cr0_guest_owned_bits = vmx_l1_guest_owned_cr0_bits();
vmx_set_cr0(vcpu, vmcs_readl(CR0_READ_SHADOW));
vcpu->arch.cr4_guest_owned_bits = ~vmcs_readl(CR4_GUEST_HOST_MASK);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4984357c5d441..07aab85922441 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4695,7 +4695,7 @@ static void init_vmcs(struct vcpu_vmx *vmx)
/* 22.2.1, 20.8.1 */
vm_entry_controls_set(vmx, vmx_vmentry_ctrl());
- vmx->vcpu.arch.cr0_guest_owned_bits = KVM_POSSIBLE_CR0_GUEST_BITS;
+ vmx->vcpu.arch.cr0_guest_owned_bits = vmx_l1_guest_owned_cr0_bits();
vmcs_writel(CR0_GUEST_HOST_MASK, ~vmx->vcpu.arch.cr0_guest_owned_bits);
set_cr4_guest_host_mask(vmx);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index a3da84f4ea456..e2b04f4c0fef3 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -640,6 +640,24 @@ BUILD_CONTROLS_SHADOW(tertiary_exec, TERTIARY_VM_EXEC_CONTROL, 64)
(1 << VCPU_EXREG_EXIT_INFO_1) | \
(1 << VCPU_EXREG_EXIT_INFO_2))
+static inline unsigned long vmx_l1_guest_owned_cr0_bits(void)
+{
+ unsigned long bits = KVM_POSSIBLE_CR0_GUEST_BITS;
+
+ /*
+ * CR0.WP needs to be intercepted when KVM is shadowing legacy paging
+ * in order to construct shadow PTEs with the correct protections.
+ * Note! CR0.WP technically can be passed through to the guest if
+ * paging is disabled, but checking CR0.PG would generate a cyclical
+ * dependency of sorts due to forcing the caller to ensure CR0 holds
+ * the correct value prior to determining which CR0 bits can be owned
+ * by L1. Keep it simple and limit the optimization to EPT.
+ */
+ if (!enable_ept)
+ bits &= ~X86_CR0_WP;
+ return bits;
+}
+
static inline struct kvm_vmx *to_kvm_vmx(struct kvm *kvm)
{
return container_of(kvm, struct kvm_vmx, kvm);
