On Fri, May 05, 2023 at 05:20:42PM +0200, Mickaël Salaün wrote: > This enables guests to lock their CR0 and CR4 registers with a subset of > X86_CR0_WP, X86_CR4_SMEP, X86_CR4_SMAP, X86_CR4_UMIP, X86_CR4_FSGSBASE > and X86_CR4_CET flags. > > The new KVM_HC_LOCK_CR_UPDATE hypercall takes two arguments. The first > is to identify the control register, and the second is a bit mask to > pin (i.e. mark as read-only). > > These register flags should already be pinned by Linux guests, but once > compromised, this self-protection mechanism could be disabled, which is > not the case with this dedicated hypercall. > > Cc: Borislav Petkov <bp@xxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > Cc: H. Peter Anvin <hpa@xxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Sean Christopherson <seanjc@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx> > Link: https://lore.kernel.org/r/20230505152046.6575-6-mic@xxxxxxxxxxx [...] > hw_cr4 = (cr4_read_shadow() & X86_CR4_MCE) | (cr4 & ~X86_CR4_MCE); > if (is_unrestricted_guest(vcpu)) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ffab64d08de3..a529455359ac 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7927,11 +7927,77 @@ static unsigned long emulator_get_cr(struct x86_emulate_ctxt *ctxt, int cr) > return value; > } > > +#ifdef CONFIG_HEKI > + > +extern unsigned long cr4_pinned_mask; > + Can this be moved to a header file? > +static int heki_lock_cr(struct kvm *const kvm, const unsigned long cr, > + unsigned long pin) > +{ > + if (!pin) > + return -KVM_EINVAL; > + > + switch (cr) { > + case 0: > + /* Cf. arch/x86/kernel/cpu/common.c */ > + if (!(pin & X86_CR0_WP)) > + return -KVM_EINVAL; > + > + if ((read_cr0() & pin) != pin) > + return -KVM_EINVAL; > + > + atomic_long_or(pin, &kvm->heki_pinned_cr0); > + return 0; > + case 4: > + /* Checks for irrelevant bits. */ > + if ((pin & cr4_pinned_mask) != pin) > + return -KVM_EINVAL; > + It is enforcing the host mask on the guest, right? If the guest's set is a super set of the host's then it will get rejected. > + /* Ignores bits not present in host. */ > + pin &= __read_cr4(); > + atomic_long_or(pin, &kvm->heki_pinned_cr4); > + return 0; > + } > + return -KVM_EINVAL; > +} > + > +int heki_check_cr(const struct kvm *const kvm, const unsigned long cr, > + const unsigned long val) > +{ > + unsigned long pinned; > + > + switch (cr) { > + case 0: > + pinned = atomic_long_read(&kvm->heki_pinned_cr0); > + if ((val & pinned) != pinned) { > + pr_warn_ratelimited( > + "heki-kvm: Blocked CR0 update: 0x%lx\n", val); I think if the message contains the VM and VCPU identifier it will become more useful. Thanks, Wei.
