Re: [PATCH v2 5/8] KVM: emulator: Add emulation of LASS violation checks on linear address

[Chao Gao]

On Tue, Jul 18, 2023 at 09:18:41PM +0800, Zeng Guang wrote:
>When enabled Intel CPU feature Linear Address Space Separation (LASS),
>KVM emulator will take LASS violation check on every access to guest
>memory by a linear address.

When Intel Linear Address Space Separation (LASS) is enabled, the processor
applies a LASS violation check to every access to a linear address. To
align with hardware behavior, KVM needs to perform the same check in
instruction emulation.

>
>We defined a new function prototype in kvm_x86_ops for emulator to
>construct the interface to identify whether a LASS violation occurs.
>It can have further practical implementation according to vendor
>specific requirements.
>
>Emulator will use the passed (address, size) pair and instruction
>operation type (flags) to enforce LASS protection when KVM emulates
>instruction fetch, data access including implicit data access to a
>system data structure.

Define a new function in x86_emulator_ops to perform the LASS violation
check in KVM emulator. The function accepts an address and a size, which
delimit the memory access, and a flag, which provides extra information
about the access that is necessary for LASS violation checks, e.g., whether
the access is an instruction fetch or implicit access.

emulator_is_lass_violation() is just a placeholder. it will be wired up
to VMX/SVM implementation by a later patch.

(I think the commit message can also explain why the LASS violation
 check is added in the three functions, i.e., __linearize(),
 linear_read_system() and linear_write_system(), and why only in them)

>
>Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
>Tested-by: Xuelian Guo <xuelian.guo@xxxxxxxxx>
>---
> arch/x86/include/asm/kvm-x86-ops.h |  3 ++-
> arch/x86/include/asm/kvm_host.h    |  3 +++
> arch/x86/kvm/emulate.c             | 11 +++++++++++
> arch/x86/kvm/kvm_emulate.h         |  2 ++
> arch/x86/kvm/x86.c                 | 10 ++++++++++
> 5 files changed, 28 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
>index 13bc212cd4bc..a301f0a46381 100644
>--- a/arch/x86/include/asm/kvm-x86-ops.h
>+++ b/arch/x86/include/asm/kvm-x86-ops.h
>@@ -132,7 +132,8 @@ KVM_X86_OP_OPTIONAL(migrate_timers)
> KVM_X86_OP(msr_filter_changed)
> KVM_X86_OP(complete_emulated_msr)
> KVM_X86_OP(vcpu_deliver_sipi_vector)
>-KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
>+KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons)
>+KVM_X86_OP_OPTIONAL_RET0(is_lass_violation)

...

> 
> #undef KVM_X86_OP
> #undef KVM_X86_OP_OPTIONAL
>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>index fb9d1f2d6136..791f0dd48cd9 100644
>--- a/arch/x86/include/asm/kvm_host.h
>+++ b/arch/x86/include/asm/kvm_host.h
>@@ -1731,6 +1731,9 @@ struct kvm_x86_ops {
> 	 * Returns vCPU specific APICv inhibit reasons
> 	 */
> 	unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
>+
>+	bool (*is_lass_violation)(struct kvm_vcpu *vcpu, unsigned long addr,
>+				  unsigned int size, unsigned int flags);

I may think we can just return false in emulator_is_lass_violation() and
fold this new kvm_x86_ops definition into its vmx implementation. This way
is more natural to me.

> };
> 
> struct kvm_x86_nested_ops {
>diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>index 9b4b3ce6d52a..2289a4ad21be 100644
>--- a/arch/x86/kvm/emulate.c
>+++ b/arch/x86/kvm/emulate.c
>@@ -742,6 +742,10 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
> 		}
> 		break;
> 	}
>+
>+	if (ctxt->ops->is_lass_violation(ctxt, *linear, size, flags))
>+		goto bad;
>+
> 	if (la & (insn_alignment(ctxt, size) - 1))
> 		return emulate_gp(ctxt, 0);
> 	return X86EMUL_CONTINUE;
>@@ -848,6 +852,9 @@ static inline int jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
> static int linear_read_system(struct x86_emulate_ctxt *ctxt, ulong linear,
> 			      void *data, unsigned size)
> {
>+	if (ctxt->ops->is_lass_violation(ctxt, linear, size, X86EMUL_F_IMPLICIT))
>+		return emulate_gp(ctxt, 0);
>+
> 	return ctxt->ops->read_std(ctxt, linear, data, size, &ctxt->exception, true);
> }
> 
>@@ -855,6 +862,10 @@ static int linear_write_system(struct x86_emulate_ctxt *ctxt,
> 			       ulong linear, void *data,
> 			       unsigned int size)
> {
>+	if (ctxt->ops->is_lass_violation(ctxt, linear, size,
>+					 X86EMUL_F_IMPLICIT | X86EMUL_F_FETCH))

s/X86EMUL_F_FETCH/X86EMUL_F_WRITE/