Re: [PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check

From: Binbin Wu
Date: Tue Apr 25 2023 - 21:47:04 EST

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In reply to: Zeng Guang: "Re: [PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check"
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On 4/25/2023 11:26 AM, Zeng Guang wrote:

On 4/24/2023 3:43 PM, Binbin Wu wrote:

[...]

On 4/20/2023 9:37 PM, Zeng Guang wrote:

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index abccd51dcfca..f76c07f2674b 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -131,6 +131,7 @@ 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(check_lass);
      #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 8ff89a52ef66..31fb8699a1ff 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -69,6 +69,9 @@
   #define KVM_X86_NOTIFY_VMEXIT_VALID_BITS (KVM_X86_NOTIFY_VMEXIT_ENABLED | \
                            KVM_X86_NOTIFY_VMEXIT_USER)
   +/* x86-specific emulation flags */
+#define KVM_X86_EMULFLAG_SKIP_LASS    _BITULL(1)
Do you use the flag outside of emulator?
For LAM patch, it's planned to move the flags inside emulator.

IMO, the detailed flag is implementation specific. Is it necessary to bind with emulator
though it's only used inside emulator ?

For the rest part (i.e., VMExit handlings), the code is already in the vendor specific implementations.
The callers are aware of the information to skip LASS check or not.

I plan to do a cleanup to consolidate the flags into one parameter for __linearize().
And the consolidated flags value will be extended for LAM and other features (e.g. LASS).

I post the proposed patch as following, could you help to check wether it is OK for LASS to follow?

arch/x86/kvm/emulate.c     | 20 ++++++++++++++------
arch/x86/kvm/kvm_emulate.h | 4 ++++
2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a20bec931764..5fb516bc5731 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -687,8 +687,8 @@ static unsigned insn_alignment(struct x86_emulate_ctxt *ctxt, unsigned size)
static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
                        struct segmented_address addr,
                        unsigned *max_size, unsigned size,
-                       bool write, bool fetch,
-                       enum x86emul_mode mode, ulong *linear)
+                       u64 flags, enum x86emul_mode mode,
+                       ulong *linear)
{
     struct desc_struct desc;
     bool usable;
@@ -696,6 +696,8 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
     u32 lim;
     u16 sel;
     u8 va_bits;
+    bool fetch = !!(flags & X86_EMULFLAG_FETCH);
+    bool write = !!(flags & X86_EMULFLAG_WRITE);

     la = seg_base(ctxt, addr.seg) + addr.ea;
     *max_size = 0;
@@ -757,7 +759,12 @@ static int linearize(struct x86_emulate_ctxt *ctxt,
              ulong *linear)
{
     unsigned max_size;
-    return __linearize(ctxt, addr, &max_size, size, write, false,
+    u64 flags = 0;
+
+    if (write)
+        flags |= X86_EMULFLAG_WRITE;
+
+    return __linearize(ctxt, addr, &max_size, size, flags,
                ctxt->mode, linear);
}

@@ -768,10 +775,11 @@ static inline int assign_eip(struct x86_emulate_ctxt *ctxt, ulong dst)
     unsigned max_size;
     struct segmented_address addr = { .seg = VCPU_SREG_CS,
                        .ea = dst };
+    u64 flags = X86_EMULFLAG_FETCH;

     if (ctxt->op_bytes != sizeof(unsigned long))
         addr.ea = dst & ((1UL << (ctxt->op_bytes << 3)) - 1);
-    rc = __linearize(ctxt, addr, &max_size, 1, false, true, ctxt->mode, &linear);
+    rc = __linearize(ctxt, addr, &max_size, 1, flags, ctxt->mode, &linear);
     if (rc == X86EMUL_CONTINUE)
         ctxt->_eip = addr.ea;
     return rc;
@@ -896,6 +904,7 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
     int cur_size = ctxt->fetch.end - ctxt->fetch.data;
     struct segmented_address addr = { .seg = VCPU_SREG_CS,
                        .ea = ctxt->eip + cur_size };
+    u64 flags = X86_EMULFLAG_FETCH;

     /*
     * We do not know exactly how many bytes will be needed, and
@@ -907,8 +916,7 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
     * boundary check itself. Instead, we use max_size to check
     * against op_size.
     */
-    rc = __linearize(ctxt, addr, &max_size, 0, false, true, ctxt->mode,
-            &linear);
+    rc = __linearize(ctxt, addr, &max_size, 0, flags, ctxt->mode, &linear);
     if (unlikely(rc != X86EMUL_CONTINUE))
         return rc;

diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index ab65f3a47dfd..5451a37f135f 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -88,6 +88,10 @@ struct x86_instruction_info {
#define X86EMUL_IO_NEEDED       5 /* IO is needed to complete emulation */
#define X86EMUL_INTERCEPTED     6 /* Intercepted by nested VMCB/VMCS */

+/* x86-specific emulation flags */
+#define X86_EMULFLAG_FETCH            _BITULL(0)
+#define X86_EMULFLAG_WRITE            _BITULL(1)
+
struct x86_emulate_ops {
     void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);
     /*

+
   /* x86-specific vcpu->requests bit members */
   #define KVM_REQ_MIGRATE_TIMER        KVM_ARCH_REQ(0)
   #define KVM_REQ_REPORT_TPR_ACCESS    KVM_ARCH_REQ(1)
@@ -1706,6 +1709,8 @@ struct kvm_x86_ops {
        * Returns vCPU specific APICv inhibit reasons
        */
       unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
+
+    bool (*check_lass)(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags);
The flags may be dropped if the caller knows to skip it or not.

Probably I don't get you right. Do you mean it need define another function without flags ?

   };
      struct kvm_x86_nested_ops {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c923d7599d71..581327ede66a 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8070,6 +8070,59 @@ static void vmx_vm_destroy(struct kvm *kvm)
       free_pages((unsigned long)kvm_vmx->pid_table, vmx_get_pid_table_order(kvm));
   }
   +/*
+ * Determine whether an access to the linear address causes a LASS violation.
+ * LASS protection is only effective in long mode. As a prerequisite, caller
+ * should make sure VM

Should be vCPU？

Similar meaning, I think. :)

running in long mode and invoke this api to do LASS
+ * violation check.
+ */
+bool __vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags)
+{
+    bool user_mode, user_as, rflags_ac;
+
+    if (!!(flags & KVM_X86_EMULFLAG_SKIP_LASS) ||
+        !kvm_is_cr4_bit_set(vcpu, X86_CR4_LASS))
+        return false;
+
+    WARN_ON_ONCE(!is_long_mode(vcpu));
+
+    user_as = !(la >> 63);
+
+    /*
+     * An access is a supervisor-mode access if CPL < 3 or if it implicitly
+     * accesses a system data structure. For implicit accesses to system
+     * data structure, the processor acts as if RFLAGS.AC is clear.
+     */
+    if (access & PFERR_IMPLICIT_ACCESS) {
+        user_mode = false;
+        rflags_ac = false;
+    } else {
+        user_mode = vmx_get_cpl(vcpu) == 3;
+        if (!user_mode)
+            rflags_ac = !!(kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+    }
+
+    if (user_mode != user_as) {
+        /*
+         * Supervisor-mode _data_ accesses to user address space
+         * cause LASS violations only if SMAP is enabled.
+         */
+        if (!user_mode && !(access & PFERR_FETCH_MASK)) {
+            return kvm_is_cr4_bit_set(vcpu, X86_CR4_SMAP) &&
+                   !rflags_ac;
+        } else {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+static bool vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags)
+{
+    return is_long_mode(vcpu) && __vmx_check_lass(vcpu, access, la, flags);
+}
+
   static struct kvm_x86_ops vmx_x86_ops __initdata = {
       .name = "kvm_intel",
   @@ -8207,6 +8260,8 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
       .complete_emulated_msr = kvm_complete_insn_gp,
          .vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
+
+    .check_lass = vmx_check_lass,
   };
      static unsigned int vmx_handle_intel_pt_intr(void)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index a3da84f4ea45..6569385a5978 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -433,6 +433,8 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
   u64 vmx_get_l2_tsc_offset(struct kvm_vcpu *vcpu);
   u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
   +bool __vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags);
+
   static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
                            int type, bool value)
   {

Next message: Justin Forbes: "Re: [PATCH 6.2 000/110] 6.2.13-rc1 review"
Previous message: kernel test robot: "Re: [PATCH 33/34] maple_tree: Add testing for mas_{prev,next}_range()"
In reply to: Zeng Guang: "Re: [PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check"
Next in thread: Chao Gao: "Re: [PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check"
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