[Xen-devel] [PATCH v2 3/3] x86/hvm: Corrections to RDTSCP intercept handling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

For both VT-x and SVM, the RDTSCP intercept will trigger if the pipeline
supports the instruction, but the guest may have not have rdtscp in its
featureset.  Bring the vmexit handlers in line with the main emulator
behaviour by optionally handing back #UD.

Next on the AMD side, if RDTSCP actually ends up being intercepted on a debug
build, we first update regs->rcx, then call __get_instruction_length() asking
for RDTSC.  As the two instructions are different (and indeed, different
lengths!), __get_instruction_length_from_list() fails and hands back a #GP
fault.

This can demonstrated by putting a guest into tsc_mode="always emulate" and
executing an rdtscp instruction:

  (d1) --- Xen Test Framework ---
  (d1) Environment: HVM 64bit (Long mode 4 levels)
  (d1) Test rdtscp
  (d1) TSC mode 1
  (XEN) emulate.c:147:d1v0 svm_get_insn_len: Mismatch between expected and 
actual instruction:
  (XEN) emulate.c:152:d1v0   insn_index 8, opcode 0xf0031 modrm 0
  (XEN) emulate.c:154:d1v0   rip 0x10475f, nextrip 0x104762, len 3
  (XEN) SVM insn len emulation failed (1): d1v0 64bit @ 0008:0010475f -> 0f 01 
f9 0f 31 5b 31 ff 31 c0 e9 c2 db ff ff 00
  (d1) ******************************
  (d1) PANIC: Unhandled exception at 0008:000000000010475f
  (d1) Vec 13 #GP[0000]
  (d1) ******************************

First, teach svm_get_insn_len() to cope with RDTSCP, and improve
svm_vmexit_do_rdtsc() to ask for the correct instruction.  Move the regs->rcx
adjustment into this function to ensure it gets done after we are done
potentially raising faults.

Reported-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Brian Woods <brian.woods@xxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>

v2:
 * Rebase
---
 xen/arch/x86/hvm/svm/emulate.c        |  1 +
 xen/arch/x86/hvm/svm/svm.c            | 22 +++++++++++++++++-----
 xen/arch/x86/hvm/vmx/vmx.c            |  8 ++++++++
 xen/include/asm-x86/hvm/svm/emulate.h |  1 +
 4 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/emulate.c b/xen/arch/x86/hvm/svm/emulate.c
index 73cef5b..0778dc7 100644
--- a/xen/arch/x86/hvm/svm/emulate.c
+++ b/xen/arch/x86/hvm/svm/emulate.c
@@ -75,6 +75,7 @@ static const struct {
     [INSTR_STGI]    = { X86EMUL_OPC(0x0f, 0x01), MODRM(3, 3, 4) },
     [INSTR_CLGI]    = { X86EMUL_OPC(0x0f, 0x01), MODRM(3, 3, 5) },
     [INSTR_INVLPGA] = { X86EMUL_OPC(0x0f, 0x01), MODRM(3, 3, 7) },
+    [INSTR_RDTSCP]  = { X86EMUL_OPC(0x0f, 0x01), MODRM(3, 7, 1) },
     [INSTR_INVD]    = { X86EMUL_OPC(0x0f, 0x08) },
     [INSTR_WBINVD]  = { X86EMUL_OPC(0x0f, 0x09) },
     [INSTR_WRMSR]   = { X86EMUL_OPC(0x0f, 0x30) },
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index f8b7e8b..d2c0d64 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2279,14 +2279,28 @@ static void svm_vmexit_do_hlt(struct vmcb_struct *vmcb,
     hvm_hlt(regs->eflags);
 }
 
-static void svm_vmexit_do_rdtsc(struct cpu_user_regs *regs)
+static void svm_vmexit_do_rdtsc(struct cpu_user_regs *regs, bool rdtscp)
 {
+    struct vcpu *curr = current;
+    const struct domain *currd = curr->domain;
+    enum instruction_index insn = rdtscp ? INSTR_RDTSCP : INSTR_RDTSC;
     unsigned int inst_len;
 
-    if ( (inst_len = svm_get_insn_len(current, INSTR_RDTSC)) == 0 )
+    if ( rdtscp && !currd->arch.cpuid->extd.rdtscp &&
+         currd->arch.tsc_mode != TSC_MODE_PVRDTSCP )
+    {
+        hvm_inject_hw_exception(TRAP_invalid_op, X86_EVENT_NO_EC);
         return;
+    }
+
+    if ( (inst_len = svm_get_insn_len(curr, insn)) == 0 )
+        return;
+
     __update_guest_eip(regs, inst_len);
 
+    if ( rdtscp )
+        regs->rcx = hvm_msr_tsc_aux(curr);
+
     hvm_rdtsc_intercept(regs);
 }
 
@@ -2966,10 +2980,8 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
         break;
 
     case VMEXIT_RDTSCP:
-        regs->rcx = hvm_msr_tsc_aux(v);
-        /* fall through */
     case VMEXIT_RDTSC:
-        svm_vmexit_do_rdtsc(regs);
+        svm_vmexit_do_rdtsc(regs, exit_reason == VMEXIT_RDTSCP);
         break;
 
     case VMEXIT_MONITOR:
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 7f77d1f..2166b0d 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3589,6 +3589,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     unsigned long exit_qualification, exit_reason, idtv_info, intr_info = 0;
     unsigned int vector = 0, mode;
     struct vcpu *v = current;
+    struct domain *currd = v->domain;
 
     __vmread(GUEST_RIP,    &regs->rip);
     __vmread(GUEST_RSP,    &regs->rsp);
@@ -3956,6 +3957,13 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         vmx_invlpg_intercept(exit_qualification);
         break;
     case EXIT_REASON_RDTSCP:
+        if ( !currd->arch.cpuid->extd.rdtscp &&
+             currd->arch.tsc_mode != TSC_MODE_PVRDTSCP )
+        {
+            hvm_inject_hw_exception(TRAP_invalid_op, X86_EVENT_NO_EC);
+            break;
+        }
+
         regs->rcx = hvm_msr_tsc_aux(v);
         /* fall through */
     case EXIT_REASON_RDTSC:
diff --git a/xen/include/asm-x86/hvm/svm/emulate.h 
b/xen/include/asm-x86/hvm/svm/emulate.h
index 1d062d2..1f7a075 100644
--- a/xen/include/asm-x86/hvm/svm/emulate.h
+++ b/xen/include/asm-x86/hvm/svm/emulate.h
@@ -30,6 +30,7 @@ enum instruction_index {
     INSTR_HLT,
     INSTR_INT3,
     INSTR_RDTSC,
+    INSTR_RDTSCP,
     INSTR_PAUSE,
     INSTR_XSETBV,
     INSTR_VMRUN,
-- 
2.1.4


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