KVM: selftests: Explicitly require instructions bytes

Hard-code the flds instruction and assert the exact instruction bytes
are present in run->emulation_failure. The test already requires the
instruction bytes to be present because that's the only way the test
will advance the RIP past the flds and get to GUEST_DONE().

Note that KVM does not necessarily return exactly 2 bytes in
run->emulation_failure since it may not know the exact instruction
length in all cases. So just assert that
run->emulation_failure.insn_size is at least 2.

Signed-off-by: David Matlack <dmatlack@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221102184654.282799-3-dmatlack@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c b/tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c
index 6fe5af8bd47eff9863d9d78e9c548eb611e4d9d0..6f7891b0e193b2476d7a4a2dab0f8c1546177e38 100644 (file)
--- a/tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c
+++ b/tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c
@@ -19,41 +19,20 @@
 #define MEM_REGION_SLOT        10
 #define MEM_REGION_SIZE PAGE_SIZE
 
+#define FLDS_MEM_EAX ".byte 0xd9, 0x00"
+
 static void guest_code(void)
 {
-       __asm__ __volatile__("flds (%[addr])"
-                            :: [addr]"r"(MEM_REGION_GVA));
+       __asm__ __volatile__(FLDS_MEM_EAX :: "a"(MEM_REGION_GVA));
 
        GUEST_DONE();
 }
 
-/*
- * Accessors to get R/M, REG, and Mod bits described in the SDM vol 2,
- * figure 2-2 "Table Interpretation of ModR/M Byte (C8H)".
- */
-#define GET_RM(insn_byte) (insn_byte & 0x7)
-#define GET_REG(insn_byte) ((insn_byte & 0x38) >> 3)
-#define GET_MOD(insn_byte) ((insn_byte & 0xc) >> 6)
-
-/* Ensure we are dealing with a simple 2-byte flds instruction. */
-static bool is_flds(uint8_t *insn_bytes, uint8_t insn_size)
-{
-       return insn_size >= 2 &&
-              insn_bytes[0] == 0xd9 &&
-              GET_REG(insn_bytes[1]) == 0x0 &&
-              GET_MOD(insn_bytes[1]) == 0x0 &&
-              /* Ensure there is no SIB byte. */
-              GET_RM(insn_bytes[1]) != 0x4 &&
-              /* Ensure there is no displacement byte. */
-              GET_RM(insn_bytes[1]) != 0x5;
-}
-
 static void process_exit_on_emulation_error(struct kvm_vcpu *vcpu)
 {
        struct kvm_run *run = vcpu->run;
        struct kvm_regs regs;
        uint8_t *insn_bytes;
-       uint8_t insn_size;
        uint64_t flags;
 
        TEST_ASSERT(run->exit_reason == KVM_EXIT_INTERNAL_ERROR,
@@ -65,30 +44,23 @@ static void process_exit_on_emulation_error(struct kvm_vcpu *vcpu)
                    "Unexpected suberror: %u",
                    run->emulation_failure.suberror);
 
-       if (run->emulation_failure.ndata >= 1) {
-               flags = run->emulation_failure.flags;
-               if ((flags & KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES) &&
-                   run->emulation_failure.ndata >= 3) {
-                       insn_size = run->emulation_failure.insn_size;
-                       insn_bytes = run->emulation_failure.insn_bytes;
-
-                       TEST_ASSERT(insn_size <= 15 && insn_size > 0,
-                                   "Unexpected instruction size: %u",
-                                   insn_size);
-
-                       TEST_ASSERT(is_flds(insn_bytes, insn_size),
-                                   "Unexpected instruction.  Expected 'flds' (0xd9 /0)");
-
-                       /*
-                        * If is_flds() succeeded then the instruction bytes
-                        * contained an flds instruction that is 2-bytes in
-                        * length (ie: no prefix, no SIB, no displacement).
-                        */
-                       vcpu_regs_get(vcpu, &regs);
-                       regs.rip += 2;
-                       vcpu_regs_set(vcpu, &regs);
-               }
-       }
+       flags = run->emulation_failure.flags;
+       TEST_ASSERT(run->emulation_failure.ndata >= 3 &&
+                   flags & KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES,
+                   "run->emulation_failure is missing instruction bytes");
+
+       TEST_ASSERT(run->emulation_failure.insn_size >= 2,
+                   "Expected a 2-byte opcode for 'flds', got %d bytes",
+                   run->emulation_failure.insn_size);
+
+       insn_bytes = run->emulation_failure.insn_bytes;
+       TEST_ASSERT(insn_bytes[0] == 0xd9 && insn_bytes[1] == 0,
+                   "Expected 'flds [eax]', opcode '0xd9 0x00', got opcode 0x%02x 0x%02x\n",
+                   insn_bytes[0], insn_bytes[1]);
+
+       vcpu_regs_get(vcpu, &regs);
+       regs.rip += 2;
+       vcpu_regs_set(vcpu, &regs);
 }
 
 static void do_guest_assert(struct ucall *uc)