Commit 48e59373 authored by David Matlack's avatar David Matlack Committed by Sean Christopherson
Browse files

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: default avatarDavid Matlack <dmatlack@google.com>
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221102184654.282799-3-dmatlack@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 52d3a4fb

tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c

+20 −48
Original line number Diff line number Diff line
@@ -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,
@@ -65,31 +44,24 @@ 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(run->emulation_failure.ndata >= 3 &&

		    flags & KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES,

		    "run->emulation_failure is missing instruction bytes");



			TEST_ASSERT(insn_size <= 15 && insn_size > 0,

				    "Unexpected instruction size: %u",

				    insn_size);

	TEST_ASSERT(run->emulation_failure.insn_size >= 2,

		    "Expected a 2-byte opcode for 'flds', got %d bytes",

		    run->emulation_failure.insn_size);



			TEST_ASSERT(is_flds(insn_bytes, insn_size),

				    "Unexpected instruction.  Expected 'flds' (0xd9 /0)");

	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]);



			/*

			 * 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);

}

	}

}



static void do_guest_assert(struct ucall *uc)

{