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KVM: selftests: Explicitly require instructions bytes

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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>
This commit is contained in:
David Matlack 2022-11-02 11:46:46 -07:00 committed by Sean Christopherson
parent 52d3a4fb5b
commit 48e5937339
1 changed files with 17 additions and 45 deletions
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62
tools/testing/selftests/kvm/x86_64/smaller_maxphyaddr_emulation_test.c
View File

@ -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;
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(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);
}
}
vcpu_regs_get(vcpu, &regs);
regs.rip += 2;
vcpu_regs_set(vcpu, &regs);
}
static void do_guest_assert(struct ucall *uc)