From 48e59373398a554098863bc7a3d1350cd0d5c4d0 Mon Sep 17 00:00:00 2001 From: David Matlack Date: Wed, 2 Nov 2022 11:46:46 -0700 Subject: [PATCH] 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 Reviewed-by: Sean Christopherson Link: https://lore.kernel.org/r/20221102184654.282799-3-dmatlack@google.com Signed-off-by: Sean Christopherson --- .../kvm/x86_64/smaller_maxphyaddr_emulation_test.c | 68 +++++++--------------- 1 file changed, 20 insertions(+), 48 deletions(-) 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 6fe5af8..6f7891b0 100644 --- 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, ®s); - regs.rip += 2; - vcpu_regs_set(vcpu, ®s); - } - } + 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, ®s); + regs.rip += 2; + vcpu_regs_set(vcpu, ®s); } static void do_guest_assert(struct ucall *uc) -- 2.7.4