From 394265079b6c271fdc191ac31b1ebfbee3dd6d63 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 28 Sep 2022 23:36:47 +0000 Subject: [PATCH] KVM: selftests: Compare insn opcodes directly in fix_hypercall_test MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Directly compare the expected versus observed hypercall instructions when verifying that KVM patched in the native hypercall (FIX_HYPERCALL_INSN quirk enabled). gcc rightly complains that doing a 4-byte memcpy() with an "unsigned char" as the source generates an out-of-bounds accesses. Alternatively, "exp" and "obs" could be declared as 3-byte arrays, but there's no known reason to copy locally instead of comparing directly. In function ‘assert_hypercall_insn’, inlined from ‘guest_main’ at x86_64/fix_hypercall_test.c:91:2: x86_64/fix_hypercall_test.c:63:9: error: array subscript ‘unsigned int[0]’ is partly outside array bounds of ‘unsigned char[1]’ [-Werror=array-bounds] 63 | memcpy(&exp, exp_insn, sizeof(exp)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ x86_64/fix_hypercall_test.c: In function ‘guest_main’: x86_64/fix_hypercall_test.c:42:22: note: object ‘vmx_hypercall_insn’ of size 1 42 | extern unsigned char vmx_hypercall_insn; | ^~~~~~~~~~~~~~~~~~ x86_64/fix_hypercall_test.c:25:22: note: object ‘svm_hypercall_insn’ of size 1 25 | extern unsigned char svm_hypercall_insn; | ^~~~~~~~~~~~~~~~~~ In function ‘assert_hypercall_insn’, inlined from ‘guest_main’ at x86_64/fix_hypercall_test.c:91:2: x86_64/fix_hypercall_test.c:64:9: error: array subscript ‘unsigned int[0]’ is partly outside array bounds of ‘unsigned char[1]’ [-Werror=array-bounds] 64 | memcpy(&obs, obs_insn, sizeof(obs)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ x86_64/fix_hypercall_test.c: In function ‘guest_main’: x86_64/fix_hypercall_test.c:25:22: note: object ‘svm_hypercall_insn’ of size 1 25 | extern unsigned char svm_hypercall_insn; | ^~~~~~~~~~~~~~~~~~ x86_64/fix_hypercall_test.c:42:22: note: object ‘vmx_hypercall_insn’ of size 1 42 | extern unsigned char vmx_hypercall_insn; | ^~~~~~~~~~~~~~~~~~ cc1: all warnings being treated as errors make: *** [../lib.mk:135: tools/testing/selftests/kvm/x86_64/fix_hypercall_test] Error 1 Fixes: 6c2fa8b20d0c ("selftests: KVM: Test KVM_X86_QUIRK_FIX_HYPERCALL_INSN") Cc: Oliver Upton Signed-off-by: Sean Christopherson Reviewed-by: Oliver Upton Message-Id: <20220928233652.783504-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- .../selftests/kvm/x86_64/fix_hypercall_test.c | 34 ++++++++++------------ 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c index b1905d2..e0004bd 100644 --- a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c +++ b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c @@ -14,6 +14,9 @@ #include "kvm_util.h" #include "processor.h" +/* VMCALL and VMMCALL are both 3-byte opcodes. */ +#define HYPERCALL_INSN_SIZE 3 + static bool ud_expected; static void guest_ud_handler(struct ex_regs *regs) @@ -22,7 +25,7 @@ static void guest_ud_handler(struct ex_regs *regs) GUEST_DONE(); } -extern unsigned char svm_hypercall_insn; +extern uint8_t svm_hypercall_insn[HYPERCALL_INSN_SIZE]; static uint64_t svm_do_sched_yield(uint8_t apic_id) { uint64_t ret; @@ -39,7 +42,7 @@ static uint64_t svm_do_sched_yield(uint8_t apic_id) return ret; } -extern unsigned char vmx_hypercall_insn; +extern uint8_t vmx_hypercall_insn[HYPERCALL_INSN_SIZE]; static uint64_t vmx_do_sched_yield(uint8_t apic_id) { uint64_t ret; @@ -56,30 +59,20 @@ static uint64_t vmx_do_sched_yield(uint8_t apic_id) return ret; } -static void assert_hypercall_insn(unsigned char *exp_insn, unsigned char *obs_insn) -{ - uint32_t exp = 0, obs = 0; - - memcpy(&exp, exp_insn, sizeof(exp)); - memcpy(&obs, obs_insn, sizeof(obs)); - - GUEST_ASSERT_EQ(exp, obs); -} - static void guest_main(void) { - unsigned char *native_hypercall_insn, *hypercall_insn; + uint8_t *native_hypercall_insn, *hypercall_insn; uint8_t apic_id; apic_id = GET_APIC_ID_FIELD(xapic_read_reg(APIC_ID)); if (is_intel_cpu()) { - native_hypercall_insn = &vmx_hypercall_insn; - hypercall_insn = &svm_hypercall_insn; + native_hypercall_insn = vmx_hypercall_insn; + hypercall_insn = svm_hypercall_insn; svm_do_sched_yield(apic_id); } else if (is_amd_cpu()) { - native_hypercall_insn = &svm_hypercall_insn; - hypercall_insn = &vmx_hypercall_insn; + native_hypercall_insn = svm_hypercall_insn; + hypercall_insn = vmx_hypercall_insn; vmx_do_sched_yield(apic_id); } else { GUEST_ASSERT(0); @@ -87,8 +80,13 @@ static void guest_main(void) return; } + /* + * The hypercall didn't #UD (guest_ud_handler() signals "done" if a #UD + * occurs). Verify that a #UD is NOT expected and that KVM patched in + * the native hypercall. + */ GUEST_ASSERT(!ud_expected); - assert_hypercall_insn(native_hypercall_insn, hypercall_insn); + GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn, HYPERCALL_INSN_SIZE)); GUEST_DONE(); } -- 2.7.4