executor/kvm: add SYZOS support for CPUID

This commit adds support for CPUID instructions on AMD64. It also adds a
relevant test.

Author: marpom

executor/common_kvm_amd64_syzos.h

@@ -21,6 +21,7 @@ extern char *__start_guest, *__stop_guest;
 typedef enum {
 	SYZOS_API_UEXIT,
 	SYZOS_API_CODE,
+	SYZOS_API_CPUID,
 	SYZOS_API_STOP, // Must be the last one
 } syzos_api_id;
 
@@ -39,8 +40,15 @@ struct api_call_code {
 	uint8 insns[];
 };
 
+struct api_call_cpuid {
+	struct api_call_header header;
+	uint32 eax;
+	uint32 ecx;
+};
+
 static void guest_uexit(uint64 exit_code);
 static void guest_execute_code(uint8* insns, uint64 size);
+static void guest_cpuid(uint32 eax, uint32 ecx);
 
 typedef enum {
 	UEXIT_END = (uint64)-1,
@@ -73,6 +81,10 @@ guest_main(uint64 size, uint64 cpu)
 			guest_execute_code(ccmd->insns, cmd->size - sizeof(struct api_call_header));
 			break;
 		}
+		case SYZOS_API_CPUID: {
+			struct api_call_cpuid* ccmd = (struct api_call_cpuid*)cmd;
+			guest_cpuid(ccmd->eax, ccmd->ecx);
+		}
 		}
 		addr += cmd->size;
 		size -= cmd->size;
@@ -94,3 +106,12 @@ GUEST_CODE static noinline void guest_uexit(uint64 exit_code)
 	volatile uint64* ptr = (volatile uint64*)X86_ADDR_UEXIT;
 	*ptr = exit_code;
 }
+
+GUEST_CODE static noinline void guest_cpuid(uint32 eax, uint32 ecx)
+{
+	asm volatile(
+	    "cpuid\n"
+	    : // Currently ignore outputs
+	    : "a"(eax), "c"(ecx)
+	    : "rbx", "rdx");
+}

sys/linux/dev_kvm_amd64.txt

@@ -43,9 +43,15 @@ type syzos_api$x86[NUM, PAYLOAD] {
 	payload	PAYLOAD
 }
 
+syzos_api_cpuid {
+	eax	int32
+	ecx	int32
+}
+
 syzos_api_call$x86 [
 	uexit	syzos_api$x86[0, intptr]
 	code	syzos_api$x86[1, syzos_api_code$x86]
+	cpuid	syzos_api$x86[2, syzos_api_cpuid]
 ] [varlen]
 
 kvm_text_x86 [

sys/linux/test/amd64-syz_kvm_setup_syzos_vm-cpuid

@@ -0,0 +1,17 @@
+#
+# requires: arch=amd64 -threaded
+#
+r0 = openat$kvm(0, &AUTO='/dev/kvm\x00', 0x0, 0x0)
+r1 = ioctl$KVM_CREATE_VM(r0, AUTO, 0x0)
+r2 = syz_kvm_setup_syzos_vm$x86(r1, &(0x7f0000c00000/0x400000)=nil)
+#
+# 0x2 queries Cache and TLB information
+#
+r3 = syz_kvm_add_vcpu$x86(r2, &AUTO={0x0, &AUTO=[@cpuid={AUTO, AUTO, {0x1, 0x0}}], AUTO})
+r4 = ioctl$KVM_GET_VCPU_MMAP_SIZE(r0, AUTO)
+r5 = mmap$KVM_VCPU(&(0x7f0000009000/0x1000)=nil, r4, 0x3, 0x1, r3, 0x0)
+
+# Run till the end of guest_main(). 0xffffffffffffffff is UEXIT_END.
+#
+ioctl$KVM_RUN(r3, AUTO, 0x0)
+syz_kvm_assert_syzos_uexit$x86(r5, 0xffffffffffffffff)