executor: sys/linux: implement SYZOS_API_NESTED_VMRESUME

Provide the SYZOS API command to resume L2 execution after a VM exit,
using VMRESUME on Intel and VMRUN on AMD.

For testing purpose, implement basic handling of the INVD instruction:
 - enable INVD interception on AMD (set all bits in VMCB 00Ch);
 - map EXIT_REASON_INVD and VMEXIT_INVD into SYZOS_NESTED_EXIT_REASON_INVD;
 - advance L2 RIP to skip to the next instruction.

While at it, perform minor refactorings of L2 exit reason handling.

sys/linux/test/amd64-syz_kvm_nested_vmresume tests the new command by
executing two instructions, INVD and HLT, in the nested VM.

Author: ramosian-glider

executor/common_kvm_amd64_syzos.h

@@ -30,6 +30,7 @@ typedef enum {
 	SYZOS_API_NESTED_CREATE_VM = 301,
 	SYZOS_API_NESTED_LOAD_CODE = 302,
 	SYZOS_API_NESTED_VMLAUNCH = 303,
+	SYZOS_API_NESTED_VMRESUME = 304,
 	SYZOS_API_STOP, // Must be the last one
 } syzos_api_id;
 
@@ -102,6 +103,7 @@ GUEST_CODE static void guest_handle_enable_nested(struct api_call_1* cmd, uint64
 GUEST_CODE static void guest_handle_nested_create_vm(struct api_call_1* cmd, uint64 cpu_id);
 GUEST_CODE static void guest_handle_nested_load_code(struct api_call_nested_load_code* cmd, uint64 cpu_id);
 GUEST_CODE static void guest_handle_nested_vmlaunch(struct api_call_1* cmd, uint64 cpu_id);
+GUEST_CODE static void guest_handle_nested_vmresume(struct api_call_1* cmd, uint64 cpu_id);
 
 typedef enum {
 	UEXIT_END = (uint64)-1,
@@ -208,6 +210,9 @@ guest_main(uint64 size, uint64 cpu)
 		} else if (call == SYZOS_API_NESTED_VMLAUNCH) {
 			// Launch the nested VM.
 			guest_handle_nested_vmlaunch((struct api_call_1*)cmd, cpu);
+		} else if (call == SYZOS_API_NESTED_VMRESUME) {
+			// Resume a nested VM.
+			guest_handle_nested_vmresume((struct api_call_1*)cmd, cpu);
 		}
 		addr += cmd->size;
 		size -= cmd->size;
@@ -733,6 +738,7 @@ GUEST_CODE static noinline void init_vmcs_control_fields(uint64 cpu_id, uint64 v
 // Common L2 exit reasons for Intel and AMD.
 typedef enum {
 	SYZOS_NESTED_EXIT_REASON_HLT = 1,
+	SYZOS_NESTED_EXIT_REASON_INVD = 2,
 	SYZOS_NESTED_EXIT_REASON_UNKNOWN = 0xFF,
 } syz_nested_exit_reason;
 
@@ -748,22 +754,37 @@ GUEST_CODE static void guest_uexit_l2(uint64 exit_reason, syz_nested_exit_reason
 	}
 }
 
-GUEST_CODE static syz_nested_exit_reason map_intel_exit_reason(uint64 reason)
+#define EXIT_REASON_HLT 0xc
+#define EXIT_REASON_INVD 0xd
+
+GUEST_CODE static syz_nested_exit_reason map_intel_exit_reason(uint64 basic_reason)
 {
-	volatile uint64 basic_reason = reason & 0xFFFF;
-	// EXIT_REASON_HLT.
-	if (basic_reason == 0xc)
+	// Disable optimizations.
+	volatile uint64 reason = basic_reason;
+	if (reason == EXIT_REASON_HLT)
 		return SYZOS_NESTED_EXIT_REASON_HLT;
+	if (reason == EXIT_REASON_INVD)
+		return SYZOS_NESTED_EXIT_REASON_INVD;
 	return SYZOS_NESTED_EXIT_REASON_UNKNOWN;
 }
 
+GUEST_CODE static void advance_l2_rip_intel(uint64 basic_reason)
+{
+	if (basic_reason == EXIT_REASON_INVD) {
+		uint64 rip = vmread(VMCS_GUEST_RIP);
+		vmwrite(VMCS_GUEST_RIP, rip + 2);
+	}
+}
+
 // This function is called from inline assembly.
 __attribute__((used))
 GUEST_CODE static void
 nested_vm_exit_handler_intel(uint64 exit_reason, struct l2_guest_regs* regs)
 {
-	syz_nested_exit_reason mapped_reason = map_intel_exit_reason(exit_reason);
+	uint64 basic_reason = exit_reason & 0xFFFF;
+	syz_nested_exit_reason mapped_reason = map_intel_exit_reason(basic_reason);
 	guest_uexit_l2(exit_reason, mapped_reason, CPU_VENDOR_INTEL);
+	advance_l2_rip_intel(basic_reason);
 }
 
 extern char after_vmentry_label;
@@ -810,20 +831,36 @@ __attribute__((naked)) GUEST_CODE static void nested_vm_exit_handler_intel_asm(v
 			 [vm_exit_reason] "i"(VMCS_VM_EXIT_REASON) : "memory", "cc", "rbx", "rdi", "rsi");
 }
 
-GUEST_CODE static syz_nested_exit_reason map_amd_exit_reason(uint64 reason)
+#define VMEXIT_INVD 0x76
+#define VMEXIT_HLT 0x78
+
+GUEST_CODE static syz_nested_exit_reason map_amd_exit_reason(uint64 basic_reason)
 {
-	volatile uint64 basic_reason = reason & 0xFFFF;
-	// #VMEXIT_HLT.
-	if (basic_reason == 0x78)
+	// Disable optimizations.
+	volatile uint64 reason = basic_reason;
+	if (reason == VMEXIT_HLT)
 		return SYZOS_NESTED_EXIT_REASON_HLT;
+	if (reason == VMEXIT_INVD)
+		return SYZOS_NESTED_EXIT_REASON_INVD;
 	return SYZOS_NESTED_EXIT_REASON_UNKNOWN;
 }
 
+GUEST_CODE static void advance_l2_rip_amd(uint64 basic_reason, uint64 cpu_id, uint64 vm_id)
+{
+	if (basic_reason == VMEXIT_INVD) {
+		uint64 vmcb_addr = X86_SYZOS_ADDR_VMCS_VMCB(cpu_id, vm_id);
+		uint64 rip = vmcb_read64((volatile uint8*)vmcb_addr, VMCB_GUEST_RIP);
+		vmcb_write64(vmcb_addr, VMCB_GUEST_RIP, rip + 2);
+	}
+}
+
 __attribute__((used)) GUEST_CODE static void
 nested_vm_exit_handler_amd(uint64 exit_reason, uint64 cpu_id, uint64 vm_id)
 {
-	syz_nested_exit_reason mapped_reason = map_amd_exit_reason(exit_reason);
+	volatile uint64 basic_reason = exit_reason & 0xFFFF;
+	syz_nested_exit_reason mapped_reason = map_amd_exit_reason(basic_reason);
 	guest_uexit_l2(exit_reason, mapped_reason, CPU_VENDOR_AMD);
+	advance_l2_rip_amd(basic_reason, cpu_id, vm_id);
 }
 
 GUEST_CODE static noinline void init_vmcs_host_state(void)
@@ -1011,7 +1048,7 @@ GUEST_CODE static noinline void init_vmcb_guest_state(uint64 cpu_id, uint64 vm_i
 	vmcb_write32(vmcb_addr, VMCB_GUEST_IDTR_LIM, idtr.limit);
 
 	// Setup VMCB Control Fields.
-	vmcb_write32(vmcb_addr, VMCB_CTRL_INTERCEPT_VEC3, VMCB_CTRL_INTERCEPT_HLT);
+	vmcb_write32(vmcb_addr, VMCB_CTRL_INTERCEPT_VEC3, VMCB_CTRL_INTERCEPT_VEC3_ALL);
 	vmcb_write32(vmcb_addr, VMCB_CTRL_INTERCEPT_VEC4, VMCB_CTRL_INTERCEPT_VEC4_ALL);
 
 	// Enable Nested Paging (NPT):
@@ -1078,9 +1115,8 @@ guest_handle_nested_load_code(struct api_call_nested_load_code* cmd, uint64 cpu_
 }
 
 GUEST_CODE static noinline void
-guest_handle_nested_vmentry_intel(struct api_call_1* cmd, uint64 cpu_id, bool is_launch)
+guest_handle_nested_vmentry_intel(uint64 vm_id, uint64 cpu_id, bool is_launch)
 {
-	uint64 vm_id = cmd->arg;
 	uint64 vmx_error_code = 0;
 	uint8 fail_flag = 0; // Will be 1 if EITHER CF or ZF is set
 
@@ -1149,19 +1185,24 @@ guest_run_amd_vm(uint64 cpu_id, uint64 vm_id)
 }
 
 GUEST_CODE static noinline void
-guest_handle_nested_vmlaunch_amd(struct api_call_1* cmd, uint64 cpu_id, uint64 vm_id)
+guest_handle_nested_vmlaunch(struct api_call_1* cmd, uint64 cpu_id)
 {
-	guest_run_amd_vm(cpu_id, vm_id);
+	uint64 vm_id = cmd->arg;
+	if (get_cpu_vendor() == CPU_VENDOR_INTEL) {
+		guest_handle_nested_vmentry_intel(vm_id, cpu_id, true);
+	} else {
+		guest_run_amd_vm(cpu_id, vm_id);
+	}
 }
 
 GUEST_CODE static noinline void
-guest_handle_nested_vmlaunch(struct api_call_1* cmd, uint64 cpu_id)
+guest_handle_nested_vmresume(struct api_call_1* cmd, uint64 cpu_id)
 {
 	uint64 vm_id = cmd->arg;
 	if (get_cpu_vendor() == CPU_VENDOR_INTEL) {
-		guest_handle_nested_vmentry_intel(cmd, cpu_id, true);
+		guest_handle_nested_vmentry_intel(vm_id, cpu_id, false);
 	} else {
-		guest_handle_nested_vmlaunch_amd(cmd, cpu_id, vm_id);
+		guest_run_amd_vm(cpu_id, vm_id);
 	}
 }
 

executor/kvm.h

@@ -393,7 +393,7 @@
 
 // Control Area
 #define VMCB_CTRL_INTERCEPT_VEC3 0x0c
-#define VMCB_CTRL_INTERCEPT_HLT (1 << 24) // Bit 24 in VEC3
+#define VMCB_CTRL_INTERCEPT_VEC3_ALL (0xffffffff)
 #define VMCB_CTRL_INTERCEPT_VEC4 0x10
 // Bits 0-9: intercept VMRUN, VMMCALL, VMLOAD, VMSAVE, STGI, CLGI, SKINIT, RDTSCP, ICEBP, WBINVD.
 #define VMCB_CTRL_INTERCEPT_VEC4_ALL (0x3ff)

sys/linux/dev_kvm_amd64.txt

@@ -117,6 +117,7 @@ syzos_api_call$x86 [
 	nested_create_vm	syzos_api$x86[301, syzos_api_vm_id]
 	nested_load_code	syzos_api$x86[302, syzos_api_nested_load_code]
 	nested_vmlaunch		syzos_api$x86[303, syzos_api_vm_id]
+	nested_vmresume		syzos_api$x86[304, syzos_api_vm_id]
 ] [varlen]
 
 kvm_text_x86 [

sys/linux/test/amd64-syz_kvm_nested_vmresume

@@ -0,0 +1,29 @@
+#
+# 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$x86(r1, &(0x7f0000c00000/0x400000)=nil)
+
+# Create a nested VM that performs INVD (0f 08) and HLT (f4) to test vmresume.
+# INVD is one of the few instructions that cause unconditional VM exit on Intel.
+# On AMD, SYZOS also turns on INVD interception.
+#
+r3 = syz_kvm_add_vcpu$x86(r2, &AUTO={0x0, &AUTO=[@enable_nested={AUTO, AUTO, 0x0}, @nested_create_vm={AUTO, AUTO, 0x0}, @nested_load_code={AUTO, AUTO, {0x0, "0f08f4"}}, @nested_vmlaunch={AUTO, AUTO, 0x0}, @nested_vmresume={AUTO, AUTO, 0x0}], AUTO})
+r4 = ioctl$KVM_GET_VCPU_MMAP_SIZE(r0, AUTO)
+r5 = mmap$KVM_VCPU(&(0x7f0000009000/0x1000)=nil, r4, 0x3, 0x1, r3, 0x0)
+
+# L2 VM executes INVD. Exit reason is mapped to 0xe2e20002.
+#
+ioctl$KVM_RUN(r3, AUTO, 0x0)
+syz_kvm_assert_syzos_uexit$x86(r5, 0xe2e20002)
+
+# L1 resumes L2, which executes HLT. Exit reason is mapped to 0xe2e20001.
+#
+ioctl$KVM_RUN(r3, AUTO, 0x0)
+syz_kvm_assert_syzos_uexit$x86(r5, 0xe2e20001)
+
+# guest_main should finish with guest_uexit(-1).
+#
+ioctl$KVM_RUN(r3, AUTO, 0x0)
+syz_kvm_assert_syzos_uexit$x86(r5, 0xffffffff)