executor: sys/linux: SYZOS: add AMD VMLOAD and VMSAVE primitives

This patch introduces SYZOS_API_NESTED_AMD_VMLOAD and
SYZOS_API_NESTED_AMD_VMSAVE.

These primitives allow the L1 guest to execute the VMLOAD and VMSAVE
instructions, which load/store additional guest state (FS, GS, TR, LDTR,
etc.) to/from the VMCB specified by the 'vm_id' argument.

This stresses the KVM L0 instruction emulator, which must validate the
L1-provided physical address in RAX and perform the state transfer.

Author: ramosian-glider

executor/common_kvm_amd64_syzos.h

@@ -38,6 +38,8 @@ typedef enum {
 	SYZOS_API_NESTED_AMD_CLGI = 383,
 	SYZOS_API_NESTED_AMD_INJECT_EVENT = 384,
 	SYZOS_API_NESTED_AMD_SET_INTERCEPT = 385,
+	SYZOS_API_NESTED_AMD_VMLOAD = 386,
+	SYZOS_API_NESTED_AMD_VMSAVE = 387,
 	SYZOS_API_STOP, // Must be the last one
 } syzos_api_id;
 
@@ -123,6 +125,8 @@ GUEST_CODE static void guest_handle_nested_amd_stgi();
 GUEST_CODE static void guest_handle_nested_amd_clgi();
 GUEST_CODE static void guest_handle_nested_amd_inject_event(struct api_call_5* cmd, uint64 cpu_id);
 GUEST_CODE static void guest_handle_nested_amd_set_intercept(struct api_call_5* cmd, uint64 cpu_id);
+GUEST_CODE static void guest_handle_nested_amd_vmload(struct api_call_1* cmd, uint64 cpu_id);
+GUEST_CODE static void guest_handle_nested_amd_vmsave(struct api_call_1* cmd, uint64 cpu_id);
 
 typedef enum {
 	UEXIT_END = (uint64)-1,
@@ -253,6 +257,12 @@ guest_main(uint64 size, uint64 cpu)
 		} else if (call == SYZOS_API_NESTED_AMD_SET_INTERCEPT) {
 			// Set/Clear specific intercept bits in the VMCB.
 			guest_handle_nested_amd_set_intercept((struct api_call_5*)cmd, cpu);
+		} else if (call == SYZOS_API_NESTED_AMD_VMLOAD) {
+			// Execute VMLOAD to load state from VMCB.
+			guest_handle_nested_amd_vmload((struct api_call_1*)cmd, cpu);
+		} else if (call == SYZOS_API_NESTED_AMD_VMSAVE) {
+			// Execute VMSAVE to save state to VMCB.
+			guest_handle_nested_amd_vmsave((struct api_call_1*)cmd, cpu);
 		}
 		addr += cmd->size;
 		size -= cmd->size;
@@ -1392,4 +1402,26 @@ guest_handle_nested_amd_set_intercept(struct api_call_5* cmd, uint64 cpu_id)
 	vmcb_write32(vmcb_addr, (uint16)offset, current);
 }
 
+GUEST_CODE static noinline void
+guest_handle_nested_amd_vmload(struct api_call_1* cmd, uint64 cpu_id)
+{
+	if (get_cpu_vendor() != CPU_VENDOR_AMD)
+		return;
+	uint64 vm_id = cmd->arg;
+	uint64 vmcb_pa = X86_SYZOS_ADDR_VMCS_VMCB(cpu_id, vm_id);
+
+	asm volatile("vmload %%rax" ::"a"(vmcb_pa) : "memory");
+}
+
+GUEST_CODE static noinline void
+guest_handle_nested_amd_vmsave(struct api_call_1* cmd, uint64 cpu_id)
+{
+	if (get_cpu_vendor() != CPU_VENDOR_AMD)
+		return;
+	uint64 vm_id = cmd->arg;
+	uint64 vmcb_pa = X86_SYZOS_ADDR_VMCS_VMCB(cpu_id, vm_id);
+
+	asm volatile("vmsave %%rax" ::"a"(vmcb_pa) : "memory");
+}
+
 #endif // EXECUTOR_COMMON_KVM_AMD64_SYZOS_H

sys/linux/dev_kvm_amd64.txt

@@ -191,6 +191,8 @@ syzos_api_call$x86 [
 	nested_amd_clgi			syzos_api$x86[383, void]
 	nested_amd_inject_event		syzos_api$x86[384, syzos_api_nested_amd_inject_event]
 	nested_amd_set_intercept	syzos_api$x86[385, syzos_api_nested_amd_set_intercept]
+	nested_amd_vmload		syzos_api$x86[386, syzos_api_vm_id]
+	nested_amd_vmsave		syzos_api$x86[387, syzos_api_vm_id]
 ] [varlen]
 
 kvm_text_x86 [

sys/linux/test/amd64-syz_kvm_nested_vmload_vmsave

@@ -0,0 +1,11 @@
+#
+# requires: arch=amd64 -threaded
+#
+
+# VMLOAD/VMSAVE Reproducer
+#
+r0 = openat$kvm(0xffffffffffffff9c, &AUTO='/dev/kvm\x00', 0x0, 0x0)
+r1 = ioctl$KVM_CREATE_VM(r0, 0x0, 0x0)
+r2 = syz_kvm_setup_syzos_vm$x86(r1, &(0x7f0000000000/0x400000)=nil)
+r3 = syz_kvm_add_vcpu$x86(r2, &AUTO={0x0, &AUTO=[@enable_nested={0x12c, 0x18, 0x0}, @nested_create_vm={0x12d, 0x18, 0x1}, @nested_amd_vmsave={0x183, 0x18, 0x1}, @nested_amd_vmload={0x182, 0x18, 0x1}], 0x0})
+ioctl$KVM_RUN(r3, 0x0, 0x0)