Method valid_syscall

dependencies/vdm/vdm_ctx/vdm_ctx.cpp:94–118

	}

	bool vdm_ctx::valid_syscall(void* syscall_addr) const
	{
		static std::mutex syscall_mutex;
		syscall_mutex.lock();

		static const auto proc =
			GetProcAddress(
				LoadLibraryA(syscall_hook.second),
				syscall_hook.first
			);

		// 0:  48 31 c0    xor rax, rax
		// 3 : c3          ret
		std::uint8_t shellcode[] = { 0x48, 0x31, 0xC0, 0xC3 };
		std::uint8_t orig_bytes[sizeof shellcode];

		// save original bytes and install shellcode...
		read_phys(syscall_addr, orig_bytes, sizeof orig_bytes);
		write_phys(syscall_addr, shellcode, sizeof shellcode);

		auto result = reinterpret_cast<NTSTATUS(__fastcall*)(void)>(proc)();
		write_phys(syscall_addr, orig_bytes, sizeof orig_bytes);
		syscall_mutex.unlock();
		return result == STATUS_SUCCESS;
	}
}