1 files changed, 95 insertions, 0 deletions
diff --git a/arch/um/kernel/skas/stub_exe.c b/arch/um/kernel/skas/stub_exe.c
new file mode 100644
index 000000000000..23c99b285e82
--- /dev/null
+++ b/arch/um/kernel/skas/stub_exe.c
@@ -0,0 +1,95 @@
+#include <sys/ptrace.h>
+#include <sys/prctl.h>
+#include <asm/unistd.h>
+#include <sysdep/stub.h>
+#include <stub-data.h>
+
+void _start(void);
+
+noinline static void real_init(void)
+{
+	struct stub_init_data init_data;
+	unsigned long res;
+	struct {
+		void  *ss_sp;
+		int    ss_flags;
+		size_t ss_size;
+	} stack = {
+		.ss_size = STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,
+	};
+	struct {
+		void *sa_handler_;
+		unsigned long sa_flags;
+		void *sa_restorer;
+		unsigned long long sa_mask;
+	} sa = {
+		/* Need to set SA_RESTORER (but the handler never returns) */
+		.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO | 0x04000000,
+		/* no need to mask any signals */
+		.sa_mask = 0,
+	};
+
+	/* set a nice name */
+	stub_syscall2(__NR_prctl, PR_SET_NAME, (unsigned long)"uml-userspace");
+
+	/* Make sure this process dies if the kernel dies */
+	stub_syscall2(__NR_prctl, PR_SET_PDEATHSIG, SIGKILL);
+
+	/* read information from STDIN and close it */
+	res = stub_syscall3(__NR_read, 0,
+			    (unsigned long)&init_data, sizeof(init_data));
+	if (res != sizeof(init_data))
+		stub_syscall1(__NR_exit, 10);
+
+	stub_syscall1(__NR_close, 0);
+
+	/* map stub code + data */
+	res = stub_syscall6(STUB_MMAP_NR,
+			    init_data.stub_start, UM_KERN_PAGE_SIZE,
+			    PROT_READ | PROT_EXEC, MAP_FIXED | MAP_SHARED,
+			    init_data.stub_code_fd, init_data.stub_code_offset);
+	if (res != init_data.stub_start)
+		stub_syscall1(__NR_exit, 11);
+
+	res = stub_syscall6(STUB_MMAP_NR,
+			    init_data.stub_start + UM_KERN_PAGE_SIZE,
+			    STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,
+			    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED,
+			    init_data.stub_data_fd, init_data.stub_data_offset);
+	if (res != init_data.stub_start + UM_KERN_PAGE_SIZE)
+		stub_syscall1(__NR_exit, 12);
+
+	/* setup signal stack inside stub data */
+	stack.ss_sp = (void *)init_data.stub_start + UM_KERN_PAGE_SIZE;
+	stub_syscall2(__NR_sigaltstack, (unsigned long)&stack, 0);
+
+	/* register SIGSEGV handler */
+	sa.sa_handler_ = (void *) init_data.segv_handler;
+	res = stub_syscall4(__NR_rt_sigaction, SIGSEGV, (unsigned long)&sa, 0,
+			    sizeof(sa.sa_mask));
+	if (res != 0)
+		stub_syscall1(__NR_exit, 13);
+
+	stub_syscall4(__NR_ptrace, PTRACE_TRACEME, 0, 0, 0);
+
+	stub_syscall2(__NR_kill, stub_syscall0(__NR_getpid), SIGSTOP);
+
+	stub_syscall1(__NR_exit, 14);
+
+	__builtin_unreachable();
+}
+
+__attribute__((naked)) void _start(void)
+{
+	/*
+	 * Since the stack after exec() starts at the top-most address,
+	 * but that's exactly where we also want to map the stub data
+	 * and code, this must:
+	 *  - push the stack by 1 code and STUB_DATA_PAGES data pages
+	 *  - call real_init()
+	 * This way, real_init() can use the stack normally, while the
+	 * original stack further down (higher address) will become
+	 * inaccessible after the mmap() calls above.
+	 */
+	stub_start(real_init);
+}