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@@ -108,7 +108,7 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
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wait_stub_done(pid);
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/*
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- * faultinfo is prepared by the stub-segv-handler at start of
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+ * faultinfo is prepared by the stub_segv_handler at start of
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* the stub stack page. We just have to copy it.
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*/
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memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
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@@ -175,6 +175,21 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,
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extern char __syscall_stub_start[];
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+/**
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+ * userspace_tramp() - userspace trampoline
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+ * @stack: pointer to the new userspace stack page, can be NULL, if? FIXME:
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+ *
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+ * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
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+ * This function will run on a temporary stack page.
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+ * It ptrace()'es itself, then
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+ * Two pages are mapped into the userspace address space:
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+ * - STUB_CODE (with EXEC), which contains the skas stub code
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+ * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
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+ * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
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+ * And last the process stops itself to give control to the UML kernel for this userspace process.
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+ *
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+ * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
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+ */
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static int userspace_tramp(void *stack)
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{
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void *addr;
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@@ -236,12 +251,24 @@ static int userspace_tramp(void *stack)
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int userspace_pid[NR_CPUS];
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+/**
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+ * start_userspace() - prepare a new userspace process
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+ * @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME:
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+ *
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+ * Setups a new temporary stack page that is used while userspace_tramp() runs
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+ * Clones the kernel process into a new userspace process, with FDs only.
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+ *
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+ * Return: When positive: the process id of the new userspace process,
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+ * when negative: an error number.
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+ * FIXME: can PIDs become negative?!
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+ */
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int start_userspace(unsigned long stub_stack)
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{
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void *stack;
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unsigned long sp;
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int pid, status, n, flags, err;
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+ /* setup a temporary stack page */
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stack = mmap(NULL, UM_KERN_PAGE_SIZE,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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@@ -252,10 +279,12 @@ int start_userspace(unsigned long stub_stack)
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return err;
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}
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+ /* set stack pointer to the end of the stack page, so it can grow downwards */
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sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
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flags = CLONE_FILES | SIGCHLD;
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+ /* clone into new userspace process */
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pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
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if (pid < 0) {
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err = -errno;
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@@ -323,11 +352,17 @@ void userspace(struct uml_pt_regs *regs)
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* fail. In this case, there is nothing to do but
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* just kill the process.
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*/
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- if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
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+ if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
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+ printk(UM_KERN_ERR "userspace - ptrace set regs "
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+ "failed, errno = %d\n", errno);
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fatal_sigsegv();
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+ }
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- if (put_fp_registers(pid, regs->fp))
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+ if (put_fp_registers(pid, regs->fp)) {
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+ printk(UM_KERN_ERR "userspace - ptrace set fp regs "
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+ "failed, errno = %d\n", errno);
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fatal_sigsegv();
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+ }
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/* Now we set local_using_sysemu to be used for one loop */
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local_using_sysemu = get_using_sysemu();
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