uml: kill processes instead of panicing kernel

UML was panicing in the case of failures of libc calls which shouldn't happen.
 This is an overreaction since a failure from libc doesn't normally mean that
kernel data structures are in an unknown state.  Instead, the current process
should just be killed if there is no way to recover.

The case that prompted this was a failure of PTRACE_SETREGS restoring the same
state that was read by PTRACE_GETREGS.  It appears that when a process tries
to load a bogus value into a segment register, it segfaults (as expected) and
the value is actually loaded and is seen by PTRACE_GETREGS (not expected).

This case is fixed by forcing a fatal SIGSEGV on the process so that it
immediately dies.  fatal_sigsegv was added for this purpose.  It was declared
as noreturn, so in order to pursuade gcc that it actually does not return, I
added a call to os_dump_core (and declared it noreturn) so that I get a core
file if somehow the process survives.

All other calls in arch/um/os-Linux/skas/process.c got the same treatment,
with failures causing the process to die instead of a kernel panic, with some
exceptions.

userspace_tramp exits with status 1 if anything goes wrong there.  That will
cause start_userspace to return an error.  copy_context_skas0 and
map_stub_pages also now return errors instead of panicing.  Callers of thes
functions were changed to check for errors and do something appropriate.
Usually that's to return an error to their callers.
check_skas3_ptrace_faultinfo just exits since that's too early to do anything
else.

save_registers, restore_registers, and init_registers now return status
instead of panicing on failure, with their callers doing something
appropriate.

There were also duplicate declarations of save_registers and restore_registers
in os.h - these are gone.

I noticed and fixed up some whitespace damage.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 188 insertions, 102 deletions

diff --git a/arch/um/os-Linux/registers.c b/arch/um/os-Linux/registers.c
index c78fae3aba81..830fe6a1518a 100644
--- a/arch/um/os-Linux/registers.c
+++ b/arch/um/os-Linux/registers.c
@@ -8,42 +8,41 @@
 #include <string.h>
 #include <sys/ptrace.h>
 #include "sysdep/ptrace.h"
-#include "user.h"
 
-void save_registers(int pid, struct uml_pt_regs *regs)
+int save_registers(int pid, struct uml_pt_regs *regs)
 {
         int err;
 
         err = ptrace(PTRACE_GETREGS, pid, 0, regs->gp);
         if (err < 0)
-                panic("save_registers - saving registers failed, errno = %d\n",
-                      errno);
+                return -errno;
+        return 0;
 }
 
-void restore_registers(int pid, struct uml_pt_regs *regs)
+int restore_registers(int pid, struct uml_pt_regs *regs)
 {
         int err;
 
         err = ptrace(PTRACE_SETREGS, pid, 0, regs->gp);
         if (err < 0)
-                panic("restore_registers - saving registers failed, "
-                      "errno = %d\n", errno);
+                return -errno;
+        return 0;
 }
 
 /* This is set once at boot time and not changed thereafter */
 
 static unsigned long exec_regs[MAX_REG_NR];
 
-void init_registers(int pid)
+int init_registers(int pid)
 {
         int err;
 
         err = ptrace(PTRACE_GETREGS, pid, 0, exec_regs);
-        if (err)
-                panic("check_ptrace : PTRACE_GETREGS failed, errno = %d",
-                      errno);
+        if (err < 0)
+                return -errno;
 
         arch_init_registers(pid);
+        return 0;
 }
 
 void get_safe_registers(unsigned long *regs)
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 7dc24e3cb190..862fea0290ec 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -38,17 +38,17 @@ int is_skas_winch(int pid, int fd, void *data)
 
 static int ptrace_dump_regs(int pid)
 {
-        unsigned long regs[MAX_REG_NR];
-        int i;
+        unsigned long regs[MAX_REG_NR];
+        int i;
 
-        if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
-                return -errno;
+        if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
+                return -errno;
 
         printk(UM_KERN_ERR "Stub registers -\n");
         for (i = 0; i < ARRAY_SIZE(regs); i++)
                 printk(UM_KERN_ERR "\t%d - %lx\n", i, regs[i]);
 
-        return 0;
+        return 0;
 }
 
 /*
@@ -73,9 +73,11 @@ void wait_stub_done(int pid)
                         break;
 
                 err = ptrace(PTRACE_CONT, pid, 0, 0);
-                if (err)
-                        panic("wait_stub_done : continue failed, errno = %d\n",
-                              errno);
+                if (err) {
+                        printk(UM_KERN_ERR "wait_stub_done : continue failed, "
+                               "errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
         }
 
         if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
@@ -86,8 +88,10 @@ bad_wait:
         if (err)
                 printk(UM_KERN_ERR "Failed to get registers from stub, "
                        "errno = %d\n", -err);
-        panic("wait_stub_done : failed to wait for SIGUSR1/SIGTRAP, pid = %d, "
-              "n = %d, errno = %d, status = 0x%x\n", pid, n, errno, status);
+        printk(UM_KERN_ERR "wait_stub_done : failed to wait for SIGTRAP, "
+               "pid = %d, n = %d, errno = %d, status = 0x%x\n", pid, n, errno,
+               status);
+        fatal_sigsegv();
 }
 
 extern unsigned long current_stub_stack(void);
@@ -98,9 +102,11 @@ void get_skas_faultinfo(int pid, struct faultinfo * fi)
 
         if (ptrace_faultinfo) {
                 err = ptrace(PTRACE_FAULTINFO, pid, 0, fi);
-                if (err)
-                        panic("get_skas_faultinfo - PTRACE_FAULTINFO failed, "
-                              "errno = %d\n", errno);
+                if (err) {
+                        printk(UM_KERN_ERR "get_skas_faultinfo - "
+                               "PTRACE_FAULTINFO failed, errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
 
                 /* Special handling for i386, which has different structs */
                 if (sizeof(struct ptrace_faultinfo) < sizeof(struct faultinfo))
@@ -110,9 +116,11 @@ void get_skas_faultinfo(int pid, struct faultinfo * fi)
         }
         else {
                 err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
-                if (err)
-                        panic("Failed to continue stub, pid = %d, errno = %d\n",
-                              pid, errno);
+                if (err) {
+                        printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
+                               "errno = %d\n", pid, errno);
+                        fatal_sigsegv();
+                }
                 wait_stub_done(pid);
 
                 /*
@@ -145,25 +153,31 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,
         {
                 err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
                              __NR_getpid);
-                if (err < 0)
-                        panic("handle_trap - nullifying syscall failed, "
-                              "errno = %d\n", errno);
+                if (err < 0) {
+                        printk(UM_KERN_ERR "handle_trap - nullifying syscall "
+                               "failed, errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
 
                 err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
-                if (err < 0)
-                        panic("handle_trap - continuing to end of syscall "
-                              "failed, errno = %d\n", errno);
+                if (err < 0) {
+                        printk(UM_KERN_ERR "handle_trap - continuing to end of "
+                               "syscall failed, errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
 
                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
                 if ((err < 0) || !WIFSTOPPED(status) ||
-                   (WSTOPSIG(status) != SIGTRAP + 0x80)) {
-                        err = ptrace_dump_regs(pid);
-                        if (err)
-                                printk(UM_KERN_ERR "Failed to get registers "
+                    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
+                        err = ptrace_dump_regs(pid);
+                        if (err)
+                                printk(UM_KERN_ERR "Failed to get registers "
                                        "from process, errno = %d\n", -err);
-                        panic("handle_trap - failed to wait at end of syscall, "
-                              "errno = %d, status = %d\n", errno, status);
-                }
+                        printk(UM_KERN_ERR "handle_trap - failed to wait at "
+                               "end of syscall, errno = %d, status = %d\n",
+                               errno, status);
+                        fatal_sigsegv();
+                }
         }
 
         handle_syscall(regs);
@@ -181,9 +195,11 @@ static int userspace_tramp(void *stack)
         signal(SIGTERM, SIG_DFL);
         signal(SIGWINCH, SIG_IGN);
         err = set_interval();
-        if (err)
-                panic("userspace_tramp - setting timer failed, errno = %d\n",
-                      err);
+        if (err) {
+                printk(UM_KERN_ERR "userspace_tramp - setting timer failed, "
+                       "errno = %d\n", err);
+                exit(1);
+        }
 
         if (!proc_mm) {
                 /*
@@ -226,9 +242,11 @@ static int userspace_tramp(void *stack)
                 sa.sa_flags = SA_ONSTACK | SA_NODEFER;
                 sa.sa_handler = (void *) v;
                 sa.sa_restorer = NULL;
-                if (sigaction(SIGSEGV, &sa, NULL) < 0)
-                        panic("userspace_tramp - setting SIGSEGV handler "
-                              "failed - errno = %d\n", errno);
+                if (sigaction(SIGSEGV, &sa, NULL) < 0) {
+                        printk(UM_KERN_ERR "userspace_tramp - setting SIGSEGV "
+                               "handler failed - errno = %d\n", errno);
+                        exit(1);
+                }
         }
 
         kill(os_getpid(), SIGSTOP);
@@ -244,13 +262,18 @@ int start_userspace(unsigned long stub_stack)
 {
         void *stack;
         unsigned long sp;
-        int pid, status, n, flags;
+        int pid, status, n, flags, err;
 
         stack = mmap(NULL, UM_KERN_PAGE_SIZE,
                      PROT_READ | PROT_WRITE | PROT_EXEC,
                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-        if (stack == MAP_FAILED)
-                panic("start_userspace : mmap failed, errno = %d", errno);
+        if (stack == MAP_FAILED) {
+                err = -errno;
+                printk(UM_KERN_ERR "start_userspace : mmap failed, "
+                       "errno = %d", errno);
+                return err;
+        }
+
         sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 
         flags = CLONE_FILES;
@@ -260,29 +283,50 @@ int start_userspace(unsigned long stub_stack)
                 flags |= SIGCHLD;
 
         pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
-        if (pid < 0)
-                panic("start_userspace : clone failed, errno = %d", errno);
+        if (pid < 0) {
+                err = -errno;
+                printk(UM_KERN_ERR "start_userspace : clone failed, "
+                       "errno = %d", errno);
+                return err;
+        }
 
         do {
                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
-                if (n < 0)
-                        panic("start_userspace : wait failed, errno = %d",
-                              errno);
+                if (n < 0) {
+                        err = -errno;
+                        printk(UM_KERN_ERR "start_userspace : wait failed, "
+                               "errno = %d", errno);
+                        goto out_kill;
+                }
         } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGVTALRM));
 
-        if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
-                panic("start_userspace : expected SIGSTOP, got status = %d",
-                      status);
+        if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
+                err = -EINVAL;
+                printk(UM_KERN_ERR "start_userspace : expected SIGSTOP, got "
+                       "status = %d", status);
+                goto out_kill;
+        }
 
         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
-                   (void *) PTRACE_O_TRACESYSGOOD) < 0)
-                panic("start_userspace : PTRACE_OLDSETOPTIONS failed, "
-                      "errno = %d\n", errno);
+                   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
+                err = -errno;
+                printk(UM_KERN_ERR "start_userspace : PTRACE_OLDSETOPTIONS "
+                       "failed, errno = %d\n", errno);
+                goto out_kill;
+        }
 
-        if (munmap(stack, UM_KERN_PAGE_SIZE) < 0)
-                panic("start_userspace : munmap failed, errno = %d\n", errno);
+        if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
+                err = -errno;
+                printk(UM_KERN_ERR "start_userspace : munmap failed, "
+                       "errno = %d\n", errno);
+                goto out_kill;
+        }
 
         return pid;
+
+ out_kill:
+        os_kill_ptraced_process(pid, 1);
+        return err;
 }
 
 void userspace(struct uml_pt_regs *regs)
@@ -300,9 +344,16 @@ void userspace(struct uml_pt_regs *regs)
         nsecs += os_nsecs();
 
         while (1) {
+                /*
+                 * This can legitimately fail if the process loads a
+                 * bogus value into a segment register.  It will
+                 * segfault and PTRACE_GETREGS will read that value
+                 * out of the process.  However, PTRACE_SETREGS will
+                 * fail.  In this case, there is nothing to do but
+                 * just kill the process.
+                 */
                 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
-                        panic("userspace - PTRACE_SETREGS failed, "
-                              "errno = %d\n", errno);
+                        fatal_sigsegv();
 
                 /* Now we set local_using_sysemu to be used for one loop */
                 local_using_sysemu = get_using_sysemu();
@@ -310,21 +361,25 @@ void userspace(struct uml_pt_regs *regs)
                 op = SELECT_PTRACE_OPERATION(local_using_sysemu,
                                              singlestepping(NULL));
 
-                err = ptrace(op, pid, 0, 0);
-                if (err)
-                        panic("userspace - could not resume userspace process, "
-                              "pid=%d, ptrace operation = %d, errno = %d\n",
-                              pid, op, errno);
+                if (ptrace(op, pid, 0, 0)) {
+                        printk(UM_KERN_ERR "userspace - ptrace continue "
+                               "failed, op = %d, errno = %d\n", op, errno);
+                        fatal_sigsegv();
+                }
 
                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
-                if (err < 0)
-                        panic("userspace - waitpid failed, errno = %d\n",
-                              errno);
+                if (err < 0) {
+                        printk(UM_KERN_ERR "userspace - wait failed, "
+                               "errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
 
                 regs->is_user = 1;
-                if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp))
-                        panic("userspace - saving registers failed, "
-                              "errno = %d\n", errno);
+                if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
+                        printk(UM_KERN_ERR "userspace - PTRACE_GETREGS failed, "
+                               "errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
 
                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 
@@ -371,6 +426,7 @@ void userspace(struct uml_pt_regs *regs)
                         default:
                                 printk(UM_KERN_ERR "userspace - child stopped "
                                        "with signal %d\n", sig);
+                                fatal_sigsegv();
                         }
                         pid = userspace_pid[0];
                         interrupt_end();
@@ -422,9 +478,12 @@ int copy_context_skas0(unsigned long new_stack, int pid)
                                                      .it_interval = tv }) });
 
         err = ptrace_setregs(pid, thread_regs);
-        if (err < 0)
-                panic("copy_context_skas0 : PTRACE_SETREGS failed, "
-                      "pid = %d, errno = %d\n", pid, -err);
+        if (err < 0) {
+                err = -errno;
+                printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
+                       "failed, pid = %d, errno = %d\n", pid, -err);
+                return err;
+        }
 
         /* set a well known return code for detection of child write failure */
         child_data->err = 12345678;
@@ -434,31 +493,47 @@ int copy_context_skas0(unsigned long new_stack, int pid)
          * parent's stack, and check, if bad result.
          */
         err = ptrace(PTRACE_CONT, pid, 0, 0);
-        if (err)
-                panic("Failed to continue new process, pid = %d, "
-                      "errno = %d\n", pid, errno);
+        if (err) {
+                err = -errno;
+                printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
+                       "errno = %d\n", pid, errno);
+                return err;
+        }
+
         wait_stub_done(pid);
 
         pid = data->err;
-        if (pid < 0)
-                panic("copy_context_skas0 - stub-parent reports error %d\n",
-                      -pid);
+        if (pid < 0) {
+                printk(UM_KERN_ERR "copy_context_skas0 - stub-parent reports "
+                       "error %d\n", -pid);
+                return pid;
+        }
 
         /*
          * Wait, until child has finished too: read child's result from
          * child's stack and check it.
          */
         wait_stub_done(pid);
-        if (child_data->err != STUB_DATA)
-                panic("copy_context_skas0 - stub-child reports error %ld\n",
-                      child_data->err);
+        if (child_data->err != STUB_DATA) {
+                printk(UM_KERN_ERR "copy_context_skas0 - stub-child reports "
+                       "error %ld\n", child_data->err);
+                err = child_data->err;
+                goto out_kill;
+        }
 
         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
-                   (void *)PTRACE_O_TRACESYSGOOD) < 0)
-                panic("copy_context_skas0 : PTRACE_OLDSETOPTIONS failed, "
-                      "errno = %d\n", errno);
+                   (void *)PTRACE_O_TRACESYSGOOD) < 0) {
+                err = -errno;
+                printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_OLDSETOPTIONS "
+                       "failed, errno = %d\n", errno);
+                goto out_kill;
+        }
 
         return pid;
+
+ out_kill:
+        os_kill_ptraced_process(pid, 1);
+        return err;
 }
 
 /*
@@ -466,8 +541,8 @@ int copy_context_skas0(unsigned long new_stack, int pid)
  * available. Opening /proc/mm creates a new mm_context, which lacks
  * the stub-pages. Thus, we map them using /proc/mm-fd
  */
-void map_stub_pages(int fd, unsigned long code,
-                    unsigned long data, unsigned long stack)
+int map_stub_pages(int fd, unsigned long code, unsigned long data,
+                   unsigned long stack)
 {
         struct proc_mm_op mmop;
         int n;
@@ -491,8 +566,9 @@ void map_stub_pages(int fd, unsigned long code,
                 printk(UM_KERN_ERR "mmap args - addr = 0x%lx, fd = %d, "
                        "offset = %llx\n", code, code_fd,
                        (unsigned long long) code_offset);
-                panic("map_stub_pages : /proc/mm map for code failed, "
-                      "err = %d\n", n);
+                printk(UM_KERN_ERR "map_stub_pages : /proc/mm map for code "
+                       "failed, err = %d\n", n);
+                return -n;
         }
 
         if (stack) {
@@ -510,10 +586,15 @@ void map_stub_pages(int fd, unsigned long code,
                                       .offset  = map_offset
                 } } });
                 CATCH_EINTR(n = write(fd, &mmop, sizeof(mmop)));
-                if (n != sizeof(mmop))
-                        panic("map_stub_pages : /proc/mm map for data failed, "
-                              "err = %d\n", errno);
+                if (n != sizeof(mmop)) {
+                        n = errno;
+                        printk(UM_KERN_ERR "map_stub_pages : /proc/mm map for "
+                               "data failed, err = %d\n", n);
+                        return -n;
+                }
         }
+
+        return 0;
 }
 
 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
@@ -574,7 +655,9 @@ int start_idle_thread(void *stack, jmp_buf *switch_buf)
                 kmalloc_ok = 0;
                 return 1;
         default:
-                panic("Bad sigsetjmp return in start_idle_thread - %d\n", n);
+                printk(UM_KERN_ERR "Bad sigsetjmp return in "
+                       "start_idle_thread - %d\n", n);
+                fatal_sigsegv();
         }
         longjmp(*switch_buf, 1);
 }
@@ -617,9 +700,11 @@ void __switch_mm(struct mm_id *mm_idp)
         if (proc_mm) {
                 err = ptrace(PTRACE_SWITCH_MM, userspace_pid[0], 0,
                              mm_idp->u.mm_fd);
-                if (err)
-                        panic("__switch_mm - PTRACE_SWITCH_MM failed, "
-                              "errno = %d\n", errno);
+                if (err) {
+                        printk(UM_KERN_ERR "__switch_mm - PTRACE_SWITCH_MM "
+                               "failed, errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
         }
         else userspace_pid[0] = mm_idp->u.pid;
 }
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index b07887c36bb0..6d56d15884fd 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -411,7 +411,9 @@ static inline void check_skas3_ptrace_faultinfo(void)
                         non_fatal("found\n");
         }
 
-        init_registers(pid);
+        if (init_registers(pid))
+                fatal("Failed to initialize default registers");
+
         stop_ptraced_child(pid, 1, 1);
 }