/* Linux-specific ptrace manipulation routines. Copyright (C) 2012-2015 Free Software Foundation, Inc. This file is part of GDB. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ #include "common-defs.h" #include "linux-ptrace.h" #include "linux-procfs.h" #include "linux-waitpid.h" #include "buffer.h" #include "gdb_wait.h" #include /* Stores the currently supported ptrace options. A value of -1 means we did not check for features yet. A value of 0 means there are no supported features. */ static int current_ptrace_options = -1; /* Additional flags to test. */ static int additional_flags; /* Find all possible reasons we could fail to attach PID and append these as strings to the already initialized BUFFER. '\0' termination of BUFFER must be done by the caller. */ void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer) { pid_t tracerpid; tracerpid = linux_proc_get_tracerpid_nowarn (pid); if (tracerpid > 0) buffer_xml_printf (buffer, _("process %d is already traced " "by process %d"), (int) pid, (int) tracerpid); if (linux_proc_pid_is_zombie_nowarn (pid)) buffer_xml_printf (buffer, _("process %d is a zombie " "- the process has already terminated"), (int) pid); } /* See linux-ptrace.h. */ char * linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err) { static char *reason_string; struct buffer buffer; char *warnings; long lwpid = ptid_get_lwp (ptid); xfree (reason_string); buffer_init (&buffer); linux_ptrace_attach_fail_reason (lwpid, &buffer); buffer_grow_str0 (&buffer, ""); warnings = buffer_finish (&buffer); if (warnings[0] != '\0') reason_string = xstrprintf ("%s (%d), %s", safe_strerror (err), err, warnings); else reason_string = xstrprintf ("%s (%d)", safe_strerror (err), err); xfree (warnings); return reason_string; } #if defined __i386__ || defined __x86_64__ /* Address of the 'ret' instruction in asm code block below. */ extern void (linux_ptrace_test_ret_to_nx_instr) (void); #include #include #include #endif /* defined __i386__ || defined __x86_64__ */ /* Test broken off-trunk Linux kernel patchset for NX support on i386. It was removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd. Test also x86_64 arch for PaX support. */ static void linux_ptrace_test_ret_to_nx (void) { #if defined __i386__ || defined __x86_64__ pid_t child, got_pid; gdb_byte *return_address, *pc; long l; int status, kill_status; return_address = mmap (NULL, 2, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (return_address == MAP_FAILED) { warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"), safe_strerror (errno)); return; } /* Put there 'int3'. */ *return_address = 0xcc; child = fork (); switch (child) { case -1: warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"), safe_strerror (errno)); return; case 0: l = ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) NULL, (PTRACE_TYPE_ARG4) NULL); if (l != 0) warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"), safe_strerror (errno)); else { #if defined __i386__ asm volatile ("pushl %0;" ".globl linux_ptrace_test_ret_to_nx_instr;" "linux_ptrace_test_ret_to_nx_instr:" "ret" : : "r" (return_address) : "%esp", "memory"); #elif defined __x86_64__ asm volatile ("pushq %0;" ".globl linux_ptrace_test_ret_to_nx_instr;" "linux_ptrace_test_ret_to_nx_instr:" "ret" : : "r" ((uint64_t) (uintptr_t) return_address) : "%rsp", "memory"); #else # error "!__i386__ && !__x86_64__" #endif gdb_assert_not_reached ("asm block did not terminate"); } _exit (1); } errno = 0; got_pid = waitpid (child, &status, 0); if (got_pid != child) { warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"), (long) got_pid, safe_strerror (errno)); return; } if (WIFSIGNALED (status)) { if (WTERMSIG (status) != SIGKILL) warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"), (int) WTERMSIG (status)); else warning (_("Cannot call inferior functions, Linux kernel PaX " "protection forbids return to non-executable pages!")); return; } if (!WIFSTOPPED (status)) { warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"), status); return; } /* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */ if (WSTOPSIG (status) != SIGTRAP && WSTOPSIG (status) != SIGSEGV) { warning (_("linux_ptrace_test_ret_to_nx: " "WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"), (int) WSTOPSIG (status)); return; } errno = 0; #if defined __i386__ l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (EIP * 4), (PTRACE_TYPE_ARG4) NULL); #elif defined __x86_64__ l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (RIP * 8), (PTRACE_TYPE_ARG4) NULL); #else # error "!__i386__ && !__x86_64__" #endif if (errno != 0) { warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"), safe_strerror (errno)); return; } pc = (void *) (uintptr_t) l; kill (child, SIGKILL); ptrace (PTRACE_KILL, child, (PTRACE_TYPE_ARG3) NULL, (PTRACE_TYPE_ARG4) NULL); errno = 0; got_pid = waitpid (child, &kill_status, 0); if (got_pid != child) { warning (_("linux_ptrace_test_ret_to_nx: " "PTRACE_KILL waitpid returned %ld: %s"), (long) got_pid, safe_strerror (errno)); return; } if (!WIFSIGNALED (kill_status)) { warning (_("linux_ptrace_test_ret_to_nx: " "PTRACE_KILL status %d is not WIFSIGNALED!"), status); return; } /* + 1 is there as x86* stops after the 'int3' instruction. */ if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1) { /* PASS */ return; } /* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */ if (WSTOPSIG (status) == SIGSEGV && pc == return_address) { /* PASS */ return; } if ((void (*) (void)) pc != &linux_ptrace_test_ret_to_nx_instr) warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return " "address %p nor is the return instruction %p!"), pc, return_address, &linux_ptrace_test_ret_to_nx_instr); else warning (_("Cannot call inferior functions on this system - " "Linux kernel with broken i386 NX (non-executable pages) " "support detected!")); #endif /* defined __i386__ || defined __x86_64__ */ } /* Helper function to fork a process and make the child process call the function FUNCTION, passing CHILD_STACK as parameter. For MMU-less targets, clone is used instead of fork, and CHILD_STACK is used as stack space for the cloned child. If NULL, stack space is allocated via malloc (and subsequently passed to FUNCTION). For MMU targets, CHILD_STACK is ignored. */ static int linux_fork_to_function (gdb_byte *child_stack, void (*function) (gdb_byte *)) { int child_pid; /* Sanity check the function pointer. */ gdb_assert (function != NULL); #if defined(__UCLIBC__) && defined(HAS_NOMMU) #define STACK_SIZE 4096 if (child_stack == NULL) child_stack = xmalloc (STACK_SIZE * 4); /* Use CLONE_VM instead of fork, to support uClinux (no MMU). */ #ifdef __ia64__ child_pid = __clone2 (function, child_stack, STACK_SIZE, CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2); #else /* !__ia64__ */ child_pid = clone (function, child_stack + STACK_SIZE, CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2); #endif /* !__ia64__ */ #else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */ child_pid = fork (); if (child_pid == 0) function (NULL); #endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */ if (child_pid == -1) perror_with_name (("fork")); return child_pid; } /* A helper function for linux_check_ptrace_features, called after the child forks a grandchild. */ static void linux_grandchild_function (gdb_byte *child_stack) { /* Free any allocated stack. */ xfree (child_stack); /* This code is only reacheable by the grandchild (child's child) process. */ _exit (0); } /* A helper function for linux_check_ptrace_features, called after the parent process forks a child. The child allows itself to be traced by its parent. */ static void linux_child_function (gdb_byte *child_stack) { ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0); kill (getpid (), SIGSTOP); /* Fork a grandchild. */ linux_fork_to_function (child_stack, linux_grandchild_function); /* This code is only reacheable by the child (grandchild's parent) process. */ _exit (0); } static void linux_test_for_tracesysgood (int child_pid); static void linux_test_for_tracefork (int child_pid); static void linux_test_for_exitkill (int child_pid); /* Determine ptrace features available on this target. */ static void linux_check_ptrace_features (void) { int child_pid, ret, status; /* Initialize the options. */ current_ptrace_options = 0; /* Fork a child so we can do some testing. The child will call linux_child_function and will get traced. The child will eventually fork a grandchild so we can test fork event reporting. */ child_pid = linux_fork_to_function (NULL, linux_child_function); ret = my_waitpid (child_pid, &status, 0); if (ret == -1) perror_with_name (("waitpid")); else if (ret != child_pid) error (_("linux_check_ptrace_features: waitpid: unexpected result %d."), ret); if (! WIFSTOPPED (status)) error (_("linux_check_ptrace_features: waitpid: unexpected status %d."), status); linux_test_for_tracesysgood (child_pid); linux_test_for_tracefork (child_pid); linux_test_for_exitkill (child_pid); /* Clean things up and kill any pending children. */ do { ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0); if (ret != 0) warning (_("linux_check_ptrace_features: failed to kill child")); my_waitpid (child_pid, &status, 0); } while (WIFSTOPPED (status)); } /* Determine if PTRACE_O_TRACESYSGOOD can be used to catch syscalls. */ static void linux_test_for_tracesysgood (int child_pid) { int ret; if ((additional_flags & PTRACE_O_TRACESYSGOOD) == 0) return; ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) PTRACE_O_TRACESYSGOOD); if (ret == 0) current_ptrace_options |= PTRACE_O_TRACESYSGOOD; } /* Determine if PTRACE_O_TRACEFORK can be used to follow fork events. */ static void linux_test_for_tracefork (int child_pid) { int ret, status; long second_pid; /* First, set the PTRACE_O_TRACEFORK option. If this fails, we know for sure that it is not supported. */ ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) PTRACE_O_TRACEFORK); if (ret != 0) return; if ((additional_flags & PTRACE_O_TRACEVFORKDONE) != 0) { /* Check if the target supports PTRACE_O_TRACEVFORKDONE. */ ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) (PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORKDONE)); if (ret == 0) current_ptrace_options |= PTRACE_O_TRACEVFORKDONE; } /* Setting PTRACE_O_TRACEFORK did not cause an error, however we don't know for sure that the feature is available; old versions of PTRACE_SETOPTIONS ignored unknown options. Therefore, we attach to the child process, use PTRACE_SETOPTIONS to enable fork tracing, and let it fork. If the process exits, we assume that we can't use PTRACE_O_TRACEFORK; if we get the fork notification, and we can extract the new child's PID, then we assume that we can. We do not explicitly check for vfork tracing here. It is assumed that vfork tracing is available whenever fork tracing is available. */ ret = ptrace (PTRACE_CONT, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0); if (ret != 0) warning (_("linux_test_for_tracefork: failed to resume child")); ret = my_waitpid (child_pid, &status, 0); /* Check if we received a fork event notification. */ if (ret == child_pid && WIFSTOPPED (status) && linux_ptrace_get_extended_event (status) == PTRACE_EVENT_FORK) { /* We did receive a fork event notification. Make sure its PID is reported. */ second_pid = 0; ret = ptrace (PTRACE_GETEVENTMSG, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) &second_pid); if (ret == 0 && second_pid != 0) { int second_status; /* We got the PID from the grandchild, which means fork tracing is supported. */ current_ptrace_options |= PTRACE_O_TRACECLONE; current_ptrace_options |= (additional_flags & (PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACEEXEC)); /* Do some cleanup and kill the grandchild. */ my_waitpid (second_pid, &second_status, 0); ret = ptrace (PTRACE_KILL, second_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0); if (ret != 0) warning (_("linux_test_for_tracefork: " "failed to kill second child")); my_waitpid (second_pid, &status, 0); } } else warning (_("linux_test_for_tracefork: unexpected result from waitpid " "(%d, status 0x%x)"), ret, status); } /* Determine if PTRACE_O_EXITKILL can be used. */ static void linux_test_for_exitkill (int child_pid) { int ret; ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) PTRACE_O_EXITKILL); if (ret == 0) current_ptrace_options |= PTRACE_O_EXITKILL; } /* Enable reporting of all currently supported ptrace events. ATTACHED should be nonzero if we have attached to the inferior. */ void linux_enable_event_reporting (pid_t pid, int attached) { int ptrace_options; /* Check if we have initialized the ptrace features for this target. If not, do it now. */ if (current_ptrace_options == -1) linux_check_ptrace_features (); ptrace_options = current_ptrace_options; if (attached) { /* When attached to our inferior, we do not want the inferior to die with us if we terminate unexpectedly. */ ptrace_options &= ~PTRACE_O_EXITKILL; } /* Set the options. */ ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) (uintptr_t) ptrace_options); } /* Disable reporting of all currently supported ptrace events. */ void linux_disable_event_reporting (pid_t pid) { /* Set the options. */ ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0, 0); } /* Returns non-zero if PTRACE_OPTIONS is contained within CURRENT_PTRACE_OPTIONS, therefore supported. Returns 0 otherwise. */ static int ptrace_supports_feature (int ptrace_options) { if (current_ptrace_options == -1) linux_check_ptrace_features (); return ((current_ptrace_options & ptrace_options) == ptrace_options); } /* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace, 0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK, since they were all added to the kernel at the same time. */ int linux_supports_tracefork (void) { return ptrace_supports_feature (PTRACE_O_TRACEFORK); } /* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace, 0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK, since they were all added to the kernel at the same time. */ int linux_supports_traceclone (void) { return ptrace_supports_feature (PTRACE_O_TRACECLONE); } /* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by ptrace, 0 otherwise. */ int linux_supports_tracevforkdone (void) { return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE); } /* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace, 0 otherwise. */ int linux_supports_tracesysgood (void) { return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD); } /* Display possible problems on this system. Display them only once per GDB execution. */ void linux_ptrace_init_warnings (void) { static int warned = 0; if (warned) return; warned = 1; linux_ptrace_test_ret_to_nx (); } /* Set additional ptrace flags to use. Some such flags may be checked by the implementation above. This function must be called before any other function in this file; otherwise the flags may not take effect appropriately. */ void linux_ptrace_set_additional_flags (int flags) { additional_flags = flags; } /* Extract extended ptrace event from wait status. */ int linux_ptrace_get_extended_event (int wstat) { return (wstat >> 16); } /* Determine whether wait status denotes an extended event. */ int linux_is_extended_waitstatus (int wstat) { return (linux_ptrace_get_extended_event (wstat) != 0); }