Avoid backtrace from __stack_chk_fail [BZ #12189]

  On Mon, Jul 10, 2017 at 1:14 PM, Joseph Myers <joseph@codesourcery.com> wrote:
> On Mon, 10 Jul 2017, H.J. Lu wrote:
>
>> diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
>> new file mode 100644
>> index 0000000..14d8e26
>> --- /dev/null
>> +++ b/debug/tst-ssp-1.c
>> @@ -0,0 +1,40 @@
>> +/* Copyright (C) 2017 Free Software Foundation, Inc.
>
> All new files should have a descriptive comment on their first line,
> before the copyright notice.
>

Here is the updated patch.   OK for master?
  

On 10/07/2017 17:21, H.J. Lu wrote:
> On Mon, Jul 10, 2017 at 1:14 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>> On Mon, 10 Jul 2017, H.J. Lu wrote:
>>
>>> diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
>>> new file mode 100644
>>> index 0000000..14d8e26
>>> --- /dev/null
>>> +++ b/debug/tst-ssp-1.c
>>> @@ -0,0 +1,40 @@
>>> +/* Copyright (C) 2017 Free Software Foundation, Inc.
>> All new files should have a descriptive comment on their first line,
>> before the copyright notice.
>>
> Here is the updated patch.   OK for master?
> 
> 
> -- H.J.
> 
> 
> 0001-Avoid-backtrace-from-__stack_chk_fail-BZ-12189.patch
> 
> 
> From 63fc15cbda7fcdeb5e8dcc44c416b6a330cbbf70 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Mon, 10 Jul 2017 12:21:39 -0700
> Subject: [PATCH] Avoid backtrace from __stack_chk_fail [BZ #12189]
> 
> __stack_chk_fail is called on corrupted stack.  __stack_chk_fail should
> use as little stack as possible.  __libc_message is extended to avoid
> calling BEFORE_ABORT when do_abort >= 3 and __fortify_fail_abort is
> added to avoid backtrace from __stack_chk_fail.
> 
> 	[BZ #12189]
> 	* debug/Makefile (CFLAGS-tst-ssp-1.c): New.
> 	(tests): Add tst-ssp-1 if -fstack-protector works.
> 	* debug/fortify_fail.c (_fortify_fail_abort): New function.
> 	(__fortify_fail): Call _fortify_fail_abort.
> 	(__fortify_fail_abort): Add a hidden definition.
> 	* debug/stack_chk_fail.c (__stack_chk_fail): Call
> 	__fortify_fail_abort, instead of __fortify_fail.
> 	* debug/tst-ssp-1.c: New file.
> 	* include/stdio.h (__fortify_fail_abort): New hidden prototype.
> 	* sysdeps/posix/libc_fatal.c (__libc_message): Call BEFORE_ABORT
> 	if do_abort < 3.
> ---
>  debug/Makefile             |  7 +++++++
>  debug/fortify_fail.c       | 13 +++++++++++--
>  debug/stack_chk_fail.c     |  2 +-
>  debug/tst-ssp-1.c          | 39 +++++++++++++++++++++++++++++++++++++++
>  include/stdio.h            |  3 +++
>  sysdeps/posix/libc_fatal.c |  3 ++-
>  6 files changed, 63 insertions(+), 4 deletions(-)
>  create mode 100644 debug/tst-ssp-1.c
> 
> diff --git a/debug/Makefile b/debug/Makefile
> index cd4975c..10f9dea 100644
> --- a/debug/Makefile
> +++ b/debug/Makefile
> @@ -139,12 +139,19 @@ LDFLAGS-tst-backtrace4 = -rdynamic
>  LDFLAGS-tst-backtrace5 = -rdynamic
>  LDFLAGS-tst-backtrace6 = -rdynamic
>  
> +CFLAGS-tst-ssp-1.c = -Wno-format -Wno-deprecated-declarations -Wno-error \
> +		     -O0 -fstack-protector

Why explicit -O0 here?

> +
>  tests = backtrace-tst tst-longjmp_chk tst-chk1 tst-chk2 tst-chk3 \
>  	tst-lfschk1 tst-lfschk2 tst-lfschk3 test-strcpy_chk test-stpcpy_chk \
>  	tst-chk4 tst-chk5 tst-chk6 tst-lfschk4 tst-lfschk5 tst-lfschk6 \
>  	tst-longjmp_chk2 tst-backtrace2 tst-backtrace3 tst-backtrace4 \
>  	tst-backtrace5 tst-backtrace6
>  
> +ifeq ($(have-ssp),yes)
> +tests += tst-ssp-1
> +endif
> +
>  ifeq (,$(CXX))
>  tests-unsupported = tst-chk4 tst-chk5 tst-chk6 \
>  		    tst-lfschk4 tst-lfschk5 tst-lfschk6
> diff --git a/debug/fortify_fail.c b/debug/fortify_fail.c
> index a31977a..13063bf 100644
> --- a/debug/fortify_fail.c
> +++ b/debug/fortify_fail.c
> @@ -23,11 +23,20 @@ extern char **__libc_argv attribute_hidden;
>  
>  void
>  __attribute__ ((noreturn)) internal_function
> -__fortify_fail (const char *msg)
> +__fortify_fail_abort (int no_backtrace, const char *msg)

Would be better to use bool since it is an internal function?

>  {
>    /* The loop is added only to keep gcc happy.  */
>    while (1)
> -    __libc_message (2, "*** %s ***: %s terminated\n",
> +    __libc_message (no_backtrace ? 3 : 2, "*** %s ***: %s terminated\n",
>  		    msg, __libc_argv[0] ?: "<unknown>");
>  }
> +
> +void
> +__attribute__ ((noreturn)) internal_function
> +__fortify_fail (const char *msg)
> +{
> +  __fortify_fail_abort (0, msg);
> +}
> +
>  libc_hidden_def (__fortify_fail)
> +libc_hidden_def (__fortify_fail_abort)
> diff --git a/debug/stack_chk_fail.c b/debug/stack_chk_fail.c
> index 120d269..2f39e43 100644
> --- a/debug/stack_chk_fail.c
> +++ b/debug/stack_chk_fail.c
> @@ -25,7 +25,7 @@ void
>  __attribute__ ((noreturn))
>  __stack_chk_fail (void)
>  {
> -  __fortify_fail ("stack smashing detected");
> +  __fortify_fail_abort (1, "stack smashing detected");
>  }
>  
>  #ifdef SHARED
> diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
> new file mode 100644
> index 0000000..789b035
> --- /dev/null
> +++ b/debug/tst-ssp-1.c
> @@ -0,0 +1,39 @@
> +/* Verify that __stack_chk_fail won't segfault. 
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library 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
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +/* Based on gcc.dg/ssp-1.c from GCC testsuite.  */
> +
> +#include <signal.h>
> +
> +static int do_test (void);
> +#define TEST_FUNCTION do_test ()
> +#define EXPECTED_SIGNAL SIGABRT
> +#include "../test-skeleton.c"

Use libsupport.

> +
> +static int
> +do_test (void)
> +{
> +  int i;
> +  char foo[30];
> +
> +  // smash stack
> +  for (i = 0; i <= 400; i++)
> +    foo[i] = 42;
> +
> +  return 1; /* fail */
> +}
> diff --git a/include/stdio.h b/include/stdio.h
> index f68f633..31dc7a6 100644
> --- a/include/stdio.h
> +++ b/include/stdio.h
> @@ -92,7 +92,10 @@ extern void __libc_fatal (const char *__message)
>  extern void __libc_message (int do_abort, const char *__fnt, ...);
>  extern void __fortify_fail (const char *msg)
>       __attribute__ ((__noreturn__)) internal_function;
> +extern void __fortify_fail_abort (int, const char *msg)
> +     __attribute__ ((__noreturn__)) internal_function;
>  libc_hidden_proto (__fortify_fail)
> +libc_hidden_proto (__fortify_fail_abort)
>  
>  /* Acquire ownership of STREAM.  */
>  extern void __flockfile (FILE *__stream);
> diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
> index b261963..a0cd8b2 100644
> --- a/sysdeps/posix/libc_fatal.c
> +++ b/sysdeps/posix/libc_fatal.c
> @@ -169,7 +169,8 @@ __libc_message (int do_abort, const char *fmt, ...)
>  
>    if (do_abort)
>      {
> -      BEFORE_ABORT (do_abort, written, fd);
> +      if (do_abort < 3)
> +	BEFORE_ABORT (do_abort, written, fd);
>  
>        /* Kill the application.  */
>        abort ();
> -- 2.9.4
>
  

On Mon, Jul 10, 2017 at 1:39 PM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
> On 10/07/2017 17:21, H.J. Lu wrote:
>> On Mon, Jul 10, 2017 at 1:14 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>>> On Mon, 10 Jul 2017, H.J. Lu wrote:
>>>
>>>> diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
>>>> new file mode 100644
>>>> index 0000000..14d8e26
>>>> --- /dev/null
>>>> +++ b/debug/tst-ssp-1.c
>>>> @@ -0,0 +1,40 @@
>>>> +/* Copyright (C) 2017 Free Software Foundation, Inc.
>>> All new files should have a descriptive comment on their first line,
>>> before the copyright notice.
>>>
>> Here is the updated patch.   OK for master?
>>
>>
>> -- H.J.
>>
>>
>> 0001-Avoid-backtrace-from-__stack_chk_fail-BZ-12189.patch
>>
>>
>> From 63fc15cbda7fcdeb5e8dcc44c416b6a330cbbf70 Mon Sep 17 00:00:00 2001
>> From: "H.J. Lu" <hjl.tools@gmail.com>
>> Date: Mon, 10 Jul 2017 12:21:39 -0700
>> Subject: [PATCH] Avoid backtrace from __stack_chk_fail [BZ #12189]
>>
>> __stack_chk_fail is called on corrupted stack.  __stack_chk_fail should
>> use as little stack as possible.  __libc_message is extended to avoid
>> calling BEFORE_ABORT when do_abort >= 3 and __fortify_fail_abort is
>> added to avoid backtrace from __stack_chk_fail.
>>
>>       [BZ #12189]
>>       * debug/Makefile (CFLAGS-tst-ssp-1.c): New.
>>       (tests): Add tst-ssp-1 if -fstack-protector works.
>>       * debug/fortify_fail.c (_fortify_fail_abort): New function.
>>       (__fortify_fail): Call _fortify_fail_abort.
>>       (__fortify_fail_abort): Add a hidden definition.
>>       * debug/stack_chk_fail.c (__stack_chk_fail): Call
>>       __fortify_fail_abort, instead of __fortify_fail.
>>       * debug/tst-ssp-1.c: New file.
>>       * include/stdio.h (__fortify_fail_abort): New hidden prototype.
>>       * sysdeps/posix/libc_fatal.c (__libc_message): Call BEFORE_ABORT
>>       if do_abort < 3.
>> ---
>>  debug/Makefile             |  7 +++++++
>>  debug/fortify_fail.c       | 13 +++++++++++--
>>  debug/stack_chk_fail.c     |  2 +-
>>  debug/tst-ssp-1.c          | 39 +++++++++++++++++++++++++++++++++++++++
>>  include/stdio.h            |  3 +++
>>  sysdeps/posix/libc_fatal.c |  3 ++-
>>  6 files changed, 63 insertions(+), 4 deletions(-)
>>  create mode 100644 debug/tst-ssp-1.c
>>
>> diff --git a/debug/Makefile b/debug/Makefile
>> index cd4975c..10f9dea 100644
>> --- a/debug/Makefile
>> +++ b/debug/Makefile
>> @@ -139,12 +139,19 @@ LDFLAGS-tst-backtrace4 = -rdynamic
>>  LDFLAGS-tst-backtrace5 = -rdynamic
>>  LDFLAGS-tst-backtrace6 = -rdynamic
>>
>> +CFLAGS-tst-ssp-1.c = -Wno-format -Wno-deprecated-declarations -Wno-error \
>> +                  -O0 -fstack-protector
>
> Why explicit -O0 here?

GCC 6.3 may optimize out __stack_chk_fail:

[hjl@gnu-6 tmp]$ cat ssp-1.c
int main (void)
{
  int i = 0;
  char foo[30];

  /* Overflow buffer.  */
  for (i = 0; i < 400; i++)
    foo[i] = 42;

  return 1; /* fail */
}
[hjl@gnu-6 tmp]$ gcc -S -O2 -fstack-protector ssp-1.c
ssp-1.c: In function ‘main’:
ssp-1.c:8:12: warning: iteration 30 invokes undefined behavior
[-Waggressive-loop-optimizations]
     foo[i] = 42;
     ~~~~~~~^~~~
ssp-1.c:7:3: note: within this loop
   for (i = 0; i < 400; i++)
   ^~~
[hjl@gnu-6 tmp]$ cat ssp-1.s
.file "ssp-1.c"
.section .text.startup,"ax",@progbits
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB0:
.cfi_startproc
movl $1, %eax
ret
.cfi_endproc
.LFE0:
.size main, .-main
.ident "GCC: (GNU) 6.3.1 20170216 (Red Hat 6.3.1-3)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-6 tmp]$

>> +
>>  tests = backtrace-tst tst-longjmp_chk tst-chk1 tst-chk2 tst-chk3 \
>>       tst-lfschk1 tst-lfschk2 tst-lfschk3 test-strcpy_chk test-stpcpy_chk \
>>       tst-chk4 tst-chk5 tst-chk6 tst-lfschk4 tst-lfschk5 tst-lfschk6 \
>>       tst-longjmp_chk2 tst-backtrace2 tst-backtrace3 tst-backtrace4 \
>>       tst-backtrace5 tst-backtrace6
>>
>> +ifeq ($(have-ssp),yes)
>> +tests += tst-ssp-1
>> +endif
>> +
>>  ifeq (,$(CXX))
>>  tests-unsupported = tst-chk4 tst-chk5 tst-chk6 \
>>                   tst-lfschk4 tst-lfschk5 tst-lfschk6
>> diff --git a/debug/fortify_fail.c b/debug/fortify_fail.c
>> index a31977a..13063bf 100644
>> --- a/debug/fortify_fail.c
>> +++ b/debug/fortify_fail.c
>> @@ -23,11 +23,20 @@ extern char **__libc_argv attribute_hidden;
>>
>>  void
>>  __attribute__ ((noreturn)) internal_function
>> -__fortify_fail (const char *msg)
>> +__fortify_fail_abort (int no_backtrace, const char *msg)
>
> Would be better to use bool since it is an internal function?

I thought about it.  I wanted to avoid including <stdbool.h> in
include/stdio.h.  I can add it if it is desirable.

>>  {
>>    /* The loop is added only to keep gcc happy.  */
>>    while (1)
>> -    __libc_message (2, "*** %s ***: %s terminated\n",
>> +    __libc_message (no_backtrace ? 3 : 2, "*** %s ***: %s terminated\n",
>>                   msg, __libc_argv[0] ?: "<unknown>");
>>  }
>> +
>> +void
>> +__attribute__ ((noreturn)) internal_function
>> +__fortify_fail (const char *msg)
>> +{
>> +  __fortify_fail_abort (0, msg);
>> +}
>> +
>>  libc_hidden_def (__fortify_fail)
>> +libc_hidden_def (__fortify_fail_abort)
>> diff --git a/debug/stack_chk_fail.c b/debug/stack_chk_fail.c
>> index 120d269..2f39e43 100644
>> --- a/debug/stack_chk_fail.c
>> +++ b/debug/stack_chk_fail.c
>> @@ -25,7 +25,7 @@ void
>>  __attribute__ ((noreturn))
>>  __stack_chk_fail (void)
>>  {
>> -  __fortify_fail ("stack smashing detected");
>> +  __fortify_fail_abort (1, "stack smashing detected");
>>  }
>>
>>  #ifdef SHARED
>> diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
>> new file mode 100644
>> index 0000000..789b035
>> --- /dev/null
>> +++ b/debug/tst-ssp-1.c
>> @@ -0,0 +1,39 @@
>> +/* Verify that __stack_chk_fail won't segfault.
>> +   Copyright (C) 2017 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library 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
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <http://www.gnu.org/licenses/>.  */
>> +
>> +/* Based on gcc.dg/ssp-1.c from GCC testsuite.  */
>> +
>> +#include <signal.h>
>> +
>> +static int do_test (void);
>> +#define TEST_FUNCTION do_test ()
>> +#define EXPECTED_SIGNAL SIGABRT
>> +#include "../test-skeleton.c"
>
> Use libsupport.

I will take a look.

>> +
>> +static int
>> +do_test (void)
>> +{
>> +  int i;
>> +  char foo[30];
>> +
>> +  // smash stack
>> +  for (i = 0; i <= 400; i++)
>> +    foo[i] = 42;
>> +
>> +  return 1; /* fail */
>> +}
>> diff --git a/include/stdio.h b/include/stdio.h
>> index f68f633..31dc7a6 100644
>> --- a/include/stdio.h
>> +++ b/include/stdio.h
>> @@ -92,7 +92,10 @@ extern void __libc_fatal (const char *__message)
>>  extern void __libc_message (int do_abort, const char *__fnt, ...);
>>  extern void __fortify_fail (const char *msg)
>>       __attribute__ ((__noreturn__)) internal_function;
>> +extern void __fortify_fail_abort (int, const char *msg)
>> +     __attribute__ ((__noreturn__)) internal_function;
>>  libc_hidden_proto (__fortify_fail)
>> +libc_hidden_proto (__fortify_fail_abort)
>>
>>  /* Acquire ownership of STREAM.  */
>>  extern void __flockfile (FILE *__stream);
>> diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
>> index b261963..a0cd8b2 100644
>> --- a/sysdeps/posix/libc_fatal.c
>> +++ b/sysdeps/posix/libc_fatal.c
>> @@ -169,7 +169,8 @@ __libc_message (int do_abort, const char *fmt, ...)
>>
>>    if (do_abort)
>>      {
>> -      BEFORE_ABORT (do_abort, written, fd);
>> +      if (do_abort < 3)
>> +     BEFORE_ABORT (do_abort, written, fd);
>>
>>        /* Kill the application.  */
>>        abort ();
>> -- 2.9.4
>>
  

* H. J. Lu:

>> Would be better to use bool since it is an internal function?
>
> I thought about it.  I wanted to avoid including <stdbool.h> in
> include/stdio.h.  I can add it if it is desirable.

You could use _Bool if that's a concern.
  

* Adhemerval Zanella:

>> +CFLAGS-tst-ssp-1.c = -Wno-format -Wno-deprecated-declarations -Wno-error \
>> +		     -O0 -fstack-protector
>
> Why explicit -O0 here?

The test case is invalid C because it writes out of bounds, and newer
compiler versions can see that.  I'd suggest to use
-fstack-protector-all and a memory barrier instead (along with
comments).  That should mean that none of the -W flags are necessary,
either.