[2/2] Add an x86 IFUNC testcase for [BZ #20019]
Commit Message
On Wed, Oct 12, 2016 at 3:19 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Oct 11, 2016 at 10:45 PM, Carlos O'Donell <carlos@redhat.com> wrote:
>> On 10/05/2016 02:16 PM, H.J. Lu wrote:
>>> On Tue, Oct 4, 2016 at 5:09 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>>>> On Wed, 5 Oct 2016, H.J. Lu wrote:
>>>>
>>>>> I can try __builtin_memcpy, instread of __builtin_memmove. There are 2
>>>
>>> I changed it to use __builtin_memset.
>>>
>>>>> acceptable results. One is ld.so issues an error and the other is program runs.
>>>>> On x86, ld.so issues an error. I don't know what should happen on others.
>>>>
>>>> You could make the test pass on either of those results (while failing if
>>>> ld.so crashes).
>>>>
>>>
>>> I moved the test to elf. It passes if the test runs or ld.so issues an
>>> error. Please try it on arm, powerpc and s390.
>>
>> This is the wrong way to test this.
>>
>> The point of this test is this:
>>
>> - Verify that an unversioned symbol reference in DSO A which has no DT_NEEDED
>> on DSO B, when resolved to a symbol definition in DSO B, when the symbol in
>> DSO B is an IFUNC with a resolver, that DSO B is relocated _before_ the IFUNC
>> resolver is called, because DSO B's resolver might need global data to make
>> the IFUNC decision e.g. GOT setup.
>>
>> The invariant we want to hold true for IFUNC is that to call the resolver
>> function you must have relocated the DSO which contains the resolver. This _should_
>> have been done by a symbol reocation dependency analysis, but that isn't working
>> correctly IMO or needs deeper analysis in the dynamic loader.
>>
>> The solution we want in place today is to issue some kind of diagnostic until we
>> fix the real problem.
>>
>> The test should look like this:
>>
>> - DSO A with an unversioned symbol reference to 'foo'.
>> - DSO B with a symbol definition of 'foo' as an ifunc with 'foo_resolver' as the
>> resolver function which references global data from DSO C to decide which of
>> two functions to return.
>> - DSO C with global data set to a value.
>>
>> The point is that DSO B depends on DSO C and has DT_NEEDED on it, so C will get
>> relocated first, then B, such that B's GOT is setup to access C's global data.
>>
>> When handling the reference to 'foo' in DSO A we should on x86_64 and i686
>> get the error about needing to relink DSO A so it depends on DSO B, to form
>> the initialization order of C->B->A.
>>
>> I expect this test case will now crash the other arches, rather than just
>> avoiding the crash by relying on internal libc.so details about which ifuncs
>> you're using.
>>
>> This is one step towards a better definition of IFUNC semantics, which need to
>> be more clearly defined (something I wish I had time to define and fix so
>> more projects could use them).
>
> IFUNC resolver can fail for various reasons. My goal is to make sure
> that IFUNC inside of glibc works correctly or an error message is given
> when glibc isn't used properly. In case of x86, CPU feature info is
> retrieved and stored in ld.so very early at startup, which is used by IFUNC
> and only accessible in libc.so and libm.so after they have been relocated.
> My change in x86 ld.so checks it and my test verifies the check. My fix
> won't cover other possible IFUNC failures.
>
When the IFUNC relocation is performed before the providing shared
library is unrelocated, the returned function address will be 0 and
program will segfault when the function is called.
Please apply this patch and run the test if your platform has IFUNC. I only
enabled the unsafe resolver check for i386 and x86-64. It is straightforward
to add check for other platforms.
H.J.
Comments
On 1/13/17 11:03 AM, H.J. Lu wrote:
> On Wed, Oct 12, 2016 at 3:19 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Tue, Oct 11, 2016 at 10:45 PM, Carlos O'Donell <carlos@redhat.com> wrote:
>>> On 10/05/2016 02:16 PM, H.J. Lu wrote:
>>>> On Tue, Oct 4, 2016 at 5:09 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>>>>> On Wed, 5 Oct 2016, H.J. Lu wrote:
>>>>>
>>>>>> I can try __builtin_memcpy, instread of __builtin_memmove. There are 2
>>>>
>>>> I changed it to use __builtin_memset.
>>>>
>>>>>> acceptable results. One is ld.so issues an error and the other is program runs.
>>>>>> On x86, ld.so issues an error. I don't know what should happen on others.
>>>>>
>>>>> You could make the test pass on either of those results (while failing if
>>>>> ld.so crashes).
>>>>>
>>>>
>>>> I moved the test to elf. It passes if the test runs or ld.so issues an
>>>> error. Please try it on arm, powerpc and s390.
>>>
>>> This is the wrong way to test this.
>>>
>>> The point of this test is this:
>>>
>>> - Verify that an unversioned symbol reference in DSO A which has no DT_NEEDED
>>> on DSO B, when resolved to a symbol definition in DSO B, when the symbol in
>>> DSO B is an IFUNC with a resolver, that DSO B is relocated _before_ the IFUNC
>>> resolver is called, because DSO B's resolver might need global data to make
>>> the IFUNC decision e.g. GOT setup.
>>>
>>> The invariant we want to hold true for IFUNC is that to call the resolver
>>> function you must have relocated the DSO which contains the resolver. This _should_
>>> have been done by a symbol reocation dependency analysis, but that isn't working
>>> correctly IMO or needs deeper analysis in the dynamic loader.
>>>
>>> The solution we want in place today is to issue some kind of diagnostic until we
>>> fix the real problem.
>>>
>>> The test should look like this:
>>>
>>> - DSO A with an unversioned symbol reference to 'foo'.
>>> - DSO B with a symbol definition of 'foo' as an ifunc with 'foo_resolver' as the
>>> resolver function which references global data from DSO C to decide which of
>>> two functions to return.
>>> - DSO C with global data set to a value.
>>>
>>> The point is that DSO B depends on DSO C and has DT_NEEDED on it, so C will get
>>> relocated first, then B, such that B's GOT is setup to access C's global data.
>>>
>>> When handling the reference to 'foo' in DSO A we should on x86_64 and i686
>>> get the error about needing to relink DSO A so it depends on DSO B, to form
>>> the initialization order of C->B->A.
>>>
>>> I expect this test case will now crash the other arches, rather than just
>>> avoiding the crash by relying on internal libc.so details about which ifuncs
>>> you're using.
>>>
>>> This is one step towards a better definition of IFUNC semantics, which need to
>>> be more clearly defined (something I wish I had time to define and fix so
>>> more projects could use them).
>>
>> IFUNC resolver can fail for various reasons. My goal is to make sure
>> that IFUNC inside of glibc works correctly or an error message is given
>> when glibc isn't used properly. In case of x86, CPU feature info is
>> retrieved and stored in ld.so very early at startup, which is used by IFUNC
>> and only accessible in libc.so and libm.so after they have been relocated.
>> My change in x86 ld.so checks it and my test verifies the check. My fix
>> won't cover other possible IFUNC failures.
>>
>
> When the IFUNC relocation is performed before the providing shared
> library is unrelocated, the returned function address will be 0 and
> program will segfault when the function is called.
>
> Please apply this patch and run the test if your platform has IFUNC. I only
> enabled the unsafe resolver check for i386 and x86-64. It is straightforward
> to add check for other platforms.
I will test it out shortly. One thing I see, the runner script for test
is calling out for /bin/bash and the script does not use any bash
extentions perhaps using /bin/sh is enough.
>
>
> H.J.
>
From 5db1cdaef209ba5b742308d5dcb299aaacdf3f92 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Thu, 12 Jan 2017 15:27:05 -0800
Subject: [PATCH] Add an IFUNC testcase for [BZ #20019]
When the IFUNC relocation is performed before the providing shared
library is unrelocated, the returned function address will be 0 and
program will segfault when the function is called. Add a testcase
to verify that ld.so issues a diagnostic.
[BZ #20019]
* elf/Makefile (modules-names): Add tst-ifuncmod1a,
tst-ifuncmod1b, tst-ifuncmod1c and tst-ifuncmod1d.
(tests): Add tst-ifunc1.
(tests-special): Add $(objpfx)tst-ifunc1.out.
($(objpfx)tst-ifunc1.out): New rule.
($(objpfx)tst-ifunc1): New dependency.
($(objpfx)tst-ifuncmod1a.so): LIkewise.
($(objpfx)tst-ifuncmod1b.so): LIkewise.
($(objpfx)tst-ifuncmod1c.so): LIkewise.
(LDFLAGS-tst-ifuncmod1b.so): New.
* elf/tst-ifunc1.c: New file.
* elf/tst-ifunc1.sh: LIkewise.
* elf/tst-ifuncmod1a.c: LIkewise.
* elf/tst-ifuncmod1b.c: LIkewise.
* elf/tst-ifuncmod1c.c: LIkewise.
* elf/tst-ifuncmod1d.c: LIkewise.
* sysdeps/generic/ldsodefs.h (dl_check_ifunc_resolver): New
function.
* sysdeps/i386/dl-machine.h (elf_machine_rel): Use it.
* sysdeps/x86_64/dl-machine.h (elf_machine_rela): LIkewise.
---
elf/Makefile | 19 +++++++++++++++++--
elf/tst-ifunc1.c | 26 ++++++++++++++++++++++++++
elf/tst-ifunc1.sh | 43 +++++++++++++++++++++++++++++++++++++++++++
elf/tst-ifuncmod1a.c | 25 +++++++++++++++++++++++++
elf/tst-ifuncmod1b.c | 25 +++++++++++++++++++++++++
elf/tst-ifuncmod1c.c | 27 +++++++++++++++++++++++++++
elf/tst-ifuncmod1d.c | 24 ++++++++++++++++++++++++
sysdeps/generic/ldsodefs.h | 26 ++++++++++++++++++++++++++
sysdeps/i386/dl-machine.h | 13 +------------
sysdeps/x86_64/dl-machine.h | 13 +------------
10 files changed, 215 insertions(+), 26 deletions(-)
create mode 100644 elf/tst-ifunc1.c
create mode 100755 elf/tst-ifunc1.sh
create mode 100644 elf/tst-ifuncmod1a.c
create mode 100644 elf/tst-ifuncmod1b.c
create mode 100644 elf/tst-ifuncmod1c.c
create mode 100644 elf/tst-ifuncmod1d.c
@@ -307,9 +307,11 @@ tests += ifuncmain1 ifuncmain1pic ifuncmain1vis ifuncmain1vispic \
ifuncmain1staticpic \
ifuncmain2 ifuncmain2pic ifuncmain3 ifuncmain4 \
ifuncmain5 ifuncmain5pic ifuncmain5staticpic \
- ifuncmain7 ifuncmain7pic
+ ifuncmain7 ifuncmain7pic tst-ifunc1
+tests-special += $(objpfx)tst-ifunc1.out
ifunc-test-modules = ifuncdep1 ifuncdep1pic ifuncdep2 ifuncdep2pic \
- ifuncdep5 ifuncdep5pic
+ ifuncdep5 ifuncdep5pic tst-ifuncmod1a \
+ tst-ifuncmod1b tst-ifuncmod1c tst-ifuncmod1d
extra-test-objs += $(ifunc-test-modules:=.o)
test-extras += $(ifunc-test-modules)
ifeq (yes,$(have-fpie))
@@ -1026,6 +1028,19 @@ CFLAGS-tst-pie2.c += $(pie-ccflag)
$(objpfx)tst-piemod1.so: $(libsupport)
$(objpfx)tst-pie1: $(objpfx)tst-piemod1.so
+$(objpfx)tst-ifunc1.out: tst-ifunc1.sh $(objpfx)tst-ifunc1
+ $(BASH) $< $(objpfx) '$(test-via-rtld-prefix)' \
+ '$(test-wrapper-env)' '$(run-program-env)'; \
+ $(evaluate-test)
+
+$(objpfx)tst-ifunc1: $(objpfx)tst-ifuncmod1a.so \
+ $(objpfx)tst-ifuncmod1c.so \
+ $(objpfx)tst-ifuncmod1d.so
+$(objpfx)tst-ifuncmod1a.so: $(objpfx)tst-ifuncmod1b.so
+$(objpfx)tst-ifuncmod1b.so: $(objpfx)tst-ifuncmod1d.so
+$(objpfx)tst-ifuncmod1c.so: $(objpfx)tst-ifuncmod1d.so
+LDFLAGS-tst-ifuncmod1b.so = -Wl,-z,now
+
ifeq (yes,$(build-shared))
all-built-dso := $(common-objpfx)elf/ld.so $(common-objpfx)libc.so \
$(filter-out $(common-objpfx)linkobj/libc.so, \
new file mode 100644
@@ -0,0 +1,26 @@
+/* Test case for unsafe IFUNC resolver.
+ 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/>. */
+
+extern void foo (void);
+
+int
+main (void)
+{
+ foo ();
+ return 0;
+}
new file mode 100755
@@ -0,0 +1,43 @@
+#!/bin/bash
+# A Test case for unsafe IFUNC resolver.
+# 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/>.
+
+set -e
+
+objpfx=$1; shift
+test_via_rtld_prefix=$1; shift
+test_wrapper_env=$1; shift
+run_program_env=$1; shift
+logfile=${objpfx}tst-ifunc1.out
+
+> $logfile
+fail=0
+
+${test_wrapper_env} \
+${run_program_env} \
+${objpfx}tst-ifunc1 2>&1 || fail=1
+
+if test $fail = 1; then
+ # If it fails to run, check for the expected error from ld.so.
+ fail=0
+ ${test_wrapper_env} \
+ ${run_program_env} \
+ ${objpfx}tst-ifunc1 2>&1 | grep Relink >> $logfile || fail=1
+fi
+
+exit $fail
new file mode 100644
@@ -0,0 +1,25 @@
+/* Test case for unsafe IFUNC resolver.
+ 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/>. */
+
+extern void bar (void);
+
+void
+foo (void)
+{
+ bar ();
+}
new file mode 100644
@@ -0,0 +1,25 @@
+/* Test case for unsafe IFUNC resolver.
+ 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/>. */
+
+extern void xxx (void);
+
+void
+bar (void)
+{
+ xxx ();
+}
new file mode 100644
@@ -0,0 +1,27 @@
+/* Test case for unsafe IFUNC resolver.
+ 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/>. */
+
+extern void real_xxx (void);
+
+static void *
+xxx_resolver (void)
+{
+ return &real_xxx;
+}
+
+extern void xxx (void) __attribute__ ((ifunc ("xxx_resolver")));
new file mode 100644
@@ -0,0 +1,24 @@
+/* Test case for unsafe IFUNC resolver.
+ 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/>. */
+
+void
+xxx (void)
+{
+}
+
+__typeof (xxx) real_xxx __attribute__ ((alias("xxx")));
@@ -1085,6 +1085,32 @@ extern void _dl_non_dynamic_init (void) internal_function;
extern void _dl_aux_init (ElfW(auxv_t) *av) internal_function;
+# ifdef STDERR_FILENO
+/* Define here after RTLD_PROGNAME is defined and if STDERR_FILENO is
+ defined. Since it is unsafe for IFUNC resolver to reference external
+ symbols, issue a fatal error when it happens. */
+static __always_inline void
+dl_check_ifunc_resolver (struct link_map *sym_map, struct link_map *map,
+ const ElfW(Sym) *const refsym)
+{
+ if (sym_map != map
+ && sym_map->l_type != lt_executable
+ && !sym_map->l_relocated)
+ {
+ const char *strtab
+ = (const char *) D_PTR (map, l_info[DT_STRTAB]);
+ _dl_fatal_printf ("\
+%s: Relink `%s' with `%s' or place `%s' before `%s' for IFUNC symbol `%s'\n",
+ RTLD_PROGNAME,
+ map->l_libname->name,
+ sym_map->l_libname->name,
+ sym_map->l_libname->name,
+ map->l_libname->name,
+ strtab + refsym->st_name);
+ }
+}
+# endif
+
__END_DECLS
#endif /* ldsodefs.h */
@@ -323,18 +323,7 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
&& __builtin_expect (!skip_ifunc, 1))
{
# ifndef RTLD_BOOTSTRAP
- if (sym_map != map
- && sym_map->l_type != lt_executable
- && !sym_map->l_relocated)
- {
- const char *strtab
- = (const char *) D_PTR (map, l_info[DT_STRTAB]);
- _dl_fatal_printf ("\
-%s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
- RTLD_PROGNAME, map->l_name,
- sym_map->l_name,
- strtab + refsym->st_name);
- }
+ dl_check_ifunc_resolver (sym_map, map, refsym);
# endif
value = ((Elf32_Addr (*) (void)) value) ();
}
@@ -333,18 +333,7 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
&& __builtin_expect (!skip_ifunc, 1))
{
# ifndef RTLD_BOOTSTRAP
- if (sym_map != map
- && sym_map->l_type != lt_executable
- && !sym_map->l_relocated)
- {
- const char *strtab
- = (const char *) D_PTR (map, l_info[DT_STRTAB]);
- _dl_fatal_printf ("\
-%s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
- RTLD_PROGNAME, map->l_name,
- sym_map->l_name,
- strtab + refsym->st_name);
- }
+ dl_check_ifunc_resolver (sym_map, map, refsym);
# endif
value = ((ElfW(Addr) (*) (void)) value) ();
}
--
2.9.3