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([2804:1b3:a7c0:113e:3285:93c4:1e1c:a48]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22c50eb4925sm107953815ad.117.2025.04.23.11.21.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Apr 2025 11:21:36 -0700 (PDT) From: Adhemerval Zanella To: libc-alpha@sourceware.org Cc: Luke Drummond , Sam James Subject: [PATCH] nptl: Fix pthread_getattr_np when modules with execstack are allowed (BZ 32897) Date: Wed, 23 Apr 2025 15:21:25 -0300 Message-ID: <20250423182133.2544501-1-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 X-Spam-Status: No, score=-12.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patchwork=sourceware.org@sourceware.org The BZ 32653 fix (12a497c716f0a06be5946cabb8c3ec22a079771e) kept the stack pointer zeroing from make_main_stack_executable on _dl_make_stack_executable. However, previously the 'stack_endp' pointed to temporary variable created before the call of _dl_map_object_from_fd; while now we use the __libc_stack_end directly. Since pthread_getattr_np relies on correct __libc_stack_end, if _dl_make_stack_executable s called after process startup (for instance, when glibc.rtld.execstack=2 is set and a module with an executable stack is loaded) __libc_stack_end will be set to zero, and the call will always fail. The __libc_stack_end zero was used a mitigation hardening, but since 52a01100ad011293197637e42b5be1a479a2f4ae it is used solely on pthread_getattr_np code. So there is no point in zeroing anymore. Checked on x86_64-linux-gnu and i686-linux-gnu. Reviewed-by: Sam James --- elf/dl-execstack-tunable.c | 2 +- elf/dl-execstack.c | 2 +- sysdeps/generic/ldsodefs.h | 2 +- sysdeps/mach/hurd/dl-execstack.c | 5 ++-- sysdeps/pthread/Makefile | 9 ++++++ sysdeps/pthread/tst-stack2-mod.c | 39 +++++++++++++++++++++++++ sysdeps/pthread/tst-stack2.c | 40 ++++++++++++++++++++++++++ sysdeps/unix/sysv/linux/dl-execstack.c | 7 ++--- 8 files changed, 95 insertions(+), 11 deletions(-) create mode 100644 sysdeps/pthread/tst-stack2-mod.c create mode 100644 sysdeps/pthread/tst-stack2.c diff --git a/elf/dl-execstack-tunable.c b/elf/dl-execstack-tunable.c index 6cef1a3036..e3b638aeaa 100644 --- a/elf/dl-execstack-tunable.c +++ b/elf/dl-execstack-tunable.c @@ -31,7 +31,7 @@ _dl_handle_execstack_tunable (void) break; case stack_tunable_mode_force: - if (_dl_make_stack_executable (&__libc_stack_end) != 0) + if (_dl_make_stack_executable (__libc_stack_end) != 0) _dl_fatal_printf ( "Fatal glibc error: cannot enable executable stack as tunable requires"); break; diff --git a/elf/dl-execstack.c b/elf/dl-execstack.c index e4d7dbe7f8..ceec5b2def 100644 --- a/elf/dl-execstack.c +++ b/elf/dl-execstack.c @@ -23,7 +23,7 @@ so as to mprotect it. */ int -_dl_make_stack_executable (void **stack_endp) +_dl_make_stack_executable (const void *stack_endp) { return ENOSYS; } diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index b5d5b3106c..fc4a3de767 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -733,7 +733,7 @@ void _dl_handle_execstack_tunable (void) attribute_hidden; /* This function changes the permission of the memory region pointed by STACK_ENDP to executable and update the internal memory protection flags for future thread stack creation. */ -int _dl_make_stack_executable (void **stack_endp) attribute_hidden; +int _dl_make_stack_executable (const void *stack_endp) attribute_hidden; /* Variable pointing to the end of the stack (or close to it). This value must be constant over the runtime of the application. Some programs diff --git a/sysdeps/mach/hurd/dl-execstack.c b/sysdeps/mach/hurd/dl-execstack.c index 0617d3a161..dc4719bd38 100644 --- a/sysdeps/mach/hurd/dl-execstack.c +++ b/sysdeps/mach/hurd/dl-execstack.c @@ -26,12 +26,11 @@ extern struct hurd_startup_data *_dl_hurd_data attribute_hidden; so as to mprotect it. */ int -_dl_make_stack_executable (void **stack_endp) +_dl_make_stack_executable (const void *stack_endp) { /* Challenge the caller. */ - if (__builtin_expect (*stack_endp != __libc_stack_end, 0)) + if (__glibc_unlikely (stack_endp != __libc_stack_end)) return EPERM; - *stack_endp = NULL; #if IS_IN (rtld) if (__mprotect ((void *)_dl_hurd_data->stack_base, _dl_hurd_data->stack_size, diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile index d4869c624b..5acf505a90 100644 --- a/sysdeps/pthread/Makefile +++ b/sysdeps/pthread/Makefile @@ -273,6 +273,7 @@ tests += \ tst-spin4 \ tst-spin5 \ tst-stack1 \ + tst-stack2 \ tst-stdio1 \ tst-stdio2 \ tst-thrd-detach \ @@ -368,6 +369,7 @@ modules-names += \ tst-atfork4mod \ tst-create1mod \ tst-fini1mod \ + tst-stack2-mod \ tst-tls4moda \ tst-tls4modb \ # modules-names @@ -541,4 +543,11 @@ LDFLAGS-tst-create1 = -Wl,-export-dynamic $(objpfx)tst-create1: $(shared-thread-library) $(objpfx)tst-create1.out: $(objpfx)tst-create1mod.so +$(objpfx)tst-stack2.out: $(objpfx)tst-stack2-mod.so +LDFLAGS-tst-stack2-mod.so = -Wl,-z,execstack +ifeq ($(have-no-error-execstack),yes) +LDFLAGS-tst-stack2-mod.so += -Wl,--no-error-execstack +endif +tst-stack2-ENV = GLIBC_TUNABLES=glibc.rtld.execstack=2 + endif diff --git a/sysdeps/pthread/tst-stack2-mod.c b/sysdeps/pthread/tst-stack2-mod.c new file mode 100644 index 0000000000..806fdbcd8d --- /dev/null +++ b/sysdeps/pthread/tst-stack2-mod.c @@ -0,0 +1,39 @@ +/* Check if pthread_getattr_np works within modules with non-exectuble + stacks (BZ 32897). + Copyright (C) 2025 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 + . */ + +#include + +bool init_result; + +void +__attribute__ ((constructor)) +init (void) +{ + pthread_t me = pthread_self (); + pthread_attr_t attr; + init_result = pthread_getattr_np (me, &attr) == 0; +} + +int +mod_func (void) +{ + pthread_t me = pthread_self (); + pthread_attr_t attr; + return pthread_getattr_np (me, &attr); +} diff --git a/sysdeps/pthread/tst-stack2.c b/sysdeps/pthread/tst-stack2.c new file mode 100644 index 0000000000..f800390167 --- /dev/null +++ b/sysdeps/pthread/tst-stack2.c @@ -0,0 +1,40 @@ +/* Check if pthread_getattr_np works within modules with non-exectuble + stacks (BZ 32897). + Copyright (C) 2025 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 + . */ + +#include +#include +#include + +static int +do_test (void) +{ + void *h = xdlopen ("tst-stack2-mod.so", RTLD_NOW); + + bool *init_result = xdlsym (h, "init_result"); + TEST_COMPARE (*init_result, true); + + int (*mod_func)(void) = xdlsym (h, "mod_func"); + TEST_COMPARE (mod_func (), 0); + + xdlclose (h); + + return 0; +} + +#include diff --git a/sysdeps/unix/sysv/linux/dl-execstack.c b/sysdeps/unix/sysv/linux/dl-execstack.c index 9791b339ca..6db9601656 100644 --- a/sysdeps/unix/sysv/linux/dl-execstack.c +++ b/sysdeps/unix/sysv/linux/dl-execstack.c @@ -19,10 +19,10 @@ #include int -_dl_make_stack_executable (void **stack_endp) +_dl_make_stack_executable (const void *stack_endp) { /* This gives us the highest/lowest page that needs to be changed. */ - uintptr_t page = ((uintptr_t) *stack_endp + uintptr_t page = ((uintptr_t) stack_endp & -(intptr_t) GLRO(dl_pagesize)); if (__mprotect ((void *) page, GLRO(dl_pagesize), @@ -35,9 +35,6 @@ _dl_make_stack_executable (void **stack_endp) ) != 0) return errno; - /* Clear the address. */ - *stack_endp = NULL; - /* Remember that we changed the permission. */ GL(dl_stack_flags) |= PF_X;