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author | H.J. Lu <hjl.tools@gmail.com> | 2018-05-02 06:17:20 -0700 |
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committer | H.J. Lu <hjl.tools@gmail.com> | 2018-05-02 06:17:41 -0700 |
commit | d6cc1829aa31b6fb060f24dffd28aa6705cdd33a (patch) | |
tree | 197e7983f66d43765505f94a5a29d254d27f6d02 /nptl | |
parent | b109fbfe4dd2ca77656157ddaded773e0da630a2 (diff) | |
download | glibc-d6cc1829aa31b6fb060f24dffd28aa6705cdd33a.tar.gz glibc-d6cc1829aa31b6fb060f24dffd28aa6705cdd33a.tar.xz glibc-d6cc1829aa31b6fb060f24dffd28aa6705cdd33a.zip |
x86: Use pad in pthread_unwind_buf to preserve shadow stack register
The pad array in struct pthread_unwind_buf is used by setjmp to save shadow stack register. We assert that size of struct pthread_unwind_buf is no less than offset of shadow stack pointer + shadow stack pointer size. Since functions, like LIBC_START_MAIN, START_THREAD_DEFN as well as these with thread cancellation, call setjmp, but never return after __libc_unwind_longjmp, __libc_unwind_longjmp, which is defined as __libc_longjmp on x86, doesn't need to restore shadow stack register. __libc_longjmp, which is a private interface for thread cancellation implementation in libpthread, is changed to call __longjmp_cancel, instead of __longjmp. __longjmp_cancel is a new internal function in libc, which is similar to __longjmp, but doesn't restore shadow stack register. The compatibility longjmp and siglongjmp in libpthread.so are changed to call __libc_siglongjmp, instead of __libc_longjmp, so that they will restore shadow stack register. Tested with build-many-glibcs.py. Signed-off-by: H.J. Lu <hjl.tools@gmail.com> Reviewed-by: Carlos O'Donell <carlos@redhat.com> * nptl/pthread_create.c (START_THREAD_DEFN): Clear previous handlers after setjmp. * setjmp/longjmp.c (__libc_longjmp): Don't define alias if defined. * sysdeps/unix/sysv/linux/x86/setjmpP.h: Include <libc-pointer-arith.h>. (_JUMP_BUF_SIGSET_BITS_PER_WORD): New. (_JUMP_BUF_SIGSET_NSIG): Changed to 96. (_JUMP_BUF_SIGSET_NWORDS): Changed to use ALIGN_UP and _JUMP_BUF_SIGSET_BITS_PER_WORD. * sysdeps/x86/Makefile (sysdep_routines): Add __longjmp_cancel. * sysdeps/x86/__longjmp_cancel.S: New file. * sysdeps/x86/longjmp.c: Likewise. * sysdeps/x86/nptl/pt-longjmp.c: Likewise.
Diffstat (limited to 'nptl')
-rw-r--r-- | nptl/pthread_create.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c index caaf07c134..92c945b12b 100644 --- a/nptl/pthread_create.c +++ b/nptl/pthread_create.c @@ -427,12 +427,23 @@ START_THREAD_DEFN compilers without that support we do use setjmp. */ struct pthread_unwind_buf unwind_buf; - /* No previous handlers. */ + int not_first_call; + not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf); + + /* No previous handlers. NB: This must be done after setjmp since the + private space in the unwind jump buffer may overlap space used by + setjmp to store extra architecture-specific information which is + never used by the cancellation-specific __libc_unwind_longjmp. + + The private space is allowed to overlap because the unwinder never + has to return through any of the jumped-to call frames, and thus + only a minimum amount of saved data need be stored, and for example, + need not include the process signal mask information. This is all + an optimization to reduce stack usage when pushing cancellation + handlers. */ unwind_buf.priv.data.prev = NULL; unwind_buf.priv.data.cleanup = NULL; - int not_first_call; - not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf); if (__glibc_likely (! not_first_call)) { /* Store the new cleanup handler info. */ |