From f33632ccd1dec3217583fcfdd965afb62954203c Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Thu, 30 Nov 2017 04:49:25 -0800 Subject: x86: Make a space in jmpbuf for shadow stack pointer To support Shadow Stack (SHSTK) in Intel Control-flow Enforcement Technology (CET) in setjmp/longjmp, we need to save shadow stack pointer in jmp_buf. The __saved_mask field in jmp_buf has type of __sigset_t. On Linux, __sigset_t is defined as #define _SIGSET_NWORDS (1024 / (8 * sizeof (unsigned long int))) typedef struct { unsigned long int __val[_SIGSET_NWORDS]; } __sigset_t; which is much bigger than expected by the __sigprocmask system call, which has typedef struct { unsigned long sig[_NSIG_WORDS]; } sigset_t; For Linux/x86, we can shrink __sigset_t used by __saved_mask in jmp_buf to add paddings for shadow stack pointer. As long as the new __sigset_t is not smaller than sigset_t expected by the __sigprocmask system call, it should work correctly. This patch adds an internal header file, , to define __jmp_buf_sigset_t for __saved_mask in jmp_buf for Linux/x86 with a space to store shadow stack pointer. It verifies __jmp_buf_sigset_t has the suitable size for the __sigprocmask system call. A run-time test, tst-saved_mask-1.c, is added to verify that size of __jmp_buf_sigset_t is sufficient. If its size is too small, the test fails with rt_sigprocmask(SIG_SETMASK, strace: umoven: short read (4 < 8) @0x7fa8aa28effc 0x7fa8aa28effc, NULL, 8) = -1 EFAULT (Bad address) rt_sigprocmask(SIG_SETMASK, strace: umoven: short read (4 < 8) @0x7fa8aa28effc 0x7fa8aa28effc, NULL, 8) = -1 EFAULT (Bad address) rt_sigprocmask(SIG_SETMASK, NULL, 0x7fa8aa28effc, 8) = -1 EFAULT (Bad address) exit_group(1) = ? Tested with build-many-glibcs.py. * debug/longjmp_chk.c: Include instead of . * setjmp/longjmp.c: Include instead of . (__libc_siglongjmp): Cast &env[0].__saved_mask to "sigset_t *". * setjmp/sigjmp.c: Include instead of . (__sigjmp_save): Cast &env[0].__saved_mask to "sigset_t *". * sysdeps/generic/setjmpP.h: New file. * sysdeps/unix/sysv/linux/x86/jmp_buf-ssp.sym: Likewise. * sysdeps/unix/sysv/linux/x86/setjmpP.h: Likewise. * sysdeps/unix/sysv/linux/x86/tst-saved_mask-1.c: Likewise. * sysdeps/unix/sysv/linux/x86/Makefile (gen-as-const-headers): Add jmp_buf-ssp.sym. (tests): Add tst-saved_mask-1. --- setjmp/longjmp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'setjmp/longjmp.c') diff --git a/setjmp/longjmp.c b/setjmp/longjmp.c index 2453c2c124..e144a874d7 100644 --- a/setjmp/longjmp.c +++ b/setjmp/longjmp.c @@ -16,7 +16,7 @@ . */ #include -#include +#include #include @@ -31,7 +31,8 @@ __libc_siglongjmp (sigjmp_buf env, int val) if (env[0].__mask_was_saved) /* Restore the saved signal mask. */ - (void) __sigprocmask (SIG_SETMASK, &env[0].__saved_mask, + (void) __sigprocmask (SIG_SETMASK, + (sigset_t *) &env[0].__saved_mask, (sigset_t *) NULL); /* Call the machine-dependent function to restore machine state. */ -- cgit 1.4.1