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| author | H.J. Lu <hjl.tools@gmail.com> | 2018-07-24 05:20:48 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2018-07-24 05:21:07 -0700 |
| commit | 3650e1d9284926be67e368707a9a2276fb77a167 (patch) | |
| tree | e278a6deadd6d347e1446104bbea53144045ba7a /sysdeps/unix/sysv/linux/i386 | |
| parent | ca027e0f62789a0958b69dac4133616a90de6f7c (diff) | |
| download | glibc-3650e1d9284926be67e368707a9a2276fb77a167.tar.gz glibc-3650e1d9284926be67e368707a9a2276fb77a167.tar.xz glibc-3650e1d9284926be67e368707a9a2276fb77a167.zip | |
x86: Update vfork to pop shadow stack
The shadow stack prevents us from pushing the saved return PC onto the stack and returning normally. Instead we pop the shadow stack and return directly. This is the safest way to return and ensures any stack manipulations done by the vfork'd child doesn't cause the parent to terminate when CET is enabled. Reviewed-by: Carlos O'Donell <carlos@redhat.com> * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use. * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use.
Diffstat (limited to 'sysdeps/unix/sysv/linux/i386')
| -rw-r--r-- | sysdeps/unix/sysv/linux/i386/vfork.S | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S index 8f40d02d09..ce6dbfac48 100644 --- a/sysdeps/unix/sysv/linux/i386/vfork.S +++ b/sysdeps/unix/sysv/linux/i386/vfork.S @@ -21,6 +21,38 @@ #include <bits/errno.h> #include <tcb-offsets.h> +#if SHSTK_ENABLED +/* The shadow stack prevents us from pushing the saved return PC onto + the stack and returning normally. Instead we pop the shadow stack + and return directly. This is the safest way to return and ensures + any stack manipulations done by the vfork'd child doesn't cause the + parent to terminate when CET is enabled. */ +# undef SYSCALL_ERROR_HANDLER +# ifdef PIC +# define SYSCALL_ERROR_HANDLER \ +0: \ + calll .L1; \ +.L1: \ + popl %edx; \ +.L2: \ + addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \ + movl __libc_errno@gotntpoff(%edx), %edx; \ + negl %eax; \ + movl %eax, %gs:(%edx); \ + orl $-1, %eax; \ + jmp 1b; +# else +# define SYSCALL_ERROR_HANDLER \ +0: \ + movl __libc_errno@indntpoff, %edx; \ + negl %eax; \ + movl %eax, %gs:(%edx); \ + orl $-1, %eax; \ + jmp 1b; +# endif +# undef SYSCALL_ERROR_LABEL +# define SYSCALL_ERROR_LABEL 0f +#endif /* Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is @@ -38,16 +70,41 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax int $0x80 +#if !SHSTK_ENABLED /* Jump to the return PC. Don't jump directly since this disturbs the branch target cache. Instead push the return address back on the stack. */ pushl %ecx cfi_adjust_cfa_offset (4) +#endif cmpl $-4095, %eax /* Branch forward if it failed. */ jae SYSCALL_ERROR_LABEL +#if SHSTK_ENABLED +1: + /* Check if shadow stack is in use. */ + xorl %edx, %edx + rdsspd %edx + testl %edx, %edx + /* Normal return if shadow stack isn't in use. */ + je L(no_shstk) + + /* Pop return address from shadow stack and jump back to caller + directly. */ + movl $1, %edx + incsspd %edx + jmp *%ecx + +L(no_shstk): + /* Jump to the return PC. Don't jump directly since this + disturbs the branch target cache. Instead push the return + address back on the stack. */ + pushl %ecx + cfi_adjust_cfa_offset (4) +#endif + ret PSEUDO_END (__vfork) |