diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/x86_64/vfork.S')
| -rw-r--r-- | sysdeps/unix/sysv/linux/x86_64/vfork.S | 36 |
1 files changed, 10 insertions, 26 deletions
diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S index 776d2fc610..613ff7e846 100644 --- a/sysdeps/unix/sysv/linux/x86_64/vfork.S +++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S @@ -20,22 +20,6 @@ #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 -# define SYSCALL_ERROR_HANDLER \ -0: \ - SYSCALL_SET_ERRNO; \ - or $-1, %RAX_LP; \ - jmp 1b; -# 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 replaced by a call to `execve'. Return -1 for errors, 0 to the new process, @@ -53,17 +37,14 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax syscall -#if !SHSTK_ENABLED /* Push back the return PC. */ pushq %rdi cfi_adjust_cfa_offset(8) -#endif cmpl $-4095, %eax jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */ #if SHSTK_ENABLED -1: /* Check if shadow stack is in use. */ xorl %esi, %esi rdsspq %rsi @@ -71,16 +52,19 @@ ENTRY (__vfork) /* 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, %esi - incsspq %rsi + testl %eax, %eax + /* In parent, normal return. */ + jnz L(no_shstk) + + /* NB: In child, jump back to caller via indirect branch without + popping shadow stack which is shared with parent. Keep shadow + stack mismatched so that child returns in the vfork-calling + function will trigger SIGSEGV. */ + popq %rdi + cfi_adjust_cfa_offset(-8) jmp *%rdi L(no_shstk): - /* Push back the return PC. */ - pushq %rdi - cfi_adjust_cfa_offset(8) #endif /* Normal return. */ |