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x86/CET: Update vfork to prevent child return
Child of vfork should either call _exit or one of the exec family of functions. But normally there is nothing to prevent child of vfork from return of the vfork-calling function. Simpilfy x86 vfork when shadow stack is in use to introduce mismatched shadow stack in child of vfork to trigger SIGSEGV when the child returns from the function in which vfork was called.
This commit is contained in:
H.J. Lu
parent
b8b53b338f
commit
c02695d776
@ -21,39 +21,6 @@
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#include <bits/errno.h>
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#include <tcb-offsets.h>
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#if SHSTK_ENABLED
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/* The shadow stack prevents us from pushing the saved return PC onto
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the stack and returning normally. Instead we pop the shadow stack
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and return directly. This is the safest way to return and ensures
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any stack manipulations done by the vfork'd child doesn't cause the
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parent to terminate when CET is enabled. */
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# undef SYSCALL_ERROR_HANDLER
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# ifdef PIC
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# define SYSCALL_ERROR_HANDLER \
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0: \
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calll .L1; \
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.L1: \
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popl %edx; \
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.L2: \
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addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \
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movl __libc_errno@gotntpoff(%edx), %edx; \
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negl %eax; \
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movl %eax, %gs:(%edx); \
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orl $-1, %eax; \
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jmp 1b;
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# else
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# define SYSCALL_ERROR_HANDLER \
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0: \
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movl __libc_errno@indntpoff, %edx; \
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negl %eax; \
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movl %eax, %gs:(%edx); \
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orl $-1, %eax; \
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jmp 1b;
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# endif
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# undef SYSCALL_ERROR_LABEL
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# define SYSCALL_ERROR_LABEL 0f
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#endif
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/* Clone the calling process, but without copying the whole address space.
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The calling process is suspended until the new process exits or is
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replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
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@ -70,20 +37,17 @@ ENTRY (__vfork)
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movl $SYS_ify (vfork), %eax
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int $0x80
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#if !SHSTK_ENABLED
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/* Jump to the return PC. Don't jump directly since this
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disturbs the branch target cache. Instead push the return
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address back on the stack. */
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pushl %ecx
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cfi_adjust_cfa_offset (4)
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#endif
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cmpl $-4095, %eax
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/* Branch forward if it failed. */
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jae SYSCALL_ERROR_LABEL
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#if SHSTK_ENABLED
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1:
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/* Check if shadow stack is in use. */
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xorl %edx, %edx
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rdsspd %edx
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@ -91,18 +55,19 @@ ENTRY (__vfork)
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/* Normal return if shadow stack isn't in use. */
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je L(no_shstk)
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/* Pop return address from shadow stack and jump back to caller
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directly. */
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movl $1, %edx
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incsspd %edx
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testl %eax, %eax
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/* In parent, normal return. */
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jnz L(no_shstk)
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/* NB: In child, jump back to caller via indirect branch without
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popping shadow stack which is shared with parent. Keep shadow
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stack mismatched so that child returns in the vfork-calling
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function will trigger SIGSEGV. */
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popl %ecx
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cfi_adjust_cfa_offset (-4)
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jmp *%ecx
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L(no_shstk):
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/* Jump to the return PC. Don't jump directly since this
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disturbs the branch target cache. Instead push the return
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address back on the stack. */
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pushl %ecx
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cfi_adjust_cfa_offset (4)
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#endif
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ret
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@ -40,6 +40,11 @@ $(objpfx)tst-cet-property-2.out: $(objpfx)tst-cet-property-2 \
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$(evaluate-test)
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endif
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ifeq ($(subdir),posix)
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tests += tst-cet-vfork-1
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CFLAGS-tst-cet-vfork-1.c += -mshstk
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endif
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ifeq ($(subdir),stdlib)
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tests += tst-cet-setcontext-1
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CFLAGS-tst-cet-setcontext-1.c += -mshstk
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88
sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c
Normal file
88
sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c
Normal file
@ -0,0 +1,88 @@
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/* Verify that child of the vfork-calling function can't return when
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shadow stack is in use.
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Copyright (C) 2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <x86intrin.h>
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#include <support/test-driver.h>
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#include <support/xsignal.h>
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#include <support/xunistd.h>
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__attribute__ ((noclone, noinline))
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static void
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do_test_1 (void)
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{
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pid_t p1;
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int fd[2];
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if (pipe (fd) == -1)
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{
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puts ("pipe failed");
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_exit (EXIT_FAILURE);
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}
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if ((p1 = vfork ()) == 0)
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{
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pid_t p = getpid ();
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TEMP_FAILURE_RETRY (write (fd[1], &p, sizeof (p)));
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/* Child return should trigger SIGSEGV. */
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return;
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}
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else if (p1 == -1)
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{
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puts ("vfork failed");
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_exit (EXIT_FAILURE);
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}
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pid_t p2 = 0;
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if (TEMP_FAILURE_RETRY (read (fd[0], &p2, sizeof (pid_t)))
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!= sizeof (pid_t))
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puts ("pipd read failed");
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else
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{
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int r;
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if (TEMP_FAILURE_RETRY (waitpid (p1, &r, 0)) != p1)
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puts ("waitpid failed");
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else if (r != 0)
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puts ("pip write in child failed");
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}
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/* Parent exits immediately so that parent returns without triggering
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SIGSEGV when shadow stack isn't in use. */
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_exit (EXIT_FAILURE);
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}
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static int
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do_test (void)
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{
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/* NB: This test should trigger SIGSEGV with shadow stack enabled. */
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if (_get_ssp () == 0)
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return EXIT_UNSUPPORTED;
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do_test_1 ();
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/* Child exits immediately so that child returns without triggering
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SIGSEGV when shadow stack isn't in use. */
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_exit (EXIT_FAILURE);
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}
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#define EXPECTED_SIGNAL (_get_ssp () == 0 ? 0 : SIGSEGV)
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#include <support/test-driver.c>
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@ -20,22 +20,6 @@
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#include <bits/errno.h>
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#include <tcb-offsets.h>
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#if SHSTK_ENABLED
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/* The shadow stack prevents us from pushing the saved return PC onto
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the stack and returning normally. Instead we pop the shadow stack
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and return directly. This is the safest way to return and ensures
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any stack manipulations done by the vfork'd child doesn't cause the
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parent to terminate when CET is enabled. */
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# undef SYSCALL_ERROR_HANDLER
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# define SYSCALL_ERROR_HANDLER \
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0: \
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SYSCALL_SET_ERRNO; \
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or $-1, %RAX_LP; \
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jmp 1b;
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# undef SYSCALL_ERROR_LABEL
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# define SYSCALL_ERROR_LABEL 0f
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#endif
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/* Clone the calling process, but without copying the whole address space.
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The calling process is suspended until the new process exits or is
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replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
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@ -53,17 +37,14 @@ ENTRY (__vfork)
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movl $SYS_ify (vfork), %eax
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syscall
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#if !SHSTK_ENABLED
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/* Push back the return PC. */
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pushq %rdi
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cfi_adjust_cfa_offset(8)
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#endif
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cmpl $-4095, %eax
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jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
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#if SHSTK_ENABLED
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1:
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/* Check if shadow stack is in use. */
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xorl %esi, %esi
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rdsspq %rsi
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@ -71,16 +52,19 @@ ENTRY (__vfork)
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/* Normal return if shadow stack isn't in use. */
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je L(no_shstk)
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/* Pop return address from shadow stack and jump back to caller
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directly. */
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movl $1, %esi
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incsspq %rsi
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testl %eax, %eax
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/* In parent, normal return. */
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jnz L(no_shstk)
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/* NB: In child, jump back to caller via indirect branch without
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popping shadow stack which is shared with parent. Keep shadow
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stack mismatched so that child returns in the vfork-calling
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function will trigger SIGSEGV. */
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popq %rdi
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cfi_adjust_cfa_offset(-8)
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jmp *%rdi
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L(no_shstk):
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/* Push back the return PC. */
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pushq %rdi
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cfi_adjust_cfa_offset(8)
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#endif
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/* Normal return. */
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