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294 lines
8.6 KiB
294 lines
8.6 KiB
2 years ago
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commit c02695d776406faaf63418e4e80c4a7023af0b4f
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Author: H.J. Lu <hjl.tools@gmail.com>
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Date: Wed Sep 16 16:00:14 2020 -0700
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x86/CET: Update vfork to prevent child return
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Child of vfork should either call _exit or one of the exec family of
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functions. But normally there is nothing to prevent child of vfork from
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return of the vfork-calling function. Simpilfy x86 vfork when shadow
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stack is in use to introduce mismatched shadow stack in child of vfork
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to trigger SIGSEGV when the child returns from the function in which
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vfork was called.
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---
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diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S
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index ceb41db0bd..91277a639f 100644
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--- a/sysdeps/unix/sysv/linux/i386/vfork.S
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+++ b/sysdeps/unix/sysv/linux/i386/vfork.S
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@@ -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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-
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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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+
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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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diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile
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index 50fd018fa3..6bfd6bec49 100644
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--- a/sysdeps/unix/sysv/linux/x86/Makefile
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+++ b/sysdeps/unix/sysv/linux/x86/Makefile
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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 ($(subdir),posix)
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+tests += tst-cet-vfork-1
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+CFLAGS-tst-cet-vfork-1.c += -mshstk
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+endif
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+
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ifeq ($(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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diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c
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new file mode 100644
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index 0000000000..5b9fc8c170
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--- /dev/null
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+++ b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c
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@@ -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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S
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index 776d2fc610..613ff7e846 100644
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--- a/sysdeps/unix/sysv/linux/x86_64/vfork.S
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+++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S
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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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-
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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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+
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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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--
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2.26.2
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