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309 lines
9.7 KiB
309 lines
9.7 KiB
4 years ago
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commit 68448be208ee06e76665918b37b0a57e3e00c8b4
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Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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Date: Fri Nov 17 16:04:29 2017 -0200
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i386: Fix i386 sigaction sa_restorer initialization (BZ#21269)
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This patch fixes the i386 sa_restorer field initialization for sigaction
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syscall for kernel with vDSO. As described in bug report, i386 Linux
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(and compat on x86_64) interprets SA_RESTORER clear with nonzero
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sa_restorer as a request for stack switching if the SS segment is 'funny'.
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This means that anything that tries to mix glibc's signal handling with
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segmentation (for instance through modify_ldt syscall) is randomly broken
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depending on what values lands in sa_restorer.
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The testcase added is based on Linux test tools/testing/selftests/x86/ldt_gdt.c,
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more specifically in do_multicpu_tests function. The main changes are:
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- C11 atomics instead of plain access.
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- Remove x86_64 support which simplifies the syscall handling and fallbacks.
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- Replicate only the test required to trigger the issue.
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Checked on i686-linux-gnu.
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[BZ #21269]
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* sysdeps/unix/sysv/linux/i386/Makefile (tests): Add tst-bz21269.
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* sysdeps/unix/sysv/linux/i386/sigaction.c (SET_SA_RESTORER): Clear
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sa_restorer for vDSO case.
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* sysdeps/unix/sysv/linux/i386/tst-bz21269.c: New file.
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(Adjusted for conflicted in sysdeps/unix/sysv/linux/i386/Makefile due
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different context around the addition of the new test.)
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diff --git a/sysdeps/unix/sysv/linux/i386/Makefile b/sysdeps/unix/sysv/linux/i386/Makefile
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index acc30219e8dc965f..78e2101682d8d996 100644
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--- a/sysdeps/unix/sysv/linux/i386/Makefile
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+++ b/sysdeps/unix/sysv/linux/i386/Makefile
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@@ -3,6 +3,9 @@ default-abi := 32
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ifeq ($(subdir),misc)
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sysdep_routines += ioperm iopl vm86 call_pselect6 call_fallocate
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+
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+tests += tst-bz21269
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+$(objpfx)tst-bz21269: $(shared-thread-library)
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endif
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ifeq ($(subdir),elf)
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diff --git a/sysdeps/unix/sysv/linux/i386/sigaction.c b/sysdeps/unix/sysv/linux/i386/sigaction.c
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index 414ef759a97363c4..f10e1363865c3d18 100644
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--- a/sysdeps/unix/sysv/linux/i386/sigaction.c
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+++ b/sysdeps/unix/sysv/linux/i386/sigaction.c
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@@ -44,7 +44,6 @@ extern void restore_rt (void) asm ("__restore_rt") attribute_hidden;
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#endif
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extern void restore (void) asm ("__restore") attribute_hidden;
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-
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/* If ACT is not NULL, change the action for SIG to *ACT.
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If OACT is not NULL, put the old action for SIG in *OACT. */
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int
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@@ -67,6 +66,8 @@ __libc_sigaction (int sig, const struct sigaction *act, struct sigaction *oact)
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kact.sa_restorer = ((act->sa_flags & SA_SIGINFO)
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? &restore_rt : &restore);
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}
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+ else
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+ kact.sa_restorer = NULL;
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}
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/* XXX The size argument hopefully will have to be changed to the
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diff --git a/sysdeps/unix/sysv/linux/i386/tst-bz21269.c b/sysdeps/unix/sysv/linux/i386/tst-bz21269.c
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new file mode 100644
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index 0000000000000000..353e36507dce92ea
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--- /dev/null
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+++ b/sysdeps/unix/sysv/linux/i386/tst-bz21269.c
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@@ -0,0 +1,233 @@
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+/* Test for i386 sigaction sa_restorer handling (BZ#21269)
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+ Copyright (C) 2017 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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+ <http://www.gnu.org/licenses/>. */
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+
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+/* This is based on Linux test tools/testing/selftests/x86/ldt_gdt.c,
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+ more specifically in do_multicpu_tests function. The main changes
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+ are:
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+
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+ - C11 atomics instead of plain access.
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+ - Remove x86_64 support which simplifies the syscall handling
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+ and fallbacks.
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+ - Replicate only the test required to trigger the issue for the
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+ BZ#21269. */
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+
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+#include <stdatomic.h>
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+
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+#include <asm/ldt.h>
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+#include <linux/futex.h>
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+
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+#include <setjmp.h>
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+#include <signal.h>
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+#include <errno.h>
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+#include <sys/syscall.h>
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+#include <sys/mman.h>
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+
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+#include <support/xunistd.h>
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+#include <support/check.h>
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+#include <support/xthread.h>
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+
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+static int
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+xset_thread_area (struct user_desc *u_info)
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+{
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+ long ret = syscall (SYS_set_thread_area, u_info);
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+ TEST_VERIFY_EXIT (ret == 0);
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+ return ret;
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+}
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+
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+static void
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+xmodify_ldt (int func, const void *ptr, unsigned long bytecount)
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+{
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+ TEST_VERIFY_EXIT (syscall (SYS_modify_ldt, 1, ptr, bytecount) == 0);
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+}
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+
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+static int
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+futex (int *uaddr, int futex_op, int val, void *timeout, int *uaddr2,
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+ int val3)
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+{
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+ return syscall (SYS_futex, uaddr, futex_op, val, timeout, uaddr2, val3);
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+}
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+
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+static void
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+xsethandler (int sig, void (*handler)(int, siginfo_t *, void *), int flags)
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+{
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+ struct sigaction sa = { 0 };
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+ sa.sa_sigaction = handler;
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+ sa.sa_flags = SA_SIGINFO | flags;
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+ TEST_VERIFY_EXIT (sigemptyset (&sa.sa_mask) == 0);
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+ TEST_VERIFY_EXIT (sigaction (sig, &sa, 0) == 0);
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+}
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+
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+static jmp_buf jmpbuf;
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+
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+static void
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+sigsegv_handler (int sig, siginfo_t *info, void *ctx_void)
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+{
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+ siglongjmp (jmpbuf, 1);
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+}
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+
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+/* Points to an array of 1024 ints, each holding its own index. */
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+static const unsigned int *counter_page;
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+static struct user_desc *low_user_desc;
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+static struct user_desc *low_user_desc_clear; /* Used to delete GDT entry. */
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+static int gdt_entry_num;
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+
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+static void
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+setup_counter_page (void)
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+{
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+ long page_size = sysconf (_SC_PAGE_SIZE);
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+ TEST_VERIFY_EXIT (page_size > 0);
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+ unsigned int *page = xmmap (NULL, page_size, PROT_READ | PROT_WRITE,
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+ MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1);
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+ for (int i = 0; i < (page_size / sizeof (unsigned int)); i++)
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+ page[i] = i;
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+ counter_page = page;
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+}
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+
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+static void
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+setup_low_user_desc (void)
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+{
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+ low_user_desc = xmmap (NULL, 2 * sizeof (struct user_desc),
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+ PROT_READ | PROT_WRITE,
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+ MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1);
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+
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+ low_user_desc->entry_number = -1;
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+ low_user_desc->base_addr = (unsigned long) &counter_page[1];
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+ low_user_desc->limit = 0xffff;
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+ low_user_desc->seg_32bit = 1;
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+ low_user_desc->contents = 0;
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+ low_user_desc->read_exec_only = 0;
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+ low_user_desc->limit_in_pages = 1;
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+ low_user_desc->seg_not_present = 0;
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+ low_user_desc->useable = 0;
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+
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+ xset_thread_area (low_user_desc);
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+
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+ low_user_desc_clear = low_user_desc + 1;
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+ low_user_desc_clear->entry_number = gdt_entry_num;
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+ low_user_desc_clear->read_exec_only = 1;
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+ low_user_desc_clear->seg_not_present = 1;
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+}
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+
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+/* Possible values of futex:
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+ 0: thread is idle.
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+ 1: thread armed.
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+ 2: thread should clear LDT entry 0.
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+ 3: thread should exit. */
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+static atomic_uint ftx;
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+
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+static void *
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+threadproc (void *ctx)
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+{
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+ while (1)
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+ {
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+ futex ((int *) &ftx, FUTEX_WAIT, 1, NULL, NULL, 0);
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+ while (atomic_load (&ftx) != 2)
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+ {
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+ if (atomic_load (&ftx) >= 3)
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+ return NULL;
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+ }
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+
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+ /* clear LDT entry 0. */
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+ const struct user_desc desc = { 0 };
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+ xmodify_ldt (1, &desc, sizeof (desc));
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+
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+ /* If ftx == 2, set it to zero, If ftx == 100, quit. */
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+ if (atomic_fetch_add (&ftx, -2) != 2)
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+ return NULL;
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+ }
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+}
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+
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+
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+/* As described in testcase, for historical reasons x86_32 Linux (and compat
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+ on x86_64) interprets SA_RESTORER clear with nonzero sa_restorer as a
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+ request for stack switching if the SS segment is 'funny' (this is default
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+ scenario for vDSO system). This means that anything that tries to mix
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+ signal handling with segmentation should explicit clear the sa_restorer.
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+
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+ This testcase check if sigaction in fact does it by changing the local
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+ descriptor table (LDT) through the modify_ldt syscall and triggering
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+ a synchronous segfault on iret fault by trying to install an invalid
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+ segment. With a correct zeroed sa_restorer it should not trigger an
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+ 'real' SEGSEGV and allows the siglongjmp in signal handler. */
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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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+ setup_counter_page ();
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+ setup_low_user_desc ();
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+
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+ pthread_t thread;
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+ unsigned short orig_ss;
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+
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+ xsethandler (SIGSEGV, sigsegv_handler, 0);
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+ /* 32-bit kernels send SIGILL instead of SIGSEGV on IRET faults. */
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+ xsethandler (SIGILL, sigsegv_handler, 0);
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+
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+ thread = xpthread_create (0, threadproc, 0);
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+
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+ asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
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+
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+ for (int i = 0; i < 5; i++)
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+ {
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+ if (sigsetjmp (jmpbuf, 1) != 0)
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+ continue;
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+
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+ /* Make sure the thread is ready after the last test. */
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+ while (atomic_load (&ftx) != 0)
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+ ;
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+
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+ struct user_desc desc = {
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+ .entry_number = 0,
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+ .base_addr = 0,
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+ .limit = 0xffff,
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+ .seg_32bit = 1,
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+ .contents = 0,
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+ .read_exec_only = 0,
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+ .limit_in_pages = 1,
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+ .seg_not_present = 0,
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+ .useable = 0
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+ };
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+
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+ xmodify_ldt (0x11, &desc, sizeof (desc));
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+
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+ /* Arm the thread. */
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+ ftx = 1;
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+ futex ((int*) &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
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+
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+ asm volatile ("mov %0, %%ss" : : "r" (0x7));
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+
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+ /* Fire up thread modify_ldt call. */
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+ atomic_store (&ftx, 2);
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+
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+ while (atomic_load (&ftx) != 0)
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+ ;
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+
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+ /* On success, modify_ldt will segfault us synchronously and we will
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+ escape via siglongjmp. */
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+ support_record_failure ();
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+ }
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+
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+ atomic_store (&ftx, 100);
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+ futex ((int*) &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
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+
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+ xpthread_join (thread);
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+
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+ return 0;
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+}
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+
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+#include <support/test-driver.c>
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