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i386: Fix i386 sigaction sa_restorer initialization (BZ#21269)
This patch fixes the i386 sa_restorer field initialization for sigaction syscall for kernel with vDSO. As described in bug report, i386 Linux (and compat on x86_64) interprets SA_RESTORER clear with nonzero sa_restorer as a request for stack switching if the SS segment is 'funny'. This means that anything that tries to mix glibc's signal handling with segmentation (for instance through modify_ldt syscall) is randomly broken depending on what values lands in sa_restorer. The testcase added is based on Linux test tools/testing/selftests/x86/ldt_gdt.c, more specifically in do_multicpu_tests function. The main changes are: - C11 atomics instead of plain access. - Remove x86_64 support which simplifies the syscall handling and fallbacks. - Replicate only the test required to trigger the issue. Checked on i686-linux-gnu. [BZ #21269] * sysdeps/unix/sysv/linux/i386/Makefile (tests): Add tst-bz21269. * sysdeps/unix/sysv/linux/i386/sigaction.c (SET_SA_RESTORER): Clear sa_restorer for vDSO case. * sysdeps/unix/sysv/linux/i386/tst-bz21269.c: New file.
This commit is contained in:
Adhemerval Zanella
parent
8d965cde7a
commit
68448be208
@ -1,3 +1,11 @@
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2018-03-03 Adhemerval Zanella <adhemerval.zanella@linaro.org>
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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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2018-03-03 Samuel Thibault <samuel.thibault@ens-lyon.org>
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* scripts/check-installed-headers.sh: Ignore Hurd and Mach headers.
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@ -3,6 +3,9 @@ default-abi := 32
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ifeq ($(subdir),misc)
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sysdep_routines += ioperm iopl vm86
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tests += tst-bz21269
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$(objpfx)tst-bz21269: $(shared-thread-library)
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endif
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ifeq ($(subdir),elf)
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@ -42,7 +42,6 @@ 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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/* 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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@ -65,6 +64,8 @@ __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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233
sysdeps/unix/sysv/linux/i386/tst-bz21269.c
Normal file
233
sysdeps/unix/sysv/linux/i386/tst-bz21269.c
Normal file
@ -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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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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<http://www.gnu.org/licenses/>. */
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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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- 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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#include <stdatomic.h>
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#include <asm/ldt.h>
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#include <linux/futex.h>
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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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#include <support/xunistd.h>
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#include <support/check.h>
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#include <support/xthread.h>
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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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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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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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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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static jmp_buf jmpbuf;
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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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/* 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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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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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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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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xset_thread_area (low_user_desc);
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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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/* 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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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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/* 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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/* 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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/* 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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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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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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pthread_t thread;
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unsigned short orig_ss;
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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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thread = xpthread_create (0, threadproc, 0);
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asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
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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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/* 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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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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xmodify_ldt (0x11, &desc, sizeof (desc));
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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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asm volatile ("mov %0, %%ss" : : "r" (0x7));
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/* Fire up thread modify_ldt call. */
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atomic_store (&ftx, 2);
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while (atomic_load (&ftx) != 0)
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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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atomic_store (&ftx, 100);
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futex ((int*) &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
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xpthread_join (thread);
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return 0;
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}
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#include <support/test-driver.c>
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