72 lines
2.7 KiB
Diff
72 lines
2.7 KiB
Diff
From df29db0bec24211cfc917db52024bf8deecac2c9 Mon Sep 17 00:00:00 2001
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From: Mike Frysinger <vapier@gentoo.org>
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Date: Wed, 15 Mar 2017 23:59:31 -0700
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Subject: [PATCH 10] posix_spawn: use a larger min stack for -fstack-check
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[BZ #21253]
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When glibc is built with -fstack-check, trying to use posix_spawn can
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lead to segfaults due to gcc internally probing stack memory too far.
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The new spawn API will allocate a minimum of 1 page, but the stack
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checking logic might probe a couple of pages. When it tries to walk
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them, everything falls apart.
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The gcc internal docs [1] state the default interval checking is one
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page. Which means we need two pages (the current one, and the next
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probed). No target currently defines it larger.
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Further, it mentions that the default minimum stack size needed to
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recover from an overflow is 4/8KiB for sjlj or 8/12KiB for others.
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But some Linux targets (like mips and ppc) go up to 16KiB (and some
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non-Linux targets go up to 24KiB).
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Let's create each child with a minimum of 32KiB slack space to support
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them all, and give us future breathing room.
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No test is added as existing ones crash. Even a simple call is
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enough to trigger the problem:
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char *argv[] = { "/bin/ls", NULL };
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posix_spawn(NULL, "/bin/ls", NULL, NULL, argv, NULL);
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[1] https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gccint/Stack-Checking.html
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(cherry picked from commit 21f042c804835d1f7a4a8e06f2c93ca35a182042)
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---
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ChangeLog | 6 ++++++
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sysdeps/unix/sysv/linux/spawni.c | 5 +++++
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2 files changed, 11 insertions(+)
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diff --git a/ChangeLog b/ChangeLog
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index 321bf53..b37a054 100644
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--- a/ChangeLog
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+++ b/ChangeLog
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@@ -1,3 +1,9 @@
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+2017-04-03 Mike Frysinger <vapier@gentoo.org>
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+
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+ [BZ #21253]
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+ * sysdeps/unix/sysv/linux/spawni.c (__spawnix): Increase argv_size
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+ slack space by 32KiB.
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+
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2017-04-03 Wladimir van der Laan <laanwj@gmail.com>
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[BZ# 21338]
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diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c
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index c96aac8..29d8f25 100644
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--- a/sysdeps/unix/sysv/linux/spawni.c
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+++ b/sysdeps/unix/sysv/linux/spawni.c
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@@ -319,6 +319,11 @@ __spawnix (pid_t * pid, const char *file,
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/* Add a slack area for child's stack. */
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size_t argv_size = (argc * sizeof (void *)) + 512;
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+ /* We need at least a few pages in case the compiler's stack checking is
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+ enabled. In some configs, it is known to use at least 24KiB. We use
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+ 32KiB to be "safe" from anything the compiler might do. Besides, the
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+ extra pages won't actually be allocated unless they get used. */
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+ argv_size += (32 * 1024);
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size_t stack_size = ALIGN_UP (argv_size, GLRO(dl_pagesize));
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void *stack = __mmap (NULL, stack_size, prot,
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MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
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--
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2.7.4.GIT
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