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Steven Rostedt (VMware) dc912c3035 x86/ftrace: Fix ebp in ftrace_regs_caller that screws up unwinder
Fengguang Wu's zero day bot triggered a stack unwinder dump. This can
be easily triggered when CONFIG_FRAME_POINTERS is enabled and -mfentry
is in use on x86_32.

 ># cd /sys/kernel/debug/tracing
 ># echo 'p:schedule schedule' > kprobe_events
 ># echo stacktrace > events/kprobes/schedule/trigger

This is because the code that implemented fentry in the ftrace_regs_caller
tried to use the least amount of #ifdefs, and modified ebp when
CC_USE_FENTRY was defined to point to the parent ip as it does when
CC_USE_FENTRY is not defined. But when CONFIG_FRAME_POINTERS is set, it
corrupts the ebp register for this frame while doing the tracing.

NOTE, it does not corrupt ebp in any other way. It is just a bad frame
pointer when calling into the tracing infrastructure. The original ebp is
restored before returning from the fentry call. But if a stack trace is
performed inside the tracing, the unwinder will notice the bad ebp.

Instead of toying with ebp with CC_USING_FENTRY, just slap the parent ip
into the second parameter (%edx), and have an #else that does it the
original way.

The unwinder will unfortunately miss the function being traced, as the
stack frame is not set up yet for it, as it is for x86_64. But fixing that
is a bit more complex and did not work before anyway.

This has been tested with and without FRAME_POINTERS being set while using
-mfentry, as well as using an older compiler that uses mcount.

Analyzed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Fixes: 644e0e8dc7 ("x86/ftrace: Add -mfentry support to x86_32 with DYNAMIC_FTRACE set")
Reported-by: kernel test robot <fengguang.wu@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lists.01.org/pipermail/lkp/2017-April/006165.html
Link: http://lkml.kernel.org/r/20170420172236.7af7f6e5@gandalf.local.home
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2017-04-21 09:48:16 +02:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-14 21:31:23 -07:00
arch x86/ftrace: Fix ebp in ftrace_regs_caller that screws up unwinder 2017-04-21 09:48:16 +02:00
block blk-mq-sched: don't run the queue async from blk_mq_try_issue_directly() 2017-03-14 11:51:59 -06:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
drivers SCSI fixes on 20170321 2017-03-21 13:10:17 -07:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs f2fs: combine nat_bits and free_nid_bitmap cache 2017-03-20 10:00:18 -04:00
include debug: Avoid setting BUGFLAG_WARNING twice 2017-04-14 10:20:13 +02:00
init Change get_random_{int,log} to use the CRNG used by /dev/urandom and 2017-03-11 09:08:47 -08:00
ipc Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
kernel Merge branch 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-18 08:33:44 -07:00
lib debug: Add _ONCE() logic to report_bug() 2017-03-30 09:37:20 +02:00
mm mm, swap: Remove WARN_ON_ONCE() in free_swap_slot() 2017-03-21 14:13:19 -07:00
net NFS client fixes for 4.11 2017-03-17 14:16:22 -07:00
samples Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-03-03 11:38:56 -08:00
scripts Merge branch 'akpm' (patches from Andrew) 2017-03-10 08:34:42 -08:00
security Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
sound scripts/spelling.txt: add "disble(d)" pattern and fix typo instances 2017-03-09 17:01:09 -08:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-17 13:59:52 -07:00
usr kbuild: initramfs cleanup, set target from Kconfig 2017-01-05 09:40:16 -08:00
virt KVM: arm/arm64: VGIC: Fix command handling while ITS being disabled 2017-03-07 15:44:08 +00:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap mailmap: add codeaurora.org names for nameless email commits 2017-01-10 18:31:55 -08:00
COPYING
CREDITS MAINTAINERS: Remove old e-mail address 2017-02-13 12:24:56 -05:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig
MAINTAINERS MAINTAINERS: usb251xb: remove reference inexistent file 2017-03-09 10:34:16 +01:00
Makefile Linux 4.11-rc3 2017-03-19 19:09:39 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.