Commit Graph

18 Commits

Author SHA1 Message Date
Josh Poimboeuf 9eb719855f objtool: Fix cross-build
Stephen Rothwell reported this cross-compilation build failure:

| In file included from orc_dump.c:19:0:
| orc.h:21:10: fatal error: asm/orc_types.h: No such file or directory
| ...

Caused by:

  6a77cff819 ("objtool: Move synced files to their original relative locations")

Use the proper arch header files location, not the host-arch location.

Bisected-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux-Next Mailing List <linux-next@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171108030152.bd76eahiwjwjt3kp@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-11-08 10:06:08 +01:00
Josh Poimboeuf 3bd51c5a37 objtool: Move kernel headers/code sync check to a script
Replace the nasty diff checks in the objtool Makefile with a clean bash
script, and make the warnings more specific.

Heavily inspired by tools/perf/check-headers.sh.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ab015f15ccd8c0c6008493c3c6ee3d495eaf2927.1509974346.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-11-07 10:48:34 +01:00
Josh Poimboeuf 6a77cff819 objtool: Move synced files to their original relative locations
This will enable more straightforward comparisons, and it also makes the
files 100% identical.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/407b2aaa317741f48fcf821592c0e96ab3be1890.1509974346.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-11-07 10:48:23 +01:00
Greg Kroah-Hartman b24413180f License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-02 11:10:55 +01:00
Josh Poimboeuf 21ec3bf6ae objtool: Disable GCC '-Wpacked' warnings
Objtool is failing to build with GCC 4.4.7 due to the following
warnings:

  cc1: warnings being treated as errors
  In file included from orc.h:21,
                   from orc_gen.c:21:
  orc_types.h:86: error: packed attribute is unnecessary for ‘sp_offset’
  orc_types.h:87: error: packed attribute is unnecessary for ‘bp_offset’
  orc_types.h:88: error: packed attribute is unnecessary for ‘sp_reg’

I suspect those warnings are a GCC bug.  But -Wpacked isn't very useful
anyway, so just disable it.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 627fce1480 ("objtool: Add ORC unwind table generation")
Link: http://lkml.kernel.org/r/76d85d7b5a87566465095c500bce222ff5d7b146.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-07-28 08:33:32 +02:00
Josh Poimboeuf 39358a033b objtool, x86: Add facility for asm code to provide unwind hints
Some asm (and inline asm) code does special things to the stack which
objtool can't understand.  (Nor can GCC or GNU assembler, for that
matter.)  In such cases we need a facility for the code to provide
annotations, so the unwinder can unwind through it.

This provides such a facility, in the form of unwind hints.  They're
similar to the GNU assembler .cfi* directives, but they give more
information, and are needed in far fewer places, because objtool can
fill in the blanks by following branches and adjusting the stack pointer
for pushes and pops.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/0f5f3c9104fca559ff4088bece1d14ae3bca52d5.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-07-18 10:57:44 +02:00
Josh Poimboeuf baa41469a7 objtool: Implement stack validation 2.0
This is a major rewrite of objtool.  Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-30 10:19:19 +02:00
Uwe Kleine-König e19b7cee02 make use of make variable CURDIR instead of calling pwd
make already provides the current working directory in a variable, so make
use of it instead of forking a shell. Also replace usage of PWD by
CURDIR. PWD is provided by most shells, but not all, so this makes the
build system more robust.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Michal Marek <mmarek@suse.com>
2016-12-11 12:12:56 +01:00
Josh Poimboeuf 2af04ea545 objtool: Un-capitalize "Warning" for out-of-sync instruction decoder
Change "Warning" to "warning" to make it look more like a GCC warning.
Hopefully that will be enough to help the 0-day bot or other automated
tools catch this warning earlier before it ends up in Linus's tree.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b1669f391a5db91040427fd9f8e1e79db18f9709.1469751119.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-07-29 16:57:16 +02:00
Josh Poimboeuf 60cbdf5d05 tools build: Fix objtool build with ARCH=x86_64
The objtool build fails in a cross-compiled environment on a non-x86
host with "ARCH=x86_64":

  tools/objtool/objtool-in.o: In function `decode_instructions':
  tools/objtool/builtin-check.c:276: undefined reference to `arch_decode_instruction'

We could override the ARCH environment variable and change it back to
x86, similar to what the objtool Makefile was doing before; but it's
tricky to override environment variables consistently.

Instead, take a similar approach used by the Linux top-level Makefile
and introduce a SRCARCH Makefile variable which evaluates to "x86" when
ARCH is either "x86_64" or "x86".

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160722191920.ej62fnspnqurbaa7@treble
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-07-22 16:37:44 -03:00
Arnaldo Carvalho de Melo 0cf6eb603b objtool: Always use host headers
From a conversation with Josh:

From http://lkml.kernel.org/r/20160722034118.guckaniobf3f7czc@treble :

It needs to be compiled with the host (powerpc) compiler, but then it
needs to disassemble target (x86) files.

 ----

So use HOSTARCH instead of ARCH.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20160722034118.guckaniobf3f7czc@treble
Link: http://lkml.kernel.org/n/tip-le1m1yzxnfpt3msbblu40nm8@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-07-22 16:28:46 -03:00
Arnaldo Carvalho de Melo 630e7a2904 objtool: Use tools/scripts/Makefile.arch to get ARCH and HOSTARCH
objtool's Makefile was setting up ARCH but fixing up just the x86_64 ->
x86, using Makefile.arch will do the necessary fixups for all arches.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-hbq0bbh03u2b722vozcyql31@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-07-22 16:28:25 -03:00
Arnaldo Carvalho de Melo 4a0982f941 objtool: Add -I$(srctree)/tools/arch/$(ARCH)/include/uapi
So that it can find asm/bitsperlong.h to get the __BITS_PER_LONG
definition.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-pr3pvskh65pey4po7t122z4j@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-07-15 17:29:20 -03:00
Arnaldo Carvalho de Melo 1a4bf28573 objtool: Avoid checking code drift on busybox's diff
That doesn't have -I to match lines.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-1zqv1h6okt70e2huokkdtf1u@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-07-13 23:08:54 -03:00
Jan Beulich 2e51f26245 objtool: Allow building with older libelf
The switch to elf_getshdr{num,strndx} post-dates the oldest tool chain
the kernel is supposed to be able to build with, so try to cope with
such an environment.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: <stable@vger.kernel.org> # for v4.6
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/732dae6872b7ff187d94f22bb699a12849d3fe04.1463430618.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-05-17 10:42:46 +02:00
Josh Poimboeuf d435fb5ef7 objtool: Compile with debugging symbols
Compile objtool with debugging symbols ('-g') to help tools like perf
and gdb understand what it's doing.  Combined with '-O2', it's not
always helpful, but it's better than nothing.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/c295e9ee9ed360dc8b2e1d180c859f11cfc151ef.1457502970.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-03-09 10:48:08 +01:00
Josh Poimboeuf c1d45c3abd objtool: Support CROSS_COMPILE
When building with CONFIG_STACK_VALIDATION on a ppc64le host with an x86
cross-compiler, Stephen Rothwell saw the following objtool build errors:

    DESCEND  objtool
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/builtin-check.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/special.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/elf.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/objtool.o
    MKDIR    /home/sfr/next/x86_64_allmodconfig/tools/objtool/arch/x86/insn/
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/libstring.o
  elf.c:22:23: fatal error: sys/types.h: No such file or directory
  compilation terminated.
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/exec-cmd.o
    CC       /home/sfr/next/x86_64_allmodconfig/tools/objtool/help.o
  builtin-check.c:28:20: fatal error: string.h: No such file or directory
  compilation terminated.
  objtool.c:28:19: fatal error: stdio.h: No such file or directory
  compilation terminated.

It fails to build because it tries to compile objtool with the
cross-compiler instead of the host compiler.

Ensure that it always uses the host compiler by ignoring CROSS_COMPILE.

In order to do that properly, the libsubcmd.a library needs to be built
in tools/objtool/ rather than tools/lib/subcmd/.  The latter directory
contains the cross-compiled version which is needed for perf and
possibly other tools.

Note that cross-compiling for x86 on a _big_ endian system would result
in a bunch of false positive objtool warnings during the kernel build
because it isn't endian-aware.  But that's generally a rare edge case
and there haven't been any reports of anybody needing that.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/55b63eefc347f1bb28573f972d8d1adbf1f1c31d.1456962210.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-03-03 16:13:00 +01:00
Josh Poimboeuf 442f04c34a objtool: Add tool to perform compile-time stack metadata validation
This adds a host tool named objtool which has a "check" subcommand which
analyzes .o files to ensure the validity of stack metadata.  It enforces
a set of rules on asm code and C inline assembly code so that stack
traces can be reliable.

For each function, it recursively follows all possible code paths and
validates the correct frame pointer state at each instruction.

It also follows code paths involving kernel special sections, like
.altinstructions, __jump_table, and __ex_table, which can add
alternative execution paths to a given instruction (or set of
instructions).  Similarly, it knows how to follow switch statements, for
which gcc sometimes uses jump tables.

Here are some of the benefits of validating stack metadata:

a) More reliable stack traces for frame pointer enabled kernels

   Frame pointers are used for debugging purposes.  They allow runtime
   code and debug tools to be able to walk the stack to determine the
   chain of function call sites that led to the currently executing
   code.

   For some architectures, frame pointers are enabled by
   CONFIG_FRAME_POINTER.  For some other architectures they may be
   required by the ABI (sometimes referred to as "backchain pointers").

   For C code, gcc automatically generates instructions for setting up
   frame pointers when the -fno-omit-frame-pointer option is used.

   But for asm code, the frame setup instructions have to be written by
   hand, which most people don't do.  So the end result is that
   CONFIG_FRAME_POINTER is honored for C code but not for most asm code.

   For stack traces based on frame pointers to be reliable, all
   functions which call other functions must first create a stack frame
   and update the frame pointer.  If a first function doesn't properly
   create a stack frame before calling a second function, the *caller*
   of the first function will be skipped on the stack trace.

   For example, consider the following example backtrace with frame
   pointers enabled:

     [<ffffffff81812584>] dump_stack+0x4b/0x63
     [<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
     [<ffffffff8127f568>] seq_read+0x108/0x3e0
     [<ffffffff812cce62>] proc_reg_read+0x42/0x70
     [<ffffffff81256197>] __vfs_read+0x37/0x100
     [<ffffffff81256b16>] vfs_read+0x86/0x130
     [<ffffffff81257898>] SyS_read+0x58/0xd0
     [<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

   It correctly shows that the caller of cmdline_proc_show() is
   seq_read().

   If we remove the frame pointer logic from cmdline_proc_show() by
   replacing the frame pointer related instructions with nops, here's
   what it looks like instead:

     [<ffffffff81812584>] dump_stack+0x4b/0x63
     [<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
     [<ffffffff812cce62>] proc_reg_read+0x42/0x70
     [<ffffffff81256197>] __vfs_read+0x37/0x100
     [<ffffffff81256b16>] vfs_read+0x86/0x130
     [<ffffffff81257898>] SyS_read+0x58/0xd0
     [<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

   Notice that cmdline_proc_show()'s caller, seq_read(), has been
   skipped.  Instead the stack trace seems to show that
   cmdline_proc_show() was called by proc_reg_read().

   The benefit of "objtool check" here is that because it ensures that
   *all* functions honor CONFIG_FRAME_POINTER, no functions will ever[*]
   be skipped on a stack trace.

   [*] unless an interrupt or exception has occurred at the very
       beginning of a function before the stack frame has been created,
       or at the very end of the function after the stack frame has been
       destroyed.  This is an inherent limitation of frame pointers.

b) 100% reliable stack traces for DWARF enabled kernels

   This is not yet implemented.  For more details about what is planned,
   see tools/objtool/Documentation/stack-validation.txt.

c) Higher live patching compatibility rate

   This is not yet implemented.  For more details about what is planned,
   see tools/objtool/Documentation/stack-validation.txt.

To achieve the validation, "objtool check" enforces the following rules:

1. Each callable function must be annotated as such with the ELF
   function type.  In asm code, this is typically done using the
   ENTRY/ENDPROC macros.  If objtool finds a return instruction
   outside of a function, it flags an error since that usually indicates
   callable code which should be annotated accordingly.

   This rule is needed so that objtool can properly identify each
   callable function in order to analyze its stack metadata.

2. Conversely, each section of code which is *not* callable should *not*
   be annotated as an ELF function.  The ENDPROC macro shouldn't be used
   in this case.

   This rule is needed so that objtool can ignore non-callable code.
   Such code doesn't have to follow any of the other rules.

3. Each callable function which calls another function must have the
   correct frame pointer logic, if required by CONFIG_FRAME_POINTER or
   the architecture's back chain rules.  This can by done in asm code
   with the FRAME_BEGIN/FRAME_END macros.

   This rule ensures that frame pointer based stack traces will work as
   designed.  If function A doesn't create a stack frame before calling
   function B, the _caller_ of function A will be skipped on the stack
   trace.

4. Dynamic jumps and jumps to undefined symbols are only allowed if:

   a) the jump is part of a switch statement; or

   b) the jump matches sibling call semantics and the frame pointer has
      the same value it had on function entry.

   This rule is needed so that objtool can reliably analyze all of a
   function's code paths.  If a function jumps to code in another file,
   and it's not a sibling call, objtool has no way to follow the jump
   because it only analyzes a single file at a time.

5. A callable function may not execute kernel entry/exit instructions.
   The only code which needs such instructions is kernel entry code,
   which shouldn't be be in callable functions anyway.

   This rule is just a sanity check to ensure that callable functions
   return normally.

It currently only supports x86_64.  I tried to make the code generic so
that support for other architectures can hopefully be plugged in
relatively easily.

On my Lenovo laptop with a i7-4810MQ 4-core/8-thread CPU, building the
kernel with objtool checking every .o file adds about three seconds of
total build time.  It hasn't been optimized for performance yet, so
there are probably some opportunities for better build performance.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/f3efb173de43bd067b060de73f856567c0fa1174.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-29 08:35:12 +01:00