Commit Graph

23 Commits

Author SHA1 Message Date
Aaron Plattner
e959c279d3 objtool: Propagate early errors
If objtool runs into a problem that causes it to exit early, the overall
tool still returns a status code of 0, which causes the build to
continue as if nothing went wrong.

Note this only affects early errors, as later errors are still ignored
by check().

Fixes: b51277eb97 ("objtool: Ditch subcommands")
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Link: https://lore.kernel.org/r/cb6a28832d24b2ebfafd26da9abb95f874c83045.1696355111.git.aplattner@nvidia.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2023-10-05 17:01:11 -07:00
Peter Zijlstra
1c34496e58 objtool: Remove instruction::list
Replace the instruction::list by allocating instructions in arrays of
256 entries and stringing them together by (amortized) find_insn().
This shrinks instruction by 16 bytes and brings it down to 128.

 struct instruction {
-	struct list_head           list;                 /*     0    16 */
-	struct hlist_node          hash;                 /*    16    16 */
-	struct list_head           call_node;            /*    32    16 */
-	struct section *           sec;                  /*    48     8 */
-	long unsigned int          offset;               /*    56     8 */
-	/* --- cacheline 1 boundary (64 bytes) --- */
-	long unsigned int          immediate;            /*    64     8 */
-	unsigned int               len;                  /*    72     4 */
-	u8                         type;                 /*    76     1 */
-
-	/* Bitfield combined with previous fields */
+	struct hlist_node          hash;                 /*     0    16 */
+	struct list_head           call_node;            /*    16    16 */
+	struct section *           sec;                  /*    32     8 */
+	long unsigned int          offset;               /*    40     8 */
+	long unsigned int          immediate;            /*    48     8 */
+	u8                         len;                  /*    56     1 */
+	u8                         prev_len;             /*    57     1 */
+	u8                         type;                 /*    58     1 */
+	s8                         instr;                /*    59     1 */
+	u32                        idx:8;                /*    60: 0  4 */
+	u32                        dead_end:1;           /*    60: 8  4 */
+	u32                        ignore:1;             /*    60: 9  4 */
+	u32                        ignore_alts:1;        /*    60:10  4 */
+	u32                        hint:1;               /*    60:11  4 */
+	u32                        save:1;               /*    60:12  4 */
+	u32                        restore:1;            /*    60:13  4 */
+	u32                        retpoline_safe:1;     /*    60:14  4 */
+	u32                        noendbr:1;            /*    60:15  4 */
+	u32                        entry:1;              /*    60:16  4 */
+	u32                        visited:4;            /*    60:17  4 */
+	u32                        no_reloc:1;           /*    60:21  4 */

-	u16                        dead_end:1;           /*    76: 8  2 */
-	u16                        ignore:1;             /*    76: 9  2 */
-	u16                        ignore_alts:1;        /*    76:10  2 */
-	u16                        hint:1;               /*    76:11  2 */
-	u16                        save:1;               /*    76:12  2 */
-	u16                        restore:1;            /*    76:13  2 */
-	u16                        retpoline_safe:1;     /*    76:14  2 */
-	u16                        noendbr:1;            /*    76:15  2 */
-	u16                        entry:1;              /*    78: 0  2 */
-	u16                        visited:4;            /*    78: 1  2 */
-	u16                        no_reloc:1;           /*    78: 5  2 */
+	/* XXX 10 bits hole, try to pack */

-	/* XXX 2 bits hole, try to pack */
-	/* Bitfield combined with next fields */
-
-	s8                         instr;                /*    79     1 */
-	struct alt_group *         alt_group;            /*    80     8 */
-	struct instruction *       jump_dest;            /*    88     8 */
-	struct instruction *       first_jump_src;       /*    96     8 */
+	/* --- cacheline 1 boundary (64 bytes) --- */
+	struct alt_group *         alt_group;            /*    64     8 */
+	struct instruction *       jump_dest;            /*    72     8 */
+	struct instruction *       first_jump_src;       /*    80     8 */
 	union {
-		struct symbol *    _call_dest;           /*   104     8 */
-		struct reloc *     _jump_table;          /*   104     8 */
-	};                                               /*   104     8 */
-	struct alternative *       alts;                 /*   112     8 */
-	struct symbol *            sym;                  /*   120     8 */
-	/* --- cacheline 2 boundary (128 bytes) --- */
-	struct stack_op *          stack_ops;            /*   128     8 */
-	struct cfi_state *         cfi;                  /*   136     8 */
+		struct symbol *    _call_dest;           /*    88     8 */
+		struct reloc *     _jump_table;          /*    88     8 */
+	};                                               /*    88     8 */
+	struct alternative *       alts;                 /*    96     8 */
+	struct symbol *            sym;                  /*   104     8 */
+	struct stack_op *          stack_ops;            /*   112     8 */
+	struct cfi_state *         cfi;                  /*   120     8 */

-	/* size: 144, cachelines: 3, members: 28 */
-	/* sum members: 142 */
-	/* sum bitfield members: 14 bits, bit holes: 1, sum bit holes: 2 bits */
-	/* last cacheline: 16 bytes */
+	/* size: 128, cachelines: 2, members: 29 */
+	/* sum members: 124 */
+	/* sum bitfield members: 22 bits, bit holes: 1, sum bit holes: 10 bits */
 };

pre:	5:38.18 real,   213.25 user,    124.90 sys,     23449040 mem
post:	5:03.34 real,   210.75 user,    88.80 sys,      20241232 mem

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build only
Tested-by: Thomas Weißschuh <linux@weissschuh.net> # compile and run
Link: https://lore.kernel.org/r/20230208172245.851307606@infradead.org
2023-02-23 09:21:44 +01:00
Peter Zijlstra
00abd38408 objtool: Add .call_sites section
In preparation for call depth tracking provide a section which collects all
direct calls.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111146.016511961@infradead.org
2022-10-17 16:41:07 +02:00
Peter Zijlstra
d9e9d23006 x86,objtool: Create .return_sites
Find all the return-thunk sites and record them in a .return_sites
section such that the kernel can undo this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
2022-06-27 10:33:58 +02:00
Josh Poimboeuf
b51277eb97 objtool: Ditch subcommands
Objtool has a fairly singular focus.  It runs on object files and does
validations and transformations which can be combined in various ways.
The subcommand model has never been a good fit, making it awkward to
combine and remove options.

Remove the "check" and "orc" subcommands in favor of a more traditional
cmdline option model.  This makes it much more flexible to use, and
easier to port individual features to other arches.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/5c61ebf805e90aefc5fa62bc63468ffae53b9df6.1650300597.git.jpoimboe@redhat.com
2022-04-22 12:32:01 +02:00
Josh Poimboeuf
2daf7faba7 objtool: Reorganize cmdline options
Split the existing options into two groups: actions, which actually do
something; and options, which modify the actions in some way.

Also there's no need to have short flags for all the non-action options.
Reserve short flags for the more important actions.

While at it:

- change a few of the short flags to be more intuitive

- make option descriptions more consistently descriptive

- sort options in the source like they are when printed

- move options to a global struct

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/9dcaa752f83aca24b1b21f0b0eeb28a0c181c0b0.1650300597.git.jpoimboe@redhat.com
2022-04-22 12:32:01 +02:00
Josh Poimboeuf
08feafe8d1 objtool: Fix function fallthrough detection for vmlinux
Objtool's function fallthrough detection only works on C objects.
The distinction between C and assembly objects no longer makes sense
with objtool running on vmlinux.o.

Now that copy_user_64.S has been fixed up, and an objtool sibling call
detection bug has been fixed, the asm code is in "compliance" and this
hack is no longer needed.  Remove it.

Fixes: ed53a0d971 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/b434cff98eca3a60dcc64c620d7d5d405a0f441c.1649718562.git.jpoimboe@redhat.com
2022-04-19 21:58:53 +02:00
Peter Zijlstra
89bc853eae objtool: Find unused ENDBR instructions
Find all ENDBR instructions which are never referenced and stick them
in a section such that the kernel can poison them, sealing the
functions from ever being an indirect call target.

This removes about 1-in-4 ENDBR instructions.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.763643193@infradead.org
2022-03-15 10:32:47 +01:00
Peter Zijlstra
988f01683c objtool: Fix pv_ops noinstr validation
Boris reported that in one of his randconfig builds, objtool got
infinitely stuck. Turns out there's trivial list corruption in the
pv_ops tracking when a function is both in a static table and in a code
assignment.

Avoid re-adding function to the pv_ops[] lists when they're already on
it.

Fixes: db2b0c5d7b ("objtool: Support pv_opsindirect calls for noinstr")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/20211202204534.GA16608@worktop.programming.kicks-ass.net
2021-12-03 09:11:42 +01:00
Peter Zijlstra
db2b0c5d7b objtool: Support pv_opsindirect calls for noinstr
Normally objtool will now follow indirect calls; there is no need.

However, this becomes a problem with noinstr validation; if there's an
indirect call from noinstr code, we very much need to know it is to
another noinstr function. Luckily there aren't many indirect calls in
entry code with the obvious exception of paravirt. As such, noinstr
validation didn't work with paravirt kernels.

In order to track pv_ops[] call targets, objtool reads the static
pv_ops[] tables as well as direct assignments to the pv_ops[] array,
provided the compiler makes them a single instruction like:

  bf87:       48 c7 05 00 00 00 00 00 00 00 00        movq   $0x0,0x0(%rip)
    bf92 <xen_init_spinlocks+0x5f>
    bf8a: R_X86_64_PC32     pv_ops+0x268

There are, as of yet, no warnings for when this goes wrong :/

Using the functions found with the above means, all pv_ops[] calls are
now subject to noinstr validation.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210624095149.118815755@infradead.org
2021-09-17 13:20:26 +02:00
Linus Torvalds
03b2cd72aa Objtool updates in this cycle were:
- Standardize the crypto asm code so that it looks like compiler-generated
    code to objtool - so that it can understand it. This enables unwinding
    from crypto asm code - and also fixes the last known remaining objtool
    warnings for LTO and more.
 
  - x86 decoder fixes: clean up and fix the decoder, and also extend it a bit
 
  - Misc fixes and cleanups
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'objtool-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool updates from Ingo Molnar:

 - Standardize the crypto asm code so that it looks like compiler-
   generated code to objtool - so that it can understand it. This
   enables unwinding from crypto asm code - and also fixes the last
   known remaining objtool warnings for LTO and more.

 - x86 decoder fixes: clean up and fix the decoder, and also extend it a
   bit

 - Misc fixes and cleanups

* tag 'objtool-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
  x86/crypto: Enable objtool in crypto code
  x86/crypto/sha512-ssse3: Standardize stack alignment prologue
  x86/crypto/sha512-avx2: Standardize stack alignment prologue
  x86/crypto/sha512-avx: Standardize stack alignment prologue
  x86/crypto/sha256-avx2: Standardize stack alignment prologue
  x86/crypto/sha1_avx2: Standardize stack alignment prologue
  x86/crypto/sha_ni: Standardize stack alignment prologue
  x86/crypto/crc32c-pcl-intel: Standardize jump table
  x86/crypto/camellia-aesni-avx2: Unconditionally allocate stack buffer
  x86/crypto/aesni-intel_avx: Standardize stack alignment prologue
  x86/crypto/aesni-intel_avx: Fix register usage comments
  x86/crypto/aesni-intel_avx: Remove unused macros
  objtool: Support asm jump tables
  objtool: Parse options from OBJTOOL_ARGS
  objtool: Collate parse_options() users
  objtool: Add --backup
  objtool,x86: More ModRM sugar
  objtool,x86: Rewrite ADD/SUB/AND
  objtool,x86: Support %riz encodings
  objtool,x86: Simplify register decode
  ...
2021-04-28 12:53:24 -07:00
Peter Zijlstra
43d5430ad7 objtool: Keep track of retpoline call sites
Provide infrastructure for architectures to rewrite/augment compiler
generated retpoline calls. Similar to what we do for static_call()s,
keep track of the instructions that are retpoline calls.

Use the same list_head, since a retpoline call cannot also be a
static_call.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.130805730@infradead.org
2021-04-02 12:45:27 +02:00
Peter Zijlstra
8ad15c6900 objtool: Add --backup
Teach objtool to write backups files, such that it becomes easier to
see what objtool did to the object file.

Backup files will be ${name}.orig.

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/YD4obT3aoXPWl7Ax@hirez.programming.kicks-ass.net
2021-03-06 12:44:23 +01:00
Linus Torvalds
414eece95b clang-lto for v5.12-rc1 (part2)
- Generate __mcount_loc in objtool (Peter Zijlstra)
 - Support running objtool against vmlinux.o (Sami Tolvanen)
 - Clang LTO enablement for x86 (Sami Tolvanen)
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Merge tag 'clang-lto-v5.12-rc1-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull more clang LTO updates from Kees Cook:
 "Clang LTO x86 enablement.

  Full disclosure: while this has _not_ been in linux-next (since it
  initially looked like the objtool dependencies weren't going to make
  v5.12), it has been under daily build and runtime testing by Sami for
  quite some time. These x86 portions have been discussed on lkml, with
  Peter, Josh, and others helping nail things down.

  The bulk of the changes are to get objtool working happily. The rest
  of the x86 enablement is very small.

  Summary:

   - Generate __mcount_loc in objtool (Peter Zijlstra)

   - Support running objtool against vmlinux.o (Sami Tolvanen)

   - Clang LTO enablement for x86 (Sami Tolvanen)"

Link: https://lore.kernel.org/lkml/20201013003203.4168817-26-samitolvanen@google.com/
Link: https://lore.kernel.org/lkml/cover.1611263461.git.jpoimboe@redhat.com/

* tag 'clang-lto-v5.12-rc1-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  kbuild: lto: force rebuilds when switching CONFIG_LTO
  x86, build: allow LTO to be selected
  x86, cpu: disable LTO for cpu.c
  x86, vdso: disable LTO only for vDSO
  kbuild: lto: postpone objtool
  objtool: Split noinstr validation from --vmlinux
  x86, build: use objtool mcount
  tracing: add support for objtool mcount
  objtool: Don't autodetect vmlinux.o
  objtool: Fix __mcount_loc generation with Clang's assembler
  objtool: Add a pass for generating __mcount_loc
2021-02-23 15:13:45 -08:00
Peter Zijlstra
99d0021569 objtool: Add a pass for generating __mcount_loc
Add the --mcount option for generating __mcount_loc sections
needed for dynamic ftrace. Using this pass requires the kernel to
be compiled with -mfentry and CC_USING_NOP_MCOUNT to be defined
in Makefile.

Link: https://lore.kernel.org/lkml/20200625200235.GQ4781@hirez.programming.kicks-ass.net/
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
[Sami: rebased, dropped config changes, fixed to actually use --mcount,
       and wrote a commit message.]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
2021-02-23 12:46:56 -08:00
Vasily Gorbik
7786032e52 objtool: Rework header include paths
Currently objtool headers are being included either by their base name
or included via ../ from a parent directory. In case of a base name usage:

 #include "warn.h"
 #include "arch_elf.h"

it does not make it apparent from which directory the file comes from.
To make it slightly better, and actually to avoid name clashes some arch
specific files have "arch_" suffix. And files from an arch folder have
to revert to including via ../ e.g:
 #include "../../elf.h"

With additional architectures support and the code base growth there is
a need for clearer headers naming scheme for multiple reasons:
1. to make it instantly obvious where these files come from (objtool
   itself / objtool arch|generic folders / some other external files),
2. to avoid name clashes of objtool arch specific headers, potential
   obtool arch generic headers and the system header files (there is
   /usr/include/elf.h already),
3. to avoid ../ includes and improve code readability.
4. to give a warm fuzzy feeling to developers who are mostly kernel
   developers and are accustomed to linux kernel headers arranging
   scheme.

Doesn't this make it instantly obvious where are these files come from?

 #include <objtool/warn.h>
 #include <arch/elf.h>

And doesn't it look nicer to avoid ugly ../ includes? Which also
guarantees this is elf.h from the objtool and not /usr/include/elf.h.

 #include <objtool/elf.h>

This patch defines and implements new objtool headers arranging
scheme. Which is:
- all generic headers go to include/objtool (similar to include/linux)
- all arch headers go to arch/$(SRCARCH)/include/arch (to get arch
  prefix). This is similar to linux arch specific "asm/*" headers but we
  are not abusing "asm" name and calling it what it is. This also helps
  to prevent name clashes (arch is not used in system headers or kernel
  exports).

To bring objtool to this state the following things are done:
1. current top level tools/objtool/ headers are moved into
   include/objtool/ subdirectory,
2. arch specific headers, currently only arch/x86/include/ are moved into
   arch/x86/include/arch/ and were stripped of "arch_" suffix,
3. new -I$(srctree)/tools/objtool/include include path to make
   includes like <objtool/warn.h> possible,
4. rewriting file includes,
5. make git not to ignore include/objtool/ subdirectory.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
2021-01-13 18:13:14 -06:00
Julien Thierry
6545eb030e objtool: Move object file loading out of check()
Structure objtool_file can be used by different subcommands. In fact
it already is, by check and orc.

Provide a function that allows to initialize objtool_file, that builtin
can call, without relying on check to do the correct setup for them and
explicitly hand the objtool_file to them.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
2020-09-01 17:19:07 -05:00
Matt Helsley
f15c648f20 objtool: Exit successfully when requesting help
When the user requests help it's not an error so do not exit with
a non-zero exit code. This is not especially useful for a user but
any script that might wish to check that objtool --help is at least
available can't rely on the exit code to crudely check that, for
example, building an objtool executable succeeds.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
2020-05-20 08:32:52 -05:00
Thomas Gleixner
1ccea77e2a treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13
Based on 2 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license as published by
  the free software foundation either version 2 of the license or at
  your option any later version this program is distributed in the
  hope that it will be useful but without any warranty without even
  the implied warranty of merchantability or fitness for a particular
  purpose see the gnu general public license for more details you
  should have received a copy of the gnu general public license along
  with this program if not see http www gnu org licenses

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license as published by
  the free software foundation either version 2 of the license or at
  your option any later version this program is distributed in the
  hope that it will be useful but without any warranty without even
  the implied warranty of merchantability or fitness for a particular
  purpose see the gnu general public license for more details [based]
  [from] [clk] [highbank] [c] you should have received a copy of the
  gnu general public license along with this program if not see http
  www gnu org licenses

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 355 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Jilayne Lovejoy <opensource@jilayne.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190519154041.837383322@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-21 11:28:45 +02:00
Kamalesh Babulal
6a93bb7e4a objtool: Print top level commands on incorrect usage
Print top-level objtool commands, along with the error on incorrect
command line usage. Objtool command line parser exit's with code 129,
for incorrect usage. Convert the cmd_usage() exit code also, to maintain
consistency across objtool.

After the patch:

  $ ./objtool -j

  Unknown option: -j

  usage: objtool COMMAND [ARGS]

  Commands:
     check   Perform stack metadata validation on an object file
     orc     Generate in-place ORC unwind tables for an object file

  $ echo $?
  129

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Acked-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/1507992474-16142-1-git-send-email-kamalesh@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-18 15:22:26 +02:00
Josh Poimboeuf
627fce1480 objtool: Add ORC unwind table generation
Now that objtool knows the states of all registers on the stack for each
instruction, it's straightforward to generate debuginfo for an unwinder
to use.

Instead of generating DWARF, generate a new format called ORC, which is
more suitable for an in-kernel unwinder.  See
Documentation/x86/orc-unwinder.txt for a more detailed description of
this new debuginfo format and why it's preferable to DWARF.

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/c9b9f01ba6c5ed2bdc9bb0957b78167fdbf9632e.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-07-18 10:57:43 +02:00
Arnaldo Carvalho de Melo
0061459744 objtool: Drop ARRAY_SIZE() definition, tools/include/linux/kernel.h has it now
And with the goodies present in the kernel.h counterpart, i.e. checking
that the parameter is an array at build time.

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-roiwxwgwgld4kygn65if60wa@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2017-04-19 13:01:44 -03:00
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