linux-kernel - Re: [RFC 00/31] objtool, livepatch: Livepatch module generation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZtsJ9qIPcADVce2i@redhat.com>
Date: Fri, 6 Sep 2024 09:56:06 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, Miroslav Benes <mbenes@...e.cz>,
	Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Song Liu <song@...nel.org>
Subject: Re: [RFC 00/31] objtool, livepatch: Livepatch module generation

On Mon, Sep 02, 2024 at 08:59:43PM -0700, Josh Poimboeuf wrote:
> Hi,
> 
> Here's a new way to build livepatch modules called klp-build.
> 
> I started working on it when I realized that objtool already does 99% of
> the work needed for detecting function changes.
> 
> This is similar in concept to kpatch-build, but the implementation is
> much cleaner.
> 
> Personally I still have reservations about the "source-based" approach
> (klp-convert and friends), including the fragility and performance
> concerns of -flive-patching.  I would submit that klp-build might be
> considered the "official" way to make livepatch modules.
> 
> Please try it out and let me know what you think.  Based on v6.10.
> 
> Also avaiable at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git klp-build-rfc
> 
> [ ... snip ... ]

Hi Josh,

A few minor build complaints on my system:

  $ make tools/objtool/check.o
    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    INSTALL libsubcmd_headers
    CC      /home/jolawren/src/linux/tools/objtool/check.o
  check.c: In function ‘is_livepatch_module’:
  check.c:661:16: error: implicit declaration of function ‘memmem’; did you mean ‘memset’? [-Werror=implicit-function-declaration]
    661 |         return memmem(sec->data->d_buf, sec_size(sec), "livepatch=Y", 12);
        |                ^~~~~~
        |                memset
  In function ‘is_first_func_insn’,
      inlined from ‘add_jump_destinations’ at check.c:1640:7,
      inlined from ‘decode_sections’ at check.c:2461:2:
  check.c:1498:17: error: ‘dest_insn’ may be used uninitialized [-Werror=maybe-uninitialized]
   1498 |         if (insn->offset == func->offset)
        |             ~~~~^~~~~~~~
  check.c: In function ‘decode_sections’:
  check.c:1522:37: note: ‘dest_insn’ was declared here
   1522 |                 struct instruction *dest_insn;
        |                                     ^~~~~~~~~
  cc1: all warnings being treated as errors
  make[4]: *** [/home/jolawren/src/linux/tools/build/Makefile.build:106: /home/jolawren/src/linux/tools/objtool/check.o] Error 1
  make[3]: *** [Makefile:78: /home/jolawren/src/linux/tools/objtool/objtool-in.o] Error 2
  make[2]: *** [Makefile:72: objtool] Error 2
  make[1]: *** [/home/jolawren/src/linux/Makefile:1378: tools/objtool] Error 2
  make: *** [Makefile:240: __sub-make] Error 2


  $ make tools/objtool/klp-diff.o
    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    INSTALL libsubcmd_headers
    CC      /home/jolawren/src/linux/tools/objtool/check.o
  check.c: In function ‘is_livepatch_module’:
  check.c:661:16: error: implicit declaration of function ‘memmem’; did you mean ‘memset’? [-Werror=implicit-function-declaration]
    661 |         return memmem(sec->data->d_buf, sec_size(sec), "livepatch=Y", 12);
        |                ^~~~~~
        |                memset
  In function ‘is_first_func_insn’,
      inlined from ‘add_jump_destinations’ at check.c:1640:7,
      inlined from ‘decode_sections’ at check.c:2461:2:
  check.c:1498:17: error: ‘dest_insn’ may be used uninitialized [-Werror=maybe-uninitialized]
   1498 |         if (insn->offset == func->offset)
        |             ~~~~^~~~~~~~
  check.c: In function ‘decode_sections’:
  check.c:1522:37: note: ‘dest_insn’ was declared here
   1522 |                 struct instruction *dest_insn;
        |                                     ^~~~~~~~~
  cc1: all warnings being treated as errors
  make[4]: *** [/home/jolawren/src/linux/tools/build/Makefile.build:106: /home/jolawren/src/linux/tools/objtool/check.o] Error 1
  make[3]: *** [Makefile:78: /home/jolawren/src/linux/tools/objtool/objtool-in.o] Error 2
  make[2]: *** [Makefile:72: objtool] Error 2
  make[1]: *** [/home/jolawren/src/linux/Makefile:1378: tools/objtool] Error 2
  make: *** [Makefile:240: __sub-make] Error 2


In the case of klp-diff.c, adding #include <string.h> will provide the
memmem prototype.  For both files, I needed to #define _GNU_SOURCE for
that prototype though.

For the other complaint, I just set struct instruction *dest_insn = NULL
at the top of the for loop, but perhaps the code could be refactored to
clarify the situation to the compiler if you prefer not to do that.

More info:

  $ gcc --version
  gcc (GCC) 12.3.1 20230508 (Red Hat 12.3.1-1)

  And kernel .config is attached.

--
Joe

View attachment ".config" of type "text/plain" (241855 bytes)