From: Marcos Paulo de Souza <mpdesouza@suse.de>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kbuild@vger.kernel.org,
Josh Poimboeuf <jpoimboe@kernel.org>,
Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
Marcos Paulo de Souza <mpdesouza@suse.com>
Subject: Re: [PATCH v7 00/10] livepatch: klp-convert tool
Date: Mon, 20 Mar 2023 17:15:41 -0300 [thread overview]
Message-ID: <20230320201541.2f6mchhogr3e4yrs@daedalus> (raw)
In-Reply-To: <ZBTNvEPrCcRj3F1C@redhat.com>
On Fri, Mar 17, 2023 at 04:29:48PM -0400, Joe Lawrence wrote:
> On Tue, Mar 14, 2023 at 05:23:56PM -0300, Marcos Paulo de Souza wrote:
> > On Mon, Mar 06, 2023 at 09:08:14AM -0500, Joe Lawrence wrote:
> > > Summary
> > > -------
> > >
> > > Livepatches may use symbols which are not contained in its own scope,
> > > and, because of that, may end up compiled with relocations that will
> > > only be resolved during module load. Yet, when the referenced symbols
> > > are not exported, solving this relocation requires information on the
> > > object that holds the symbol (either vmlinux or modules) and its
> > > position inside the object, as an object may contain multiple symbols
> > > with the same name. Providing such information must be done accordingly
> > > to what is specified in Documentation/livepatch/module-elf-format.txt.
> > >
> > > Currently, there is no trivial way to embed the required information as
> > > requested in the final livepatch elf object. klp-convert solves this
> > > problem in two different forms: (i) by relying on a symbol map, which is
> > > built during kernel compilation, to automatically infer the relocation
> > > targeted symbol, and, when such inference is not possible (ii) by using
> > > annotations in the elf object to convert the relocation accordingly to
> > > the specification, enabling it to be handled by the livepatch loader.
> > >
> > > Given the above, add support for symbol mapping in the form of a
> > > symbols.klp file; add klp-convert tool; integrate klp-convert tool into
> > > kbuild; make livepatch modules discernible during kernel compilation
> > > pipeline; add data-structure and macros to enable users to annotate
> > > livepatch source code; make modpost stage compatible with livepatches;
> > > update livepatch-sample and update documentation.
> > >
> > > The patch was tested under three use-cases:
> > >
> > > use-case 1: There is a relocation in the lp that can be automatically
> > > resolved by klp-convert. For example. see the saved_command_line
> > > variable in lib/livepatch/test_klp_convert2.c.
> > >
> > > use-case 2: There is a relocation in the lp that cannot be automatically
> > > resolved, as the name of the respective symbol appears in multiple
> > > objects. The livepatch contains an annotation to enable a correct
> > > relocation. See the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections
> > > in lib/livepatch/test_klp_convert{1,2}.c.
> > >
> > > use-case 3: There is a relocation in the lp that cannot be automatically
> > > resolved similarly as 2, but no annotation was provided in the
> > > livepatch, triggering an error during compilation. Reproducible by
> > > removing the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections in
> > > lib/livepatch/test_klp_convert{1,2}.c.
> > >
> > > Selftests have been added to exercise these klp-convert use-cases
> > > through several tests.
> > >
> > >
> > > Testing
> > > -------
> > >
> > > The patchset selftests build and execute on x86_64, s390x, and ppc64le
> > > for both default config (with added livepatch dependencies) and a larger
> > > RHEL-9-ish config.
> > >
> > > Using the Intel's Linux Kernel Performance tests's make.cross,
> > > klp-convert builds and processes livepatch .ko's for x86_64 ppc64le
> > > ppc32 s390 arm64 arches.
> > >
> > >
> > > Summary of changes in v7
> > > ------------------------
> > >
> > > - rebase for v6.2
> > > - combine ("livepatch: Add klp-convert tool") with ("livepatch: Add
> > > klp-convert annotation helpers")
> > > - combine ("kbuild: Support for symbols.klp creation") with ("modpost:
> > > Integrate klp-convert") to simplify Kbuild magic [Petr, Nicolas]
> > > - klp-convert: add safe_snprintf() (-Wsign-compare)
> > > - klp-convert: fix -Wsign-compare warnings
> > > - klp-convert: use calloc() where appropriate
> > > - klp-convert: copy ELF e_flags
> > > - selftests: fix various build warnings
> > > - klp-convert: WARN msg simplification, failed sanity checks, and sympos
> > > comment [Marcos]
> > > - klp-convert: fix elf_write_file() error paths [Petr]
> >
> > Thanks for the new version Joe. I've run the ksefltests on my x86 laptop, and it
> > succeed as expected, so
> >
> > Tested-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> >
>
> Thanks for the testing and reviews, Marcos.
>
> The selftests are the first level of testing... we should probably
> tackle a real or simulated CVE fix to see how well the tooling fits
> larger livepatches.
Our plan is to start testing new livepatches with klp-convert to ensure that it
works as expected, removing the need of kallsyms_lookup. Let's see how it goes
in the next few weeks.
>
> One complication that I can envision is symbol positioning. Currently,
> the klp-convert annotations are a direct mirror of the kernel's
> <obj,symbol,pos> tuple. It should be possible to make this a bit more
> user friendly for the livepatch developer if the annotations were
> <obj,file,symbol>, as derived from the vmlinux / module.tmp.ko symbol
> tables.
>
> For example, the following code:
>
> KLP_MODULE_RELOC(test_klp_convert_mod, test_klp_convert_mod_b.c) test_klp_convert_mod_relocs_b[] = {
> KLP_SYMPOS(homonym_string),
> KLP_SYMPOS(get_homonym_string),
> };
>
> could generate the following relocations:
>
> Relocation section '.rela.klp.module_relocs.test_klp_convert_mod.test_klp_convert_mod_b.c' at offset 0x1dc0 contains 2 entries:
> Offset Info Type Symbol's Value Symbol's Name + Addend
> 0000000000000000 0000003f00000001 R_X86_64_64 0000000000000000 homonym_string + 0
> 0000000000000008 0000004900000001 R_X86_64_64 0000000000000000 get_homonym_string + 0
>
> for which klp-convert looks up in symbols.klp:
>
> klp-convert-symbol-data.0.2
> *vmlinux
> ...
> *test_klp_convert_mod
> -test_klp_convert_mod_a.c << added filenames to the format
> test_klp_get_driver_name
> driver_name
> get_homonym_string << sympos = 1
> homonym_string << sympos = 1
> ...
> -test_klp_convert_mod_b.c
> get_homonym_string << sympos = 2
> homonym_string << sympos = 2
> ...
>
> and then generates the usual klp-relocations as currently defined.
This can get verbose very quickly, but I liked the idea. The sympos is much more
cryptic than specifying the file where the symbol lives on.
>
> (Unfortunately full pathnames are not saved in the STT_FILE symbol table
> entries, so there will be a few non-unique <obj,file,symbol> entries. I
> believe the last time this was discussed, we found that there were a
> relatively small number of such symbols.)
>
> Have you tried retrofitting klp-convert into any real-world livepatch?
> I'm curious as to your observations on the overall experience, or
> thoughts on the sympos annotation style noted above.
As I mentioned I'll start using klp-convert with new livepaches for testing
purposes in the next coming weeks. I'll reply in a few weeks about the
experience so far.
>
> Regards,
>
> -- Joe
>
next prev parent reply other threads:[~2023-03-20 20:15 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 14:08 [PATCH v7 00/10] livepatch: klp-convert tool Joe Lawrence
2023-03-06 14:08 ` [PATCH v7 01/10] livepatch: Create and include UAPI headers Joe Lawrence
2023-03-07 11:41 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 02/10] livepatch: Add klp-convert tool Joe Lawrence
2023-03-14 18:26 ` Marcos Paulo de Souza
2023-03-17 20:06 ` Joe Lawrence
2023-03-20 19:53 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 03/10] kbuild/modpost: create symbols.klp and integrate klp-convert Joe Lawrence
2023-03-14 18:48 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 04/10] livepatch: Add sample livepatch module Joe Lawrence
2023-03-14 18:17 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 05/10] documentation: Update on livepatch elf format Joe Lawrence
2023-03-07 11:48 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 06/10] livepatch/selftests: add klp-convert Joe Lawrence
2023-03-14 20:22 ` Marcos Paulo de Souza
2023-03-06 14:08 ` [PATCH v7 07/10] livepatch/selftests: test multiple sections Joe Lawrence
2023-03-06 14:08 ` [PATCH v7 08/10] livepatch/selftests: add __asm__ symbol renaming examples Joe Lawrence
2023-03-06 14:08 ` [PATCH v7 09/10] livepatch/selftests: add data relocations test Joe Lawrence
2023-03-06 14:08 ` [PATCH v7 10/10] livepatch/selftests: add static keys test Joe Lawrence
2023-03-14 20:23 ` [PATCH v7 00/10] livepatch: klp-convert tool Marcos Paulo de Souza
2023-03-17 20:29 ` Joe Lawrence
2023-03-17 23:20 ` Josh Poimboeuf
2023-03-20 19:23 ` Joe Lawrence
2023-04-11 10:06 ` Nicolai Stange
2023-05-02 23:38 ` Marcos Paulo de Souza
2023-05-03 19:54 ` Joe Lawrence
2023-05-09 20:34 ` Marcos Paulo de Souza
2023-03-20 20:15 ` Marcos Paulo de Souza [this message]
2023-04-19 20:27 ` Marcos Paulo de Souza
2023-03-30 12:10 Alexey Dobriyan
2023-03-30 17:04 ` Alexey Dobriyan
2023-03-31 16:03 ` Joe Lawrence
2023-04-01 9:59 ` Alexey Dobriyan
2023-03-31 15:58 ` Joe Lawrence
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