lkml.org 
[lkml]   [2019]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 0/9] klp-convert livepatch build tooling
On Wed, Apr 10, 2019 at 11:50:49AM -0400, Joe Lawrence wrote:
> Hi folks,
>
> This is the third installment of the klp-convert tool for generating and
> processing livepatch symbols for livepatch module builds. For those
> following along at home, archive links to previous versions:
>
> RFC:
> https://lore.kernel.org/lkml/cover.1477578530.git.jpoimboe@redhat.com/
> v2:
> https://lore.kernel.org/lkml/f52d29f7-7d1b-ad3d-050b-a9fa8878faf2@redhat.com/
>
> (Note that I don't see v2 archived at lore, but that is a link to the
> most recent subthread that lore did catch.)
>
>
> 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
> Symbols.list 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.
>
>
> Branches
> --------
>
> Since I spent some time tinkering with v2 and accumulated a bunch of
> fixes, I collected them up and am posting this new version. For review
> purposes, I posted two branches up to github:
>
> 1 - an expanded branch that with changes separate from the original
> https://github.com/joe-lawrence/linux/commits/klp-convert-v3-expanded
>
> 2 - a squashed branch of (1) that comprises v3:
> https://github.com/joe-lawrence/linux/commits/klp-convert-v3
>
> Non-trivial commits in the expanded branch have some extra commentary
> and details for debugging in the commit message that were dropped when
> squashing into their respective parent commits.
>
>
> TODO
> ----
>
> There are a few outstanding items that I came across while reviewing v2,
> but as changes started accumulating, it made sense to defer those to a
> later version. I'll reply to this thread individual topics to start
> discussion sub-threads for those.
>
>
> Changelogs
> ----------
>
> The commit changelogs were getting long, so I've moved them here for
> posterity and review purposes:
>
> livepatch: Create and include UAPI headers
> v2:
> - jmoreira: split up and changelog
> v3:
> - joe: convert to SPDX license tags
>
> kbuild: Support for Symbols.list creation
> v3:
> - jmoreira: adjust for multiobject livepatch
> - joe: add klpclean to PHONY
> - joe: align KLP prefix
>
> livepatch: Add klp-convert tool
> v2:
> - khlebnikov: use HOSTLOADLIBES_ instead of HOSTLDFLAGS: -lelf must be
> at the end
> - jmoreira: add support to automatic relocation conversion in
> klp-convert.c, changelog
> v3:
> - joe: convert to SPDX license tags
> - jmoreira: add rela symbol name to WARNs
> - jmoreira: ignore relocations to .TOC and symbols with index 0
> - joe: separate and fix valid_sympos() sympos=0 and sympos=1..n checks
> - joe: fix symbol use-after-frees
> - joe: fix remaining valgrind leak complaints (non-error paths only)
> - joe: checkpatch nits
>
> livepatch: Add klp-convert annotation helpers
> v2:
> - jmoreira: split up: move KLP_MODULE_RELOC from previous patch to
> here, add KLP_SYMPOS, move macros from include/uapi/livepatch.h to
> include/linux/livepatch.h
> v3:
> - joe: suggested by jpoimboe, KLP_MODULE_RELOC macro should 4-byte
> align klp_module_reloc structures
>
> modpost: Integrate klp-convert
> v2:
> - khlebnikov: save cmd_ld_ko_o into .module.cmd, if_changed_rule
> doesn't do that.f
> - khlebnikov: fix bashisms for debian where /bin/sh is a symlink to
> /bin/dash
> - khlebnikov: rename rule_link_module to rule_ld_ko_o, otherwise
> arg-check inside if_changed_rule compares cmd_link_module and
> cmd_ld_ko_o.
> - khlebnikov: check modinfo -F livepatch only if CONFIG_LIVEPATCH is
> true.
> - mbenes: remove modinfo call. LIVEPATCH_ in Makefile
> - jmoreira: split up: move the .livepatch file-based scheme for
> identifying livepatches to a previous patch, as it was required for
> correctly building Symbols.list there.
> v3:
> - joe: adjust rule_ld_ko_o to call echo-cmd
> - joe: rebase for v5.1
> - joe: align KLP prefix
>
> modpost: Add modinfo flag to livepatch modules
> v2:
> - jmoreira: fix modpost.c (add_livepatch_flag) to update module
> structure with livepatch flag and prevent modpost from breaking due to
> unresolved symbols
> v3:
> - joe: adjust modpost.c::get_modinfo() call for v5.0 version
>
> livepatch: Add sample livepatch module
> v3:
> - joe: update all in-tree livepatches with LIVEPATCH_* modinfo flag
>
> documentation: Update on livepatch elf format
> v2:
> - jmoreira: update module to use KLP_SYMPOS
> - jmoreira: Comments on symbol resolution scheme
> - jmoreira: Update Makefile
> - jmoreira: Remove MODULE_INFO statement
> - jmoreira: Changelog
> v3:
> - joe: rebase for v5.1
> - joe: code shuffle to better match original source file
>
> livepatch/selftests: add klp-convert
> v3:
> - joe: clarify sympos=0 and sympos=1..n
>
>
> And now the usual git cover-letter boilerplate...
>
> Joao Moreira (2):
> kbuild: Support for Symbols.list creation
> documentation: Update on livepatch elf format
>
> Joe Lawrence (1):
> livepatch/selftests: add klp-convert
>
> Josh Poimboeuf (5):
> livepatch: Create and include UAPI headers
> livepatch: Add klp-convert tool
> livepatch: Add klp-convert annotation helpers
> modpost: Integrate klp-convert
> livepatch: Add sample livepatch module
>
> Miroslav Benes (1):
> modpost: Add modinfo flag to livepatch modules
>
> .gitignore | 1 +
> Documentation/livepatch/livepatch.txt | 3 +
> Documentation/livepatch/module-elf-format.txt | 50 +-
> MAINTAINERS | 2 +
> Makefile | 30 +-
> include/linux/livepatch.h | 13 +
> include/uapi/linux/livepatch.h | 22 +
> kernel/livepatch/core.c | 4 +-
> lib/livepatch/Makefile | 15 +
> lib/livepatch/test_klp_atomic_replace.c | 1 -
> lib/livepatch/test_klp_callbacks_demo.c | 1 -
> lib/livepatch/test_klp_callbacks_demo2.c | 1 -
> lib/livepatch/test_klp_convert1.c | 106 +++
> lib/livepatch/test_klp_convert2.c | 103 +++
> lib/livepatch/test_klp_convert_mod_a.c | 25 +
> lib/livepatch/test_klp_convert_mod_b.c | 13 +
> lib/livepatch/test_klp_livepatch.c | 1 -
> samples/livepatch/Makefile | 7 +
> .../livepatch/livepatch-annotated-sample.c | 102 +++
> samples/livepatch/livepatch-sample.c | 1 -
> scripts/Kbuild.include | 4 +-
> scripts/Makefile | 1 +
> scripts/Makefile.build | 7 +
> scripts/Makefile.modpost | 24 +-
> scripts/livepatch/.gitignore | 1 +
> scripts/livepatch/Makefile | 7 +
> scripts/livepatch/elf.c | 753 ++++++++++++++++++
> scripts/livepatch/elf.h | 72 ++
> scripts/livepatch/klp-convert.c | 692 ++++++++++++++++
> scripts/livepatch/klp-convert.h | 39 +
> scripts/livepatch/list.h | 391 +++++++++
> scripts/mod/modpost.c | 82 +-
> scripts/mod/modpost.h | 1 +
> .../selftests/livepatch/test-livepatch.sh | 64 ++
> 34 files changed, 2616 insertions(+), 23 deletions(-)
> create mode 100644 include/uapi/linux/livepatch.h
> create mode 100644 lib/livepatch/test_klp_convert1.c
> create mode 100644 lib/livepatch/test_klp_convert2.c
> create mode 100644 lib/livepatch/test_klp_convert_mod_a.c
> create mode 100644 lib/livepatch/test_klp_convert_mod_b.c
> create mode 100644 samples/livepatch/livepatch-annotated-sample.c
> create mode 100644 scripts/livepatch/.gitignore
> create mode 100644 scripts/livepatch/Makefile
> create mode 100644 scripts/livepatch/elf.c
> create mode 100644 scripts/livepatch/elf.h
> create mode 100644 scripts/livepatch/klp-convert.c
> create mode 100644 scripts/livepatch/klp-convert.h
> create mode 100644 scripts/livepatch/list.h
>
> --
> 2.20.1

[ cc += Jason and Evgenii ]

Apologies for the long brain dump, but I promised to reply to this
thread with some of the larger TODO issues I came across with this
patchset. Static key support is probably the most complicated item, so
there is a lot of debugging output I can provide.

See the tl;dr and Future Work sections for the executive summary.


Static key support
==================

tl;dr
-----

Livepatch symbols are created when building livepatch modules that
reference the (non-exported) static keys of a target object.

When loading a livepatch that contains klp-converted static key symbols,
the module loader crashes.


Testing setup
-------------

The easiest way to see the source and repro is to grab this branch:

https://github.com/joe-lawrence/linux/commits/klp-convert-v4-static-keys

and note these last two commits:

- livepatch/klp-convert: abort on static key conversion: this will
prevent klp-convert from converting any relocations to the
__jump_table. Revert this commit to see the crash. If we don't
have a fix before merging, I would suggest a temporary abort
like this to avoid silently creating dangerous livepatches.

- livepatch/selftests: add livepatch static keys: this adds the
self-test which will repro the crash.


I added a new livepatch selftest to verify klp-convert and static key
behavior: it consists of two kernel modules: test_klp_static_keys_mod.ko
and livepatch module that patches it, test_klp_static_keys.ko.

The base module contains a few different types of static keys: default
true / false, exported / not-exported, and one created by the trace
event macro infrastructure.

The livepatch module references each of these, relying upon klp-convert.
This module also provides its own static key for reference.

test_klp_static_keys_mod.ko
---------------------------
module_key (false) - exported
module_key2 (true) <----
TRACE_EVENT(test_klp_static_keys) <-- |
| |
| | klp-convert resolves
test_klp_static_keys.ko - livepatch | | these references
----------------------------------- | |
klp_key (true) | |
test_klp_static_keys ----------------- |
module_key2 ----------------------------
module_key


Currently .klp symbols are created as well as a relocation section for those
symbols in the their corresponding .text locations.


test_klp_static_keys_mod.ko
---------------------------

% eu-readelf --symbols lib/livepatch/test_klp_static_keys_mod.ko | \
grep -e '__tracepoint_test_klp_static_keys' -e '\<module_key[2]*\>'

49: 0000000000000010 16 OBJECT LOCAL DEFAULT 44 module_key
65: 0000000000000010 16 OBJECT LOCAL DEFAULT 32 module_key2
96: 0000000000000000 48 OBJECT GLOBAL DEFAULT 40 __tracepoint_test_klp_static_keys


test_klp_static_keys.klp.o
--------------------------

% eu-readelf --symbols lib/livepatch/test_klp_static_keys.klp.o | \
grep -e '__tracepoint_test_klp_static_keys' -e '\<module_key[2]*\>'

71: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UNDEF __tracepoint_test_klp_static_keys
78: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UNDEF module_key2
84: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UNDEF module_key

Lots of __tracepoint_test_klp_static_keys relocations since each
module function registers an event when it is called:

% eu-readelf --reloc lib/livepatch/test_klp_static_keys.klp.o
Relocation section [ 4] '.rela.text' for section [ 3] '.text' at offset 0x2e7d8 contains 88 entries:
Offset Type Value Addend Name
...
0x000000000000002c X86_64_32S 000000000000000000 +0 module_key2
...
0x000000000000007c X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x00000000000000d9 X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x0000000000000169 X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x00000000000001f9 X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x000000000000028c X86_64_32S 000000000000000000 +0 module_key
...
0x00000000000002dc X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x000000000000038c X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys
...
0x00000000000003eb X86_64_PC32 000000000000000000 +36 __tracepoint_test_klp_static_keys


Relocations generated for the __jump_table itself, note that I grouped
each jump entry <code, target, key> relocation set:

Relocation section [19] '.rela__jump_table' for section [18] '__jump_table' at offset 0x2fb28 contains 30 entries:
Offset Type Value Addend Name
000000000000000000 X86_64_PC32 000000000000000000 +12 .text
0x0000000000000004 X86_64_PC32 000000000000000000 +102 .text
0x0000000000000008 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000010 X86_64_PC32 000000000000000000 +188 .text
0x0000000000000014 X86_64_PC32 000000000000000000 +195 .text
0x0000000000000018 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000020 X86_64_PC32 000000000000000000 +304 .text
0x0000000000000024 X86_64_PC32 000000000000000000 +0 .text.unlikely
0x0000000000000028 X86_64_PC64 000000000000000000 +16 .bss

0x0000000000000030 X86_64_PC32 000000000000000000 +332 .text
0x0000000000000034 X86_64_PC32 000000000000000000 +339 .text
0x0000000000000038 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000040 X86_64_PC32 000000000000000000 +448 .text
0x0000000000000044 X86_64_PC32 000000000000000000 +52 .text.unlikely
0x0000000000000048 X86_64_PC64 000000000000000000 +0 module_key

0x0000000000000050 X86_64_PC32 000000000000000000 +476 .text
0x0000000000000054 X86_64_PC32 000000000000000000 +483 .text
0x0000000000000058 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000060 X86_64_PC32 000000000000000000 +592 .text
0x0000000000000064 X86_64_PC32 000000000000000000 +104 .text.unlikely
0x0000000000000068 X86_64_PC64 000000000000000000 +1 module_key2

0x0000000000000070 X86_64_PC32 000000000000000000 +620 .text
0x0000000000000074 X86_64_PC32 000000000000000000 +710 .text
0x0000000000000078 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000080 X86_64_PC32 000000000000000000 +796 .text
0x0000000000000084 X86_64_PC32 000000000000000000 +886 .text
0x0000000000000088 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys

0x0000000000000090 X86_64_PC32 000000000000000000 +962 .text
0x0000000000000094 X86_64_PC32 000000000000000000 +981 .text
0x0000000000000098 X86_64_PC64 000000000000000000 +8 __tracepoint_test_klp_static_keys


test_klp_static_keys.ko
-----------------------

Finally klp-convert has transformed a bunch of symbols for us:

% eu-readelf --symbols lib/livepatch/test_klp_static_keys.ko | \
grep -e '__tracepoint_test_klp_static_keys' -e '\<module_key[2]*\>'

71: 0000000000000000 0 NOTYPE GLOBAL DEFAULT LOOS+0 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
78: 0000000000000000 0 NOTYPE GLOBAL DEFAULT LOOS+0 .klp.sym.test_klp_static_keys_mod.module_key2,0
84: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UNDEF module_key

% eu-readelf --reloc lib/livepatch/test_klp_static_keys.ko

Relocation section [19] '.rela__jump_table' for section [18] '__jump_table' at offset 0x2480 contains 30 entries:
Offset Type Value Addend Name
000000000000000000 X86_64_PC32 000000000000000000 +12 .text
0x0000000000000004 X86_64_PC32 000000000000000000 +102 .text
0x0000000000000008 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000010 X86_64_PC32 000000000000000000 +188 .text
0x0000000000000014 X86_64_PC32 000000000000000000 +195 .text
0x0000000000000018 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000020 X86_64_PC32 000000000000000000 +304 .text
0x0000000000000024 X86_64_PC32 000000000000000000 +0 .text.unlikely
0x0000000000000028 X86_64_PC64 000000000000000000 +16 .bss

0x0000000000000030 X86_64_PC32 000000000000000000 +332 .text
0x0000000000000034 X86_64_PC32 000000000000000000 +339 .text
0x0000000000000038 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000040 X86_64_PC32 000000000000000000 +448 .text
0x0000000000000044 X86_64_PC32 000000000000000000 +52 .text.unlikely
0x0000000000000048 X86_64_PC64 000000000000000000 +0 module_key

0x0000000000000050 X86_64_PC32 000000000000000000 +476 .text
0x0000000000000054 X86_64_PC32 000000000000000000 +483 .text
0x0000000000000058 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000060 X86_64_PC32 000000000000000000 +592 .text
0x0000000000000064 X86_64_PC32 000000000000000000 +104 .text.unlikely
0x0000000000000068 X86_64_PC64 000000000000000000 +1 .klp.sym.test_klp_static_keys_mod.module_key2,0

0x0000000000000070 X86_64_PC32 000000000000000000 +620 .text
0x0000000000000074 X86_64_PC32 000000000000000000 +710 .text
0x0000000000000078 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000080 X86_64_PC32 000000000000000000 +796 .text
0x0000000000000084 X86_64_PC32 000000000000000000 +886 .text
0x0000000000000088 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

0x0000000000000090 X86_64_PC32 000000000000000000 +962 .text
0x0000000000000094 X86_64_PC32 000000000000000000 +981 .text
0x0000000000000098 X86_64_PC64 000000000000000000 +8 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0

And here's our final set of klp-converted relocations which include the
unexported trace point symbol and module_key2 symbols:

Relocation section [44] '.klp.rela.test_klp_static_keys_mod..text' for section [ 3] '.text' at offset 0x55c18 contains 12 entries:
Offset Type Value Addend Name
...
0x00000000000003eb X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x000000000000038c X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x00000000000002dc X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x00000000000001f9 X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x0000000000000169 X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x00000000000000d9 X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x000000000000007c X86_64_PC32 000000000000000000 +36 .klp.sym.test_klp_static_keys_mod.__tracepoint_test_klp_static_keys,0
0x000000000000002c X86_64_32S 000000000000000000 +0 .klp.sym.test_klp_static_keys_mod.module_key2,0
...


Current behavior
----------------

Not good. The livepatch successfully builds but crashes on load:

% insmod lib/livepatch/test_klp_static_keys_mod.ko
% insmod lib/livepatch/test_klp_static_keys.ko

BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
#PF error: [normal kernel read fault]
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
CPU: 3 PID: 9367 Comm: insmod Tainted: G E K 5.1.0-rc4+ #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20180724_192412-buildhw-07.phx2.fedoraproject.org-1.fc29 04/01/2014
RIP: 0010:jump_label_apply_nops+0x3b/0x60
Code: 02 00 00 48 c1 e5 04 48 01 dd 48 39 eb 74 3a 72 0b eb 36 48 83 c3 10 48 39 dd 76 2d 48 8b 43 08 48 89 c2 83 e0 01 48 83 e2 fc <48> 8b 54 13 10 83 e2 01 38 c2 75 dd 48 89 df 31 f6 48 83 c3 10 e8
RSP: 0018:ffffa8874068fcf8 EFLAGS: 00010206
RAX: 0000000000000000 RBX: ffffffffc07fd000 RCX: 000000000000000d
RDX: 000000003f803000 RSI: ffffffffa5077be0 RDI: ffffffffc07fe540
RBP: ffffffffc07fd0a0 R08: ffffa88740f43878 R09: ffffa88740eed000
R10: 0000000000055a4b R11: ffffa88740f43878 R12: ffffa88740f430b8
R13: 0000000000000000 R14: ffffa88740f42df8 R15: 0000000000042b01
FS: 00007f4f1dafb740(0000) GS:ffff9a81fbb80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000010 CR3: 00000000b5d8a000 CR4: 00000000000006e0
Call Trace:
module_finalize+0x184/0x1c0
load_module+0x1400/0x1910
? kernel_read_file+0x18d/0x1c0
? __do_sys_finit_module+0xa8/0x110
__do_sys_finit_module+0xa8/0x110
do_syscall_64+0x55/0x1a0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f4f1cae82bd


Future work
-----------

At the very least, I think this call-chain ordering is wrong for
livepatch static key symbols:

load_module

apply_relocations

post_relocation
module_finalize
jump_label_apply_nops <<

...

prepare_coming_module
blocking_notifier_call_chain(&module_notify_list, MODULE_STATE_COMING, mod);
jump_label_module_notify
case MODULE_STATE_COMING
jump_label_add_module <<

do_init_module

do_one_initcall(mod->init)
__init patch_init [kpatch-patch]
klp_register_patch
klp_init_patch
klp_for_each_object(patch, obj)
klp_init_object
klp_init_object_loaded
klp_write_object_relocations <<

blocking_notifier_call_chain(&module_notify_list, MODULE_STATE_LIVE, mod);
jump_label_module_notify
case MODULE_STATE_LIVE
jump_label_invalidate_module_init

where klp_write_object_relocations() is called way *after*
jump_label_apply_nops() and jump_label_add_module().


Detection
---------

I have been tinkering with some prototype code to defer
jump_label_apply_nops() and jump_label_add_module(), but it has been
slow going. I think the jist of it is that we're going to need to call
these dynamically when individual klp_objects are patched, not when the
livepatch module itself loads. If anyone with static key expertise
wants to jump in here, let me know.

In the meantime, I cooked up a potential followup commit to detect
conversion of static key symbols and klp-convert failure. It basically
runs through the output .ko's ELF symbols and verifies that none of the
converted ones can be found as a .rela__jump_table relocated symbol. It
accurately catches the problematic references in test_klp_static_keys.ko
thus far.

This was based on a similar issue reported as a bug against
kpatch-build, in which Josh wrote code to detect this scenario:

https://github.com/dynup/kpatch/issues/946
https://github.com/jpoimboe/kpatch/commit/2cd2d27607566aee9590c367e615207ce1ce24c6

I can post ("livepatch/klp-convert: abort on static key conversion")
here as a follow commit if it looks reasonable and folks wish to review
it... or we can try and tackle static keys before merging klp-convert.


-- Joe

\
 
 \ /
  Last update: 2019-04-12 23:28    [W:0.374 / U:11.348 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site