linux-toradex.git/kernel/livepatch, branch v6.19

livepatch: Fix having __klp_objects relics in non-livepatch modules

2026-02-05T16:00:44+00:00

The linker script scripts/module.lds.S specifies that all input
__klp_objects sections should be consolidated into an output section of
the same name, and start/stop symbols should be created to enable
scripts/livepatch/init.c to locate this data.

This start/stop pattern is not ideal for modules because the symbols are
created even if no __klp_objects input sections are present.
Consequently, a dummy __klp_objects section also appears in the
resulting module. This unnecessarily pollutes non-livepatch modules.

Instead, since modules are relocatable files, the usual method for
locating consolidated data in a module is to read its section table.
This approach avoids the aforementioned problem.

The klp_modinfo already stores a copy of the entire section table with
the final addresses. Introduce a helper function that
scripts/livepatch/init.c can call to obtain the location of the
__klp_objects section from this data.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Signed-off-by: Petr Pavlu 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Reviewed-by: Aaron Tomlin 
Link: https://patch.msgid.link/20260123102825.3521961-2-petr.pavlu@suse.com
Signed-off-by: Josh Poimboeuf

Merge tag 'livepatching-for-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching

2025-12-03T21:46:48+00:00

Pull livepatching updates from Petr Mladek:

 - Support both paths where tracefs is typically mounted in selftests

 - Make old_sympos 0 and 1 equal. They both are valid when there is only
   one symbol with the given name.

* tag 'livepatching-for-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching:
  selftests: livepatch: use canonical ftrace path
  livepatch: Match old_sympos 0 and 1 in klp_find_func()

livepatch: Match old_sympos 0 and 1 in klp_find_func()

2025-10-15T12:47:19+00:00

When there is only one function of the same name, old_sympos of 0 and 1
are logically identical. Match them in klp_find_func().

This is to avoid a corner case with different toolchain behavior.

In this specific issue, two versions of kpatch-build were used to
build livepatch for the same kernel. One assigns old_sympos == 0 for
unique local functions, the other assigns old_sympos == 1 for unique
local functions. Both versions work fine by themselves. (PS: This
behavior change was introduced in a downstream version of kpatch-build.
This change does not exist in upstream kpatch-build.)

However, during livepatch upgrade (with the replace flag set) from a
patch built with one version of kpatch-build to the same fix built with
the other version of kpatch-build, livepatching fails with errors like:

[   14.218706] sysfs: cannot create duplicate filename 'xxx/somefunc,1'
...
[   14.219466] Call Trace:
[   14.219468]  
[   14.219469]  dump_stack_lvl+0x47/0x60
[   14.219474]  sysfs_warn_dup.cold+0x17/0x27
[   14.219476]  sysfs_create_dir_ns+0x95/0xb0
[   14.219479]  kobject_add_internal+0x9e/0x260
[   14.219483]  kobject_add+0x68/0x80
[   14.219485]  ? kstrdup+0x3c/0xa0
[   14.219486]  klp_enable_patch+0x320/0x830
[   14.219488]  patch_init+0x443/0x1000 [ccc_0_6]
[   14.219491]  ? 0xffffffffa05eb000
[   14.219492]  do_one_initcall+0x2e/0x190
[   14.219494]  do_init_module+0x67/0x270
[   14.219496]  init_module_from_file+0x75/0xa0
[   14.219499]  idempotent_init_module+0x15a/0x240
[   14.219501]  __x64_sys_finit_module+0x61/0xc0
[   14.219503]  do_syscall_64+0x5b/0x160
[   14.219505]  entry_SYSCALL_64_after_hwframe+0x4b/0x53
[   14.219507] RIP: 0033:0x7f545a4bd96d
...
[   14.219516] kobject: kobject_add_internal failed for somefunc,1 with
    -EEXIST, don't try to register things with the same name ...

This happens because klp_find_func() thinks somefunc with old_sympos==0
is not the same as somefunc with old_sympos==1, and klp_add_object_nops
adds another xxx/func,1 to the list of functions to patch.

Signed-off-by: Song Liu 
Acked-by: Josh Poimboeuf 
[pmladek@suse.com: Fixed some typos.]
Reviewed-by: Petr Mladek 
Tested-by: Petr Mladek 
Signed-off-by: Petr Mladek

livepatch: Add CONFIG_KLP_BUILD

2025-10-14T21:50:18+00:00

In preparation for introducing klp-build, add a new CONFIG_KLP_BUILD
option.  The initial version will only be supported on x86-64.

Acked-by: Petr Mladek 
Tested-by: Joe Lawrence 
Signed-off-by: Josh Poimboeuf

objtool/klp: Introduce klp diff subcommand for diffing object files

2025-10-14T21:50:18+00:00

Add a new klp diff subcommand which performs a binary diff between two
object files and extracts changed functions into a new object which can
then be linked into a livepatch module.

This builds on concepts from the longstanding out-of-tree kpatch [1]
project which began in 2012 and has been used for many years to generate
livepatch modules for production kernels.  However, this is a complete
rewrite which incorporates hard-earned lessons from 12+ years of
maintaining kpatch.

Key improvements compared to kpatch-build:

  - Integrated with objtool: Leverages objtool's existing control-flow
    graph analysis to help detect changed functions.

  - Works on vmlinux.o: Supports late-linked objects, making it
    compatible with LTO, IBT, and similar.

  - Simplified code base: ~3k fewer lines of code.

  - Upstream: No more out-of-tree #ifdef hacks, far less cruft.

  - Cleaner internals: Vastly simplified logic for symbol/section/reloc
    inclusion and special section extraction.

  - Robust __LINE__ macro handling: Avoids false positive binary diffs
    caused by the __LINE__ macro by introducing a fix-patch-lines script
    (coming in a later patch) which injects #line directives into the
    source .patch to preserve the original line numbers at compile time.

Note the end result of this subcommand is not yet functionally complete.
Livepatch needs some ELF magic which linkers don't like:

  - Two relocation sections (.rela*, .klp.rela*) for the same text
    section.

  - Use of SHN_LIVEPATCH to mark livepatch symbols.

Unfortunately linkers tend to mangle such things.  To work around that,
klp diff generates a linker-compliant intermediate binary which encodes
the relevant KLP section/reloc/symbol metadata.

After module linking, a klp post-link step (coming soon) will clean up
the mess and convert the linked .ko into a fully compliant livepatch
module.

Note this subcommand requires the diffed binaries to have been compiled
with -ffunction-sections and -fdata-sections, and processed with
'objtool --checksum'.  Those constraints will be handled by a klp-build
script introduced in a later patch.

Without '-ffunction-sections -fdata-sections', reliable object diffing
would be infeasible due to toolchain limitations:

  - For intra-file+intra-section references, the compiler might
    occasionally generated hard-coded instruction offsets instead of
    relocations.

  - Section-symbol-based references can be ambiguous:

    - Overlapping or zero-length symbols create ambiguity as to which
      symbol is being referenced.

    - A reference to the end of a symbol (e.g., checking array bounds)
      can be misinterpreted as a reference to the next symbol, or vice
      versa.

A potential future alternative to '-ffunction-sections -fdata-sections'
would be to introduce a toolchain option that forces symbol-based
(non-section) relocations.

Acked-by: Petr Mladek 
Tested-by: Joe Lawrence 
Signed-off-by: Josh Poimboeuf

x86/module: Improve relocation error messages

2025-10-14T21:45:21+00:00

Add the section number and reloc index to relocation error messages to
help find the faulty relocation.

Acked-by: Petr Mladek 
Tested-by: Joe Lawrence 
Signed-off-by: Josh Poimboeuf

sched,livepatch: Untangle cond_resched() and live-patching

2025-05-14T11:16:24+00:00

With the goal of deprecating / removing VOLUNTARY preempt, live-patch
needs to stop relying on cond_resched() to make forward progress.

Instead, rely on schedule() with TASK_FREEZABLE set. Just like
live-patching, the freezer needs to be able to stop tasks in a safe /
known state.

[bigeasy: use likely() in __klp_sched_try_switch() and update comments]

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Reviewed-by: Petr Mladek 
Tested-by: Petr Mladek 
Tested-by: Miroslav Benes 
Acked-by: Miroslav Benes 
Acked-by: Josh Poimboeuf 
Link: https://lore.kernel.org/r/20250509113659.wkP_HJ5z@linutronix.de

Merge tag 'modules-6.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/modules/linux

2025-03-30T22:44:36+00:00

Pull modules updates from Petr Pavlu:

 - Use RCU instead of RCU-sched

   The mix of rcu_read_lock(), rcu_read_lock_sched() and
   preempt_disable() in the module code and its users has
   been replaced with just rcu_read_lock()

 - The rest of changes are smaller fixes and updates

* tag 'modules-6.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/modules/linux: (32 commits)
  MAINTAINERS: Update the MODULE SUPPORT section
  module: Remove unnecessary size argument when calling strscpy()
  module: Replace deprecated strncpy() with strscpy()
  params: Annotate struct module_param_attrs with __counted_by()
  bug: Use RCU instead RCU-sched to protect module_bug_list.
  static_call: Use RCU in all users of __module_text_address().
  kprobes: Use RCU in all users of __module_text_address().
  bpf: Use RCU in all users of __module_text_address().
  jump_label: Use RCU in all users of __module_text_address().
  jump_label: Use RCU in all users of __module_address().
  x86: Use RCU in all users of __module_address().
  cfi: Use RCU while invoking __module_address().
  powerpc/ftrace: Use RCU in all users of __module_text_address().
  LoongArch: ftrace: Use RCU in all users of __module_text_address().
  LoongArch/orc: Use RCU in all users of __module_address().
  arm64: module: Use RCU in all users of __module_text_address().
  ARM: module: Use RCU in all users of __module_text_address().
  module: Use RCU in all users of __module_text_address().
  module: Use RCU in all users of __module_address().
  module: Use RCU in search_module_extables().
  ...

module: Use RCU in find_module_all().

2025-03-10T10:54:44+00:00

The modules list and module::kallsyms can be accessed under RCU
assumption.

Remove module_assert_mutex_or_preempt() from find_module_all() so it can
be used under RCU protection without warnings. Update its callers to use
RCU protection instead of preempt_disable().

Cc: Jiri Kosina 
Cc: Joe Lawrence 
Cc: Josh Poimboeuf 
Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Miroslav Benes 
Cc: Petr Mladek 
Cc: Steven Rostedt 
Cc: linux-trace-kernel@vger.kernel.org
Cc: live-patching@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior 
Acked-by: Peter Zijlstra (Intel) 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20250108090457.512198-7-bigeasy@linutronix.de
Signed-off-by: Petr Pavlu

livepatch: Add comment to clarify klp_add_nops()

2025-03-04T14:59:07+00:00

Add detailed comments to clarify the purpose of klp_add_nops() function.
These comments are based on Petr's explanation[0].

Link: https://lore.kernel.org/all/Z6XUA7D0eU_YDMVp@pathway.suse.cz/ [0]
Suggested-by: Petr Mladek 
Suggested-by: Josh Poimboeuf 
Signed-off-by: Yafang Shao 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20250227024733.16989-2-laoar.shao@gmail.com
Signed-off-by: Petr Mladek