linux-toradex.git/kernel/livepatch/core.c, branch v5.12-rc5

kallsyms: refactor {,module_}kallsyms_on_each_symbol

2021-02-08T11:22:08+00:00

Require an explicit call to module_kallsyms_on_each_symbol to look
for symbols in modules instead of the call from kallsyms_on_each_symbol,
and acquire module_mutex inside of module_kallsyms_on_each_symbol instead
of leaving that up to the caller.  Note that this slightly changes the
behavior for the livepatch code in that the symbols from vmlinux are not
iterated anymore if objname is set, but that actually is the desired
behavior in this case.

Reviewed-by: Petr Mladek 
Acked-by: Miroslav Benes 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Jessica Yu

module: use RCU to synchronize find_module

2021-02-08T11:21:40+00:00

Allow for a RCU-sched critical section around find_module, following
the lower level find_module_all helper, and switch the two callers
outside of module.c to use such a RCU-sched critical section instead
of module_mutex.

Reviewed-by: Petr Mladek 
Acked-by: Miroslav Benes 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Jessica Yu

livepatch: Make klp_apply_object_relocs static

2020-05-10T22:31:38+00:00

Fix the following sparse warning:

kernel/livepatch/core.c:748:5: warning: symbol 'klp_apply_object_relocs' was
not declared.

The klp_apply_object_relocs() has only one call site within core.c;
it should be static

Fixes: 7c8e2bdd5f0d ("livepatch: Apply vmlinux-specific KLP relocations early")
Reported-by: Hulk Robot 
Signed-off-by: Samuel Zou 
Acked-by: Josh Poimboeuf 
Signed-off-by: Jiri Kosina

x86/module: Use text_mutex in apply_relocate_add()

2020-05-07T22:12:43+00:00

Now that the livepatch code no longer needs the text_mutex for changing
module permissions, move its usage down to apply_relocate_add().

Note the s390 version of apply_relocate_add() doesn't need to use the
text_mutex because it already uses s390_kernel_write_lock, which
accomplishes the same task.

Signed-off-by: Josh Poimboeuf 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Signed-off-by: Jiri Kosina

livepatch: Remove module_disable_ro() usage

2020-05-07T22:12:43+00:00

With arch_klp_init_object_loaded() gone, and apply_relocate_add() now
using text_poke(), livepatch no longer needs to use module_disable_ro().

Signed-off-by: Josh Poimboeuf 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Signed-off-by: Jiri Kosina

livepatch: Prevent module-specific KLP rela sections from referencing vmlinux symbols

2020-05-07T22:12:42+00:00

Prevent module-specific KLP rela sections from referencing vmlinux
symbols.  This helps prevent ordering issues with module special section
initializations.  Presumably such symbols are exported and normal relas
can be used instead.

Suggested-by: Peter Zijlstra 
Signed-off-by: Josh Poimboeuf 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Signed-off-by: Jiri Kosina

livepatch: Remove .klp.arch

2020-05-07T22:12:42+00:00

After the previous patch, vmlinux-specific KLP relocations are now
applied early during KLP module load.  This means that .klp.arch
sections are no longer needed for *vmlinux-specific* KLP relocations.

One might think they're still needed for *module-specific* KLP
relocations.  If a to-be-patched module is loaded *after* its
corresponding KLP module is loaded, any corresponding KLP relocations
will be delayed until the to-be-patched module is loaded.  If any
special sections (.parainstructions, for example) rely on those
relocations, their initializations (apply_paravirt) need to be done
afterwards.  Thus the apparent need for arch_klp_init_object_loaded()
and its corresponding .klp.arch sections -- it allows some of the
special section initializations to be done at a later time.

But... if you look closer, that dependency between the special sections
and the module-specific KLP relocations doesn't actually exist in
reality.  Looking at the contents of the .altinstructions and
.parainstructions sections, there's not a realistic scenario in which a
KLP module's .altinstructions or .parainstructions section needs to
access a symbol in a to-be-patched module.  It might need to access a
local symbol or even a vmlinux symbol; but not another module's symbol.
When a special section needs to reference a local or vmlinux symbol, a
normal rela can be used instead of a KLP rela.

Since the special section initializations don't actually have any real
dependency on module-specific KLP relocations, .klp.arch and
arch_klp_init_object_loaded() no longer have a reason to exist.  So
remove them.

As Peter said much more succinctly:

  So the reason for .klp.arch was that .klp.rela.* stuff would overwrite
  paravirt instructions. If that happens you're doing it wrong. Those
  RELAs are core kernel, not module, and thus should've happened in
  .rela.* sections at patch-module loading time.

  Reverting this removes the two apply_{paravirt,alternatives}() calls
  from the late patching path, and means we don't have to worry about
  them when removing module_disable_ro().

[ jpoimboe: Rewrote patch description.  Tweaked klp_init_object_loaded()
	    error path. ]

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Josh Poimboeuf 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Signed-off-by: Jiri Kosina

livepatch: Apply vmlinux-specific KLP relocations early

2020-05-07T22:12:42+00:00

KLP relocations are livepatch-specific relocations which are applied to
a KLP module's text or data.  They exist for two reasons:

  1) Unexported symbols: replacement functions often need to access
     unexported symbols (e.g. static functions), which "normal"
     relocations don't allow.

  2) Late module patching: this is the ability for a KLP module to
     bypass normal module dependencies, such that the KLP module can be
     loaded *before* a to-be-patched module.  This means that
     relocations which need to access symbols in the to-be-patched
     module might need to be applied to the KLP module well after it has
     been loaded.

Non-late-patched KLP relocations are applied from the KLP module's init
function.  That usually works fine, unless the patched code wants to use
alternatives, paravirt patching, jump tables, or some other special
section which needs relocations.  Then we run into ordering issues and
crashes.

In order for those special sections to work properly, the KLP
relocations should be applied *before* the special section init code
runs, such as apply_paravirt(), apply_alternatives(), or
jump_label_apply_nops().

You might think the obvious solution would be to move the KLP relocation
initialization earlier, but it's not necessarily that simple.  The
problem is the above-mentioned late module patching, for which KLP
relocations can get applied well after the KLP module is loaded.

To "fix" this issue in the past, we created .klp.arch sections:

  .klp.arch.{module}..altinstructions
  .klp.arch.{module}..parainstructions

Those sections allow KLP late module patching code to call
apply_paravirt() and apply_alternatives() after the module-specific KLP
relocations (.klp.rela.{module}.{section}) have been applied.

But that has a lot of drawbacks, including code complexity, the need for
arch-specific code, and the (per-arch) danger that we missed some
special section -- for example the __jump_table section which is used
for jump labels.

It turns out there's a simpler and more functional approach.  There are
two kinds of KLP relocation sections:

  1) vmlinux-specific KLP relocation sections

     .klp.rela.vmlinux.{sec}

     These are relocations (applied to the KLP module) which reference
     unexported vmlinux symbols.

  2) module-specific KLP relocation sections

     .klp.rela.{module}.{sec}:

     These are relocations (applied to the KLP module) which reference
     unexported or exported module symbols.

Up until now, these have been treated the same.  However, they're
inherently different.

Because of late module patching, module-specific KLP relocations can be
applied very late, thus they can create the ordering headaches described
above.

But vmlinux-specific KLP relocations don't have that problem.  There's
nothing to prevent them from being applied earlier.  So apply them at
the same time as normal relocations, when the KLP module is being
loaded.

This means that for vmlinux-specific KLP relocations, we no longer have
any ordering issues.  vmlinux-referencing jump labels, alternatives, and
paravirt patching will work automatically, without the need for the
.klp.arch hacks.

All that said, for module-specific KLP relocations, the ordering
problems still exist and we *do* still need .klp.arch.  Or do we?  Stay
tuned.

Suggested-by: Peter Zijlstra 
Signed-off-by: Josh Poimboeuf 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Joe Lawrence 
Acked-by: Miroslav Benes 
Acked-by: Jessica Yu 
Signed-off-by: Jiri Kosina

livepatch: Disallow vmlinux.ko

2020-05-07T22:12:42+00:00

This is purely a theoretical issue, but if there were a module named
vmlinux.ko, the livepatch relocation code wouldn't be able to
distinguish between vmlinux-specific and vmlinux.o-specific KLP
relocations.

If CONFIG_LIVEPATCH is enabled, don't allow a module named vmlinux.ko.

Suggested-by: Peter Zijlstra 
Signed-off-by: Josh Poimboeuf 
Acked-by: Miroslav Benes 
Acked-by: Joe Lawrence 
Signed-off-by: Jiri Kosina

livepatch: Allow to distinguish different version of system state changes

2019-11-01T12:08:19+00:00

The atomic replace runs pre/post (un)install callbacks only from the new
livepatch. There are several reasons for this:

  + Simplicity: clear ordering of operations, no interactions between
	old and new callbacks.

  + Reliability: only new livepatch knows what changes can already be made
	by older livepatches and how to take over the state.

  + Testing: the atomic replace can be properly tested only when a newer
	livepatch is available. It might be too late to fix unwanted effect
	of callbacks from older	livepatches.

It might happen that an older change is not enough and the same system
state has to be modified another way. Different changes need to get
distinguished by a version number added to struct klp_state.

The version can also be used to prevent loading incompatible livepatches.
The check is done when the livepatch is enabled. The rules are:

  + Any completely new system state modification is allowed.

  + System state modifications with the same or higher version are allowed
    for already modified system states.

  + Cumulative livepatches must handle all system state modifications from
    already installed livepatches.

  + Non-cumulative livepatches are allowed to touch already modified
    system states.

Link: http://lkml.kernel.org/r/20191030154313.13263-4-pmladek@suse.com
To: Jiri Kosina 
Cc: Kamalesh Babulal 
Cc: Nicolai Stange 
Cc: live-patching@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Miroslav Benes 
Acked-by: Joe Lawrence 
Acked-by: Josh Poimboeuf 
Signed-off-by: Petr Mladek