linux.git/arch/powerpc/lib/code-patching.c, branch v4.19

powerpc/lib: fix book3s/32 boot failure due to code patching

2018-10-02T13:34:14+00:00

Commit 51c3c62b58b3 ("powerpc: Avoid code patching freed init
sections") accesses 'init_mem_is_free' flag too early, before the
kernel is relocated. This provokes early boot failure (before the
console is active).

As it is not necessary to do this verification that early, this
patch moves the test into patch_instruction() instead of
__patch_instruction().

This modification also has the advantage of avoiding unnecessary
remappings.

Fixes: 51c3c62b58b3 ("powerpc: Avoid code patching freed init sections")
Cc: stable@vger.kernel.org # 4.13+
Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman

powerpc: Avoid code patching freed init sections

2018-09-18T12:42:54+00:00

This stops us from doing code patching in init sections after they've
been freed.

In this chain:
  kvm_guest_init() ->
    kvm_use_magic_page() ->
      fault_in_pages_readable() ->
	 __get_user() ->
	   __get_user_nocheck() ->
	     barrier_nospec();

We have a code patching location at barrier_nospec() and
kvm_guest_init() is an init function. This whole chain gets inlined,
so when we free the init section (hence kvm_guest_init()), this code
goes away and hence should no longer be patched.

We seen this as userspace memory corruption when using a memory
checker while doing partition migration testing on powervm (this
starts the code patching post migration via
/sys/kernel/mobility/migration). In theory, it could also happen when
using /sys/kernel/debug/powerpc/barrier_nospec.

Cc: stable@vger.kernel.org # 4.13+
Signed-off-by: Michael Neuling 
Reviewed-by: Nicholas Piggin 
Reviewed-by: Christophe Leroy 
Signed-off-by: Michael Ellerman

powerpc/asm: Add a patch_site macro & helpers for patching instructions

2018-08-07T14:32:25+00:00

Add a macro and some helper C functions for patching single asm
instructions.

The gas macro means we can do something like:

  1:	nop
  	patch_site 1b, patch__foo

Which is less visually distracting than defining a GLOBAL symbol at 1,
and also doesn't pollute the symbol table which can confuse eg. perf.

These are obviously similar to our existing feature sections, but are
not automatically patched based on CPU/MMU features, rather they are
designed to be manually patched by C code at some arbitrary point.

Signed-off-by: Michael Ellerman

powerpc/lib/feature-fixups: use raw_patch_instruction()

2018-01-21T04:06:25+00:00

feature fixups need to use patch_instruction() early in the boot,
even before the code is relocated to its final address, requiring
patch_instruction() to use PTRRELOC() in order to address data.

But feature fixups applies on code before it is set to read only,
even for modules. Therefore, feature fixups can use
raw_patch_instruction() instead.

Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman

powerpc/lib/code-patching: refactor patch_instruction()

2018-01-21T04:06:25+00:00

patch_instruction() uses almost the same sequence as
__patch_instruction()

This patch refactor it so that patch_instruction() uses
__patch_instruction() instead of duplicating code.

Signed-off-by: Christophe Leroy 
Acked-by: Balbir Singh 
Signed-off-by: Michael Ellerman

powerpc/modules: Don't try to restore r2 after a sibling call

2017-12-11T02:03:29+00:00

When attempting to load a livepatch module, I got the following error:

  module_64: patch_module: Expect noop after relocate, got 3c820000

The error was triggered by the following code in
unregister_netdevice_queue():

  14c:   00 00 00 48     b       14c 
                         14c: R_PPC64_REL24      net_set_todo
  150:   00 00 82 3c     addis   r4,r2,0

GCC didn't insert a nop after the branch to net_set_todo() because it's
a sibling call, so it never returns.  The nop isn't needed after the
branch in that case.

Signed-off-by: Josh Poimboeuf 
Acked-by: Naveen N. Rao 
Reviewed-and-tested-by: Kamalesh Babulal 
Signed-off-by: Michael Ellerman

powerpc: Fix boot on BOOK3S_32 with CONFIG_STRICT_KERNEL_RWX

2017-11-22T12:04:20+00:00

On powerpc32, patch_instruction() is called by apply_feature_fixups()
which is called from early_init()

There is the following note in front of early_init():
 * Note that the kernel may be running at an address which is different
 * from the address that it was linked at, so we must use RELOC/PTRRELOC
 * to access static data (including strings).  -- paulus

Therefore, slab_is_available() cannot be called yet, and
text_poke_area must be addressed with PTRRELOC()

Fixes: 95902e6c8864 ("powerpc/mm: Implement STRICT_KERNEL_RWX on PPC32")
Cc: stable@vger.kernel.org # v4.14+
Reported-by: Meelis Roos 
Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman

powerpc/lib/code-patching: Use alternate map for patch_instruction()

2017-07-03T13:12:19+00:00

This patch creates the window using text_poke_area, allocated via
get_vm_area(). text_poke_area is per CPU to avoid locking.
text_poke_area for each cpu is setup using late_initcall, prior to
setup of these alternate mapping areas, we continue to use direct
write to change/modify kernel text. With the ability to use alternate
mappings to write to kernel text, it provides us the freedom to then
turn text read-only and implement CONFIG_STRICT_KERNEL_RWX.

This code is CPU hotplug aware to ensure that the we have mappings for
any new cpus as they come online and tear down mappings for any CPUs
that go offline.

Signed-off-by: Balbir Singh 
Signed-off-by: Michael Ellerman

powerpc/kprobes: Convert __kprobes to NOKPROBE_SYMBOL()

2017-04-23T10:32:25+00:00

Along similar lines as commit 9326638cbee2 ("kprobes, x86: Use NOKPROBE_SYMBOL()
instead of __kprobes annotation"), convert __kprobes annotation to either
NOKPROBE_SYMBOL() or nokprobe_inline. The latter forces inlining, in which case
the caller needs to be added to NOKPROBE_SYMBOL().

Also:
 - blacklist arch_deref_entry_point(), and
 - convert a few regular inlines to nokprobe_inline in lib/sstep.c

A key benefit is the ability to detect such symbols as being
blacklisted. Before this patch:

  $ cat /sys/kernel/debug/kprobes/blacklist | grep read_mem
  $ perf probe read_mem
  Failed to write event: Invalid argument
    Error: Failed to add events.
  $ dmesg | tail -1
  [ 3736.112815] Could not insert probe at _text+10014968: -22

After patch:
  $ cat /sys/kernel/debug/kprobes/blacklist | grep read_mem
  0xc000000000072b50-0xc000000000072d20	read_mem
  $ perf probe read_mem
  read_mem is blacklisted function, skip it.
  Added new events:
    (null):(null)        (on read_mem)
    probe:read_mem       (on read_mem)

  You can now use it in all perf tools, such as:

	  perf record -e probe:read_mem -aR sleep 1

  $ grep " read_mem" /proc/kallsyms
  c000000000072b50 t read_mem
  c0000000005f3b40 t read_mem
  $ cat /sys/kernel/debug/kprobes/list
  c0000000005f3b48  k  read_mem+0x8    [DISABLED]

Acked-by: Masami Hiramatsu 
Signed-off-by: Naveen N. Rao 
[mpe: Minor change log formatting, fix up some conflicts]
Signed-off-by: Michael Ellerman

kprobes: move kprobe declarations to asm-generic/kprobes.h

2017-02-28T02:43:45+00:00

Often all is needed is these small helpers, instead of compiler.h or a
full kprobes.h.  This is important for asm helpers, in fact even some
asm/kprobes.h make use of these helpers...  instead just keep a generic
asm file with helpers useful for asm code with the least amount of
clutter as possible.

Likewise we need now to also address what to do about this file for both
when architectures have CONFIG_HAVE_KPROBES, and when they do not.  Then
for when architectures have CONFIG_HAVE_KPROBES but have disabled
CONFIG_KPROBES.

Right now most asm/kprobes.h do not have guards against CONFIG_KPROBES,
this means most architecture code cannot include asm/kprobes.h safely.
Correct this and add guards for architectures missing them.
Additionally provide architectures that not have kprobes support with
the default asm-generic solution.  This lets us force asm/kprobes.h on
the header include/linux/kprobes.h always, but most importantly we can
now safely include just asm/kprobes.h on architecture code without
bringing the full kitchen sink of header files.

Two architectures already provided a guard against CONFIG_KPROBES on its
kprobes.h: sh, arch.  The rest of the architectures needed gaurds added.
We avoid including any not-needed headers on asm/kprobes.h unless
kprobes have been enabled.

In a subsequent atomic change we can try now to remove compiler.h from
include/linux/kprobes.h.

During this sweep I've also identified a few architectures defining a
common macro needed for both kprobes and ftrace, that of the definition
of the breakput instruction up.  Some refer to this as
BREAKPOINT_INSTRUCTION.  This must be kept outside of the #ifdef
CONFIG_KPROBES guard.

[mcgrof@kernel.org: fix arm64 build]
  Link: http://lkml.kernel.org/r/CAB=NE6X1WMByuARS4mZ1g9+W=LuVBnMDnh_5zyN0CLADaVh=Jw@mail.gmail.com
[sfr@canb.auug.org.au: fixup for kprobes declarations moving]
  Link: http://lkml.kernel.org/r/20170214165933.13ebd4f4@canb.auug.org.au
Link: http://lkml.kernel.org/r/20170203233139.32682-1-mcgrof@kernel.org
Signed-off-by: Luis R. Rodriguez 
Signed-off-by: Stephen Rothwell 
Acked-by: Masami Hiramatsu 
Cc: Arnd Bergmann 
Cc: Masami Hiramatsu 
Cc: Ananth N Mavinakayanahalli 
Cc: Anil S Keshavamurthy 
Cc: David S. Miller 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: H. Peter Anvin 
Cc: Andy Lutomirski 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds