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docs: livepatch: convert docs to ReST and rename to *.rst 

Convert livepatch documentation to ReST format. The changes
are mostly trivial, as the documents are already on a good
shape. Just a few markup changes are needed for Sphinx to
properly parse the docs.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - The in-file TOC becomes a comment, in order to skip it from the
    output, as Sphinx already generates an index there.
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab 2019-05-03 16:30:23 +02:00 committed by Jonathan Corbet
parent 894ee5ff83
commit 89e33ea732
8 changed files with 224 additions and 163 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Documentation/ABI/testing/sysfs-kernel-livepatch
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@ -45,7 +45,7 @@ Description:
use this feature without a clearance from a patch use this feature without a clearance from a patch
distributor. Removal (rmmod) of patch modules is permanently distributor. Removal (rmmod) of patch modules is permanently
disabled when the feature is used. See disabled when the feature is used. See
Documentation/livepatch/livepatch.txt for more information. Documentation/livepatch/livepatch.rst for more information.
What: /sys/kernel/livepatch/<patch>/<object> What: /sys/kernel/livepatch/<patch>/<object>
Date: Nov 2014 Date: Nov 2014

12
Documentation/livepatch/callbacks.txt → Documentation/livepatch/callbacks.rst
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@ -30,16 +30,20 @@ be patched, irrespective of the target klp_object's current state.
Callbacks can be registered for the following livepatch actions: Callbacks can be registered for the following livepatch actions:
* Pre-patch - before a klp_object is patched * Pre-patch
- before a klp_object is patched
* Post-patch - after a klp_object has been patched and is active * Post-patch
- after a klp_object has been patched and is active
across all tasks across all tasks
* Pre-unpatch - before a klp_object is unpatched (ie, patched code is * Pre-unpatch
- before a klp_object is unpatched (ie, patched code is
active), used to clean up post-patch callback active), used to clean up post-patch callback
resources resources
* Post-unpatch - after a klp_object has been patched, all code has * Post-unpatch
- after a klp_object has been patched, all code has
been restored and no tasks are running patched code, been restored and no tasks are running patched code,
used to cleanup pre-patch callback resources used to cleanup pre-patch callback resources

14
Documentation/livepatch/cumulative-patches.txt → Documentation/livepatch/cumulative-patches.rst
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@ -18,7 +18,7 @@ Usage
----- -----
The atomic replace can be enabled by setting "replace" flag in struct klp_patch, The atomic replace can be enabled by setting "replace" flag in struct klp_patch,
for example: for example::
static struct klp_patch patch = { static struct klp_patch patch = {
.mod = THIS_MODULE, .mod = THIS_MODULE,
@ -49,19 +49,19 @@ Features
The atomic replace allows: The atomic replace allows:
+ Atomically revert some functions in a previous patch while - Atomically revert some functions in a previous patch while
upgrading other functions. upgrading other functions.
+ Remove eventual performance impact caused by core redirection - Remove eventual performance impact caused by core redirection
for functions that are no longer patched. for functions that are no longer patched.
+ Decrease user confusion about dependencies between livepatches. - Decrease user confusion about dependencies between livepatches.
Limitations: Limitations:
------------ ------------
+ Once the operation finishes, there is no straightforward way - Once the operation finishes, there is no straightforward way
to reverse it and restore the replaced patches atomically. to reverse it and restore the replaced patches atomically.
A good practice is to set .replace flag in any released livepatch. A good practice is to set .replace flag in any released livepatch.
@ -74,7 +74,7 @@ Limitations:
only when the transition was not forced. only when the transition was not forced.
+ Only the (un)patching callbacks from the _new_ cumulative livepatch are - Only the (un)patching callbacks from the _new_ cumulative livepatch are
executed. Any callbacks from the replaced patches are ignored. executed. Any callbacks from the replaced patches are ignored.
In other words, the cumulative patch is responsible for doing any actions In other words, the cumulative patch is responsible for doing any actions
@ -93,7 +93,7 @@ Limitations:
enabled patches were called. enabled patches were called.
+ There is no special handling of shadow variables. Livepatch authors - There is no special handling of shadow variables. Livepatch authors
must create their own rules how to pass them from one cumulative must create their own rules how to pass them from one cumulative
patch to the other. Especially that they should not blindly remove patch to the other. Especially that they should not blindly remove
them in module_exit() functions. them in module_exit() functions.

21
Documentation/livepatch/index.rst Normal file
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@ -0,0 +1,21 @@
:orphan:
===================
Kernel Livepatching
===================
.. toctree::
:maxdepth: 1
livepatch
callbacks
cumulative-patches
module-elf-format
shadow-vars
.. only:: subproject and html
Indices
=======
* :ref:`genindex`

60
Documentation/livepatch/livepatch.txt → Documentation/livepatch/livepatch.rst
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@ -4,22 +4,22 @@ Livepatch
This document outlines basic information about kernel livepatching. This document outlines basic information about kernel livepatching.
Table of Contents: .. Table of Contents:
1. Motivation 1. Motivation
2. Kprobes, Ftrace, Livepatching 2. Kprobes, Ftrace, Livepatching
3. Consistency model 3. Consistency model
4. Livepatch module 4. Livepatch module
4.1. New functions 4.1. New functions
4.2. Metadata 4.2. Metadata
5. Livepatch life-cycle 5. Livepatch life-cycle
5.1. Loading 5.1. Loading
5.2. Enabling 5.2. Enabling
5.3. Replacing 5.3. Replacing
5.4. Disabling 5.4. Disabling
5.5. Removing 5.5. Removing
6. Sysfs 6. Sysfs
7. Limitations 7. Limitations
1. Motivation 1. Motivation
@ -40,14 +40,14 @@ There are multiple mechanisms in the Linux kernel that are directly related
to redirection of code execution; namely: kernel probes, function tracing, to redirection of code execution; namely: kernel probes, function tracing,
and livepatching: and livepatching:
+ The kernel probes are the most generic. The code can be redirected by - The kernel probes are the most generic. The code can be redirected by
putting a breakpoint instruction instead of any instruction. putting a breakpoint instruction instead of any instruction.
+ The function tracer calls the code from a predefined location that is - The function tracer calls the code from a predefined location that is
close to the function entry point. This location is generated by the close to the function entry point. This location is generated by the
compiler using the '-pg' gcc option. compiler using the '-pg' gcc option.
+ Livepatching typically needs to redirect the code at the very beginning - Livepatching typically needs to redirect the code at the very beginning
of the function entry before the function parameters or the stack of the function entry before the function parameters or the stack
are in any way modified. are in any way modified.
@ -249,7 +249,7 @@ The patch contains only functions that are really modified. But they
might want to access functions or data from the original source file might want to access functions or data from the original source file
that may only be locally accessible. This can be solved by a special that may only be locally accessible. This can be solved by a special
relocation section in the generated livepatch module, see relocation section in the generated livepatch module, see
Documentation/livepatch/module-elf-format.txt for more details. Documentation/livepatch/module-elf-format.rst for more details.
4.2. Metadata 4.2. Metadata
@ -258,7 +258,7 @@ Documentation/livepatch/module-elf-format.txt for more details.
The patch is described by several structures that split the information The patch is described by several structures that split the information
into three levels: into three levels:
+ struct klp_func is defined for each patched function. It describes - struct klp_func is defined for each patched function. It describes
the relation between the original and the new implementation of a the relation between the original and the new implementation of a
particular function. particular function.
@ -275,7 +275,7 @@ into three levels:
only for a particular object ( vmlinux or a kernel module ). Note that only for a particular object ( vmlinux or a kernel module ). Note that
kallsyms allows for searching symbols according to the object name. kallsyms allows for searching symbols according to the object name.
+ struct klp_object defines an array of patched functions (struct - struct klp_object defines an array of patched functions (struct
klp_func) in the same object. Where the object is either vmlinux klp_func) in the same object. Where the object is either vmlinux
(NULL) or a module name. (NULL) or a module name.
@ -285,7 +285,7 @@ into three levels:
only when they are available. only when they are available.
+ struct klp_patch defines an array of patched objects (struct - struct klp_patch defines an array of patched objects (struct
klp_object). klp_object).
This structure handles all patched functions consistently and eventually, This structure handles all patched functions consistently and eventually,
@ -337,14 +337,16 @@ operation fails.
Second, livepatch enters into a transition state where tasks are converging Second, livepatch enters into a transition state where tasks are converging
to the patched state. If an original function is patched for the first to the patched state. If an original function is patched for the first
time, a function specific struct klp_ops is created and an universal time, a function specific struct klp_ops is created and an universal
ftrace handler is registered[*]. This stage is indicated by a value of '1' ftrace handler is registered\ [#]_. This stage is indicated by a value of '1'
in /sys/kernel/livepatch/<name>/transition. For more information about in /sys/kernel/livepatch/<name>/transition. For more information about
this process, see the "Consistency model" section. this process, see the "Consistency model" section.
Finally, once all tasks have been patched, the 'transition' value changes Finally, once all tasks have been patched, the 'transition' value changes
to '0'. to '0'.
[*] Note that functions might be patched multiple times. The ftrace handler .. [#]
Note that functions might be patched multiple times. The ftrace handler
is registered only once for a given function. Further patches just add is registered only once for a given function. Further patches just add
an entry to the list (see field `func_stack`) of the struct klp_ops. an entry to the list (see field `func_stack`) of the struct klp_ops.
The right implementation is selected by the ftrace handler, see The right implementation is selected by the ftrace handler, see
@ -368,7 +370,7 @@ the ftrace handler is unregistered and the struct klp_ops is
freed when the related function is not modified by the new patch freed when the related function is not modified by the new patch
and func_stack list becomes empty. and func_stack list becomes empty.
See Documentation/livepatch/cumulative-patches.txt for more details. See Documentation/livepatch/cumulative-patches.rst for more details.
5.4. Disabling 5.4. Disabling
@ -421,7 +423,7 @@ See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
The current Livepatch implementation has several limitations: The current Livepatch implementation has several limitations:
+ Only functions that can be traced could be patched. - Only functions that can be traced could be patched.
Livepatch is based on the dynamic ftrace. In particular, functions Livepatch is based on the dynamic ftrace. In particular, functions
implementing ftrace or the livepatch ftrace handler could not be implementing ftrace or the livepatch ftrace handler could not be
@ -431,7 +433,7 @@ The current Livepatch implementation has several limitations:
+ Livepatch works reliably only when the dynamic ftrace is located at - Livepatch works reliably only when the dynamic ftrace is located at
the very beginning of the function. the very beginning of the function.
The function need to be redirected before the stack or the function The function need to be redirected before the stack or the function
@ -445,7 +447,7 @@ The current Livepatch implementation has several limitations:
this is handled on the ftrace level. this is handled on the ftrace level.
+ Kretprobes using the ftrace framework conflict with the patched - Kretprobes using the ftrace framework conflict with the patched
functions. functions.
Both kretprobes and livepatches use a ftrace handler that modifies Both kretprobes and livepatches use a ftrace handler that modifies
@ -453,7 +455,7 @@ The current Livepatch implementation has several limitations:
is rejected when the handler is already in use by the other. is rejected when the handler is already in use by the other.
+ Kprobes in the original function are ignored when the code is - Kprobes in the original function are ignored when the code is
redirected to the new implementation. redirected to the new implementation.
There is a work in progress to add warnings about this situation. There is a work in progress to add warnings about this situation.

211
Documentation/livepatch/module-elf-format.txt → Documentation/livepatch/module-elf-format.rst
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@ -4,29 +4,29 @@ Livepatch module Elf format
This document outlines the Elf format requirements that livepatch modules must follow. This document outlines the Elf format requirements that livepatch modules must follow.
-----------------
Table of Contents .. Table of Contents
-----------------
0. Background and motivation 0. Background and motivation
1. Livepatch modinfo field 1. Livepatch modinfo field
2. Livepatch relocation sections 2. Livepatch relocation sections
2.1 What are livepatch relocation sections? 2.1 What are livepatch relocation sections?
2.2 Livepatch relocation section format 2.2 Livepatch relocation section format
2.2.1 Required flags 2.2.1 Required flags
2.2.2 Required name format 2.2.2 Required name format
2.2.3 Example livepatch relocation section names 2.2.3 Example livepatch relocation section names
2.2.4 Example `readelf --sections` output 2.2.4 Example `readelf --sections` output
2.2.5 Example `readelf --relocs` output 2.2.5 Example `readelf --relocs` output
3. Livepatch symbols 3. Livepatch symbols
3.1 What are livepatch symbols? 3.1 What are livepatch symbols?
3.2 A livepatch module's symbol table 3.2 A livepatch module's symbol table
3.3 Livepatch symbol format 3.3 Livepatch symbol format
3.3.1 Required flags 3.3.1 Required flags
3.3.2 Required name format 3.3.2 Required name format
3.3.3 Example livepatch symbol names 3.3.3 Example livepatch symbol names
3.3.4 Example `readelf --symbols` output 3.3.4 Example `readelf --symbols` output
4. Architecture-specific sections 4. Architecture-specific sections
5. Symbol table and Elf section access 5. Symbol table and Elf section access
---------------------------- ----------------------------
0. Background and motivation 0. Background and motivation
@ -89,12 +89,15 @@ used by the kernel module loader to identify livepatch modules.
Example modinfo output: Example modinfo output:
----------------------- -----------------------
% modinfo livepatch-meminfo.ko
filename: livepatch-meminfo.ko ::
livepatch: Y
license: GPL % modinfo livepatch-meminfo.ko
depends: filename: livepatch-meminfo.ko
vermagic: 4.3.0+ SMP mod_unload livepatch: Y
license: GPL
depends:
vermagic: 4.3.0+ SMP mod_unload
-------------------------------- --------------------------------
2. Livepatch relocation sections 2. Livepatch relocation sections
@ -142,17 +145,18 @@ be copied into memory along with the other SHF_ALLOC sections).
2.2.2 Required name format 2.2.2 Required name format
-------------------------- --------------------------
The name of a livepatch relocation section must conform to the following format: The name of a livepatch relocation section must conform to the following
format::
.klp.rela.objname.section_name .klp.rela.objname.section_name
^ ^^ ^ ^ ^ ^ ^^ ^ ^ ^
|________||_____| |__________| |________||_____| |__________|
[A] [B] [C] [A] [B] [C]
[A] The relocation section name is prefixed with the string ".klp.rela." [A] The relocation section name is prefixed with the string ".klp.rela."
[B] The name of the object (i.e. "vmlinux" or name of module) to [B] The name of the object (i.e. "vmlinux" or name of module) to
which the relocation section belongs follows immediately after the prefix. which the relocation section belongs follows immediately after the prefix.
[C] The actual name of the section to which this relocation section applies. [C] The actual name of the section to which this relocation section applies.
2.2.3 Example livepatch relocation section names: 2.2.3 Example livepatch relocation section names:
------------------------------------------------- -------------------------------------------------
@ -162,6 +166,9 @@ The name of a livepatch relocation section must conform to the following format:
2.2.4 Example `readelf --sections` output for a patch 2.2.4 Example `readelf --sections` output for a patch
module that patches vmlinux and modules 9p, btrfs, ext4: module that patches vmlinux and modules 9p, btrfs, ext4:
-------------------------------------------------------- --------------------------------------------------------
::
Section Headers: Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al [Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ snip ] [ snip ]
@ -175,23 +182,26 @@ module that patches vmlinux and modules 9p, btrfs, ext4:
[ snip ] ^ ^ [ snip ] ^ ^
| | | |
[*] [*] [*] [*]
[*] Livepatch relocation sections are SHT_RELA sections but with a few special [*] Livepatch relocation sections are SHT_RELA sections but with a few special
characteristics. Notice that they are marked SHF_ALLOC ("A") so that they will characteristics. Notice that they are marked SHF_ALLOC ("A") so that they will
not be discarded when the module is loaded into memory, as well as with the not be discarded when the module is loaded into memory, as well as with the
SHF_RELA_LIVEPATCH flag ("o" - for OS-specific). SHF_RELA_LIVEPATCH flag ("o" - for OS-specific).
2.2.5 Example `readelf --relocs` output for a patch module: 2.2.5 Example `readelf --relocs` output for a patch module:
----------------------------------------------------------- -----------------------------------------------------------
Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend ::
000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
0000000000000028 0000003d0000000b R_X86_64_32S 0000000000000000 .klp.sym.btrfs.btrfs_ktype,0 + 0 Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
0000000000000036 0000003b00000002 R_X86_64_PC32 0000000000000000 .klp.sym.btrfs.can_modify_feature.isra.3,0 - 4 Offset Info Type Symbol's Value Symbol's Name + Addend
000000000000004c 0000004900000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.snprintf,0 - 4 000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
[ snip ] ^ 0000000000000028 0000003d0000000b R_X86_64_32S 0000000000000000 .klp.sym.btrfs.btrfs_ktype,0 + 0
| 0000000000000036 0000003b00000002 R_X86_64_PC32 0000000000000000 .klp.sym.btrfs.can_modify_feature.isra.3,0 - 4
000000000000004c 0000004900000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.snprintf,0 - 4
[ snip ] ^
|
[*] [*]
[*] Every symbol referenced by a relocation is a livepatch symbol. [*] Every symbol referenced by a relocation is a livepatch symbol.
-------------------- --------------------
3. Livepatch symbols 3. Livepatch symbols
@ -231,18 +241,19 @@ relocation section refer to their respective symbols with their symbol indices,
and the original symbol indices (and thus the symtab ordering) must be and the original symbol indices (and thus the symtab ordering) must be
preserved in order for apply_relocate_add() to find the right symbol. preserved in order for apply_relocate_add() to find the right symbol.
For example, take this particular rela from a livepatch module: For example, take this particular rela from a livepatch module:::
Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
This rela refers to the symbol '.klp.sym.vmlinux.printk,0', and the symbol index is encoded Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the Offset Info Type Symbol's Value Symbol's Name + Addend
symbol index 94. 000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
And in this patch module's corresponding symbol table, symbol index 94 refers to that very symbol:
[ snip ] This rela refers to the symbol '.klp.sym.vmlinux.printk,0', and the symbol index is encoded
94: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.printk,0 in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the
[ snip ] symbol index 94.
And in this patch module's corresponding symbol table, symbol index 94 refers to that very symbol:
[ snip ]
94: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.printk,0
[ snip ]
--------------------------- ---------------------------
3.3 Livepatch symbol format 3.3 Livepatch symbol format
@ -256,42 +267,48 @@ See include/uapi/linux/elf.h for the actual definitions.
3.3.2 Required name format 3.3.2 Required name format
-------------------------- --------------------------
Livepatch symbol names must conform to the following format: Livepatch symbol names must conform to the following format::
.klp.sym.objname.symbol_name,sympos .klp.sym.objname.symbol_name,sympos
^ ^^ ^ ^ ^ ^ ^ ^^ ^ ^ ^ ^
|_______||_____| |_________| | |_______||_____| |_________| |
[A] [B] [C] [D] [A] [B] [C] [D]
[A] The symbol name is prefixed with the string ".klp.sym." [A] The symbol name is prefixed with the string ".klp.sym."
[B] The name of the object (i.e. "vmlinux" or name of module) to [B] The name of the object (i.e. "vmlinux" or name of module) to
which the symbol belongs follows immediately after the prefix. which the symbol belongs follows immediately after the prefix.
[C] The actual name of the symbol. [C] The actual name of the symbol.
[D] The position of the symbol in the object (as according to kallsyms) [D] The position of the symbol in the object (as according to kallsyms)
This is used to differentiate duplicate symbols within the same This is used to differentiate duplicate symbols within the same
object. The symbol position is expressed numerically (0, 1, 2...). object. The symbol position is expressed numerically (0, 1, 2...).
The symbol position of a unique symbol is 0. The symbol position of a unique symbol is 0.
3.3.3 Example livepatch symbol names: 3.3.3 Example livepatch symbol names:
------------------------------------- -------------------------------------
.klp.sym.vmlinux.snprintf,0
.klp.sym.vmlinux.printk,0 ::
.klp.sym.btrfs.btrfs_ktype,0
.klp.sym.vmlinux.snprintf,0
.klp.sym.vmlinux.printk,0
.klp.sym.btrfs.btrfs_ktype,0
3.3.4 Example `readelf --symbols` output for a patch module: 3.3.4 Example `readelf --symbols` output for a patch module:
------------------------------------------------------------ ------------------------------------------------------------
Symbol table '.symtab' contains 127 entries:
Num: Value Size Type Bind Vis Ndx Name ::
[ snip ]
73: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.snprintf,0 Symbol table '.symtab' contains 127 entries:
74: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.capable,0 Num: Value Size Type Bind Vis Ndx Name
75: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.find_next_bit,0 [ snip ]
76: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.si_swapinfo,0 73: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.snprintf,0
[ snip ] ^ 74: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.capable,0
| 75: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.find_next_bit,0
[*] 76: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.si_swapinfo,0
[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20). [ snip ] ^
"OS" means OS-specific. |
[*]
[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
"OS" means OS-specific.
--------------------------------- ---------------------------------
4. Architecture-specific sections 4. Architecture-specific sections
@ -313,11 +330,11 @@ Since apply_relocate_add() requires access to a module's section headers,
symbol table, and relocation section indices, Elf information is preserved for symbol table, and relocation section indices, Elf information is preserved for
livepatch modules and is made accessible by the module loader through livepatch modules and is made accessible by the module loader through
module->klp_info, which is a klp_modinfo struct. When a livepatch module loads, module->klp_info, which is a klp_modinfo struct. When a livepatch module loads,
this struct is filled in by the module loader. Its fields are documented below: this struct is filled in by the module loader. Its fields are documented below::
struct klp_modinfo { struct klp_modinfo {
Elf_Ehdr hdr; /* Elf header */ Elf_Ehdr hdr; /* Elf header */
Elf_Shdr *sechdrs; /* Section header table */ Elf_Shdr *sechdrs; /* Section header table */
char *secstrings; /* String table for the section headers */ char *secstrings; /* String table for the section headers */
unsigned int symndx; /* The symbol table section index */ unsigned int symndx; /* The symbol table section index */
}; };

65
Documentation/livepatch/shadow-vars.txt → Documentation/livepatch/shadow-vars.rst
View File

@ -27,10 +27,13 @@ A hashtable references all shadow variables. These references are
stored and retrieved through a <obj, id> pair. stored and retrieved through a <obj, id> pair.
* The klp_shadow variable data structure encapsulates both tracking * The klp_shadow variable data structure encapsulates both tracking
meta-data and shadow-data: meta-data and shadow-data:
- meta-data - meta-data
- obj - pointer to parent object - obj - pointer to parent object
- id - data identifier - id - data identifier
- data[] - storage for shadow data - data[] - storage for shadow data
It is important to note that the klp_shadow_alloc() and It is important to note that the klp_shadow_alloc() and
@ -47,31 +50,43 @@ to do actions that can be done only once when a new variable is allocated.
* klp_shadow_alloc() - allocate and add a new shadow variable * klp_shadow_alloc() - allocate and add a new shadow variable
- search hashtable for <obj, id> pair - search hashtable for <obj, id> pair
- if exists - if exists
- WARN and return NULL - WARN and return NULL
- if <obj, id> doesn't already exist - if <obj, id> doesn't already exist
- allocate a new shadow variable - allocate a new shadow variable
- initialize the variable using a custom constructor and data when provided - initialize the variable using a custom constructor and data when provided
- add <obj, id> to the global hashtable - add <obj, id> to the global hashtable
* klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable * klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable
- search hashtable for <obj, id> pair - search hashtable for <obj, id> pair
- if exists - if exists
- return existing shadow variable - return existing shadow variable
- if <obj, id> doesn't already exist - if <obj, id> doesn't already exist
- allocate a new shadow variable - allocate a new shadow variable
- initialize the variable using a custom constructor and data when provided - initialize the variable using a custom constructor and data when provided
- add <obj, id> pair to the global hashtable - add <obj, id> pair to the global hashtable
* klp_shadow_free() - detach and free a <obj, id> shadow variable * klp_shadow_free() - detach and free a <obj, id> shadow variable
- find and remove a <obj, id> reference from global hashtable - find and remove a <obj, id> reference from global hashtable
- if found - if found
- call destructor function if defined - call destructor function if defined
- free shadow variable - free shadow variable
* klp_shadow_free_all() - detach and free all <*, id> shadow variables * klp_shadow_free_all() - detach and free all <*, id> shadow variables
- find and remove any <*, id> references from global hashtable - find and remove any <*, id> references from global hashtable
- if found - if found
- call destructor function if defined - call destructor function if defined
- free shadow variable - free shadow variable
@ -102,12 +117,12 @@ parent "goes live" (ie, any shadow variable get-API requests are made
for this <obj, id> pair.) for this <obj, id> pair.)
For commit 1d147bfa6429, when a parent sta_info structure is allocated, For commit 1d147bfa6429, when a parent sta_info structure is allocated,
allocate a shadow copy of the ps_lock pointer, then initialize it: allocate a shadow copy of the ps_lock pointer, then initialize it::
#define PS_LOCK 1 #define PS_LOCK 1
struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata, struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
const u8 *addr, gfp_t gfp) const u8 *addr, gfp_t gfp)
{ {
struct sta_info *sta; struct sta_info *sta;
spinlock_t *ps_lock; spinlock_t *ps_lock;
@ -123,10 +138,10 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
... ...
When requiring a ps_lock, query the shadow variable API to retrieve one When requiring a ps_lock, query the shadow variable API to retrieve one
for a specific struct sta_info: for a specific struct sta_info:::
void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta) void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
{ {
spinlock_t *ps_lock; spinlock_t *ps_lock;
/* sync with ieee80211_tx_h_unicast_ps_buf */ /* sync with ieee80211_tx_h_unicast_ps_buf */
@ -136,10 +151,10 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
... ...
When the parent sta_info structure is freed, first free the shadow When the parent sta_info structure is freed, first free the shadow
variable: variable::
void sta_info_free(struct ieee80211_local *local, struct sta_info *sta) void sta_info_free(struct ieee80211_local *local, struct sta_info *sta)
{ {
klp_shadow_free(sta, PS_LOCK, NULL); klp_shadow_free(sta, PS_LOCK, NULL);
kfree(sta); kfree(sta);
... ...
@ -155,19 +170,19 @@ these cases, the klp_shadow_get_or_alloc() call can be used to attach
shadow variables to parents already in-flight. shadow variables to parents already in-flight.
For commit 1d147bfa6429, a good spot to allocate a shadow spinlock is For commit 1d147bfa6429, a good spot to allocate a shadow spinlock is
inside ieee80211_sta_ps_deliver_wakeup(): inside ieee80211_sta_ps_deliver_wakeup()::
int ps_lock_shadow_ctor(void *obj, void *shadow_data, void *ctor_data) int ps_lock_shadow_ctor(void *obj, void *shadow_data, void *ctor_data)
{ {
spinlock_t *lock = shadow_data; spinlock_t *lock = shadow_data;
spin_lock_init(lock); spin_lock_init(lock);
return 0; return 0;
} }
#define PS_LOCK 1 #define PS_LOCK 1
void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta) void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
{ {
spinlock_t *ps_lock; spinlock_t *ps_lock;
/* sync with ieee80211_tx_h_unicast_ps_buf */ /* sync with ieee80211_tx_h_unicast_ps_buf */
@ -200,10 +215,12 @@ suggests how to handle the parent object.
============= =============
* https://github.com/dynup/kpatch * https://github.com/dynup/kpatch
The livepatch implementation is based on the kpatch version of shadow
variables. The livepatch implementation is based on the kpatch version of shadow
variables.
* http://files.mkgnu.net/files/dynamos/doc/papers/dynamos_eurosys_07.pdf * http://files.mkgnu.net/files/dynamos/doc/papers/dynamos_eurosys_07.pdf
Dynamic and Adaptive Updates of Non-Quiescent Subsystems in Commodity
Operating System Kernels (Kritis Makris, Kyung Dong Ryu 2007) presented Dynamic and Adaptive Updates of Non-Quiescent Subsystems in Commodity
a datatype update technique called "shadow data structures". Operating System Kernels (Kritis Makris, Kyung Dong Ryu 2007) presented
a datatype update technique called "shadow data structures".

2
tools/objtool/Documentation/stack-validation.txt
View File

@ -111,7 +111,7 @@ c) Higher live patching compatibility rate
be detectable). Objtool makes that possible. be detectable). Objtool makes that possible.
For more details, see the livepatch documentation in the Linux kernel For more details, see the livepatch documentation in the Linux kernel
source tree at Documentation/livepatch/livepatch.txt. source tree at Documentation/livepatch/livepatch.rst.
Rules Rules
----- -----