diff options
Diffstat (limited to 'Documentation/livepatch')
| -rw-r--r-- | Documentation/livepatch/callbacks.rst (renamed from Documentation/livepatch/callbacks.txt) | 45 | ||||
| -rw-r--r-- | Documentation/livepatch/cumulative-patches.rst (renamed from Documentation/livepatch/cumulative-patches.txt) | 14 | ||||
| -rw-r--r-- | Documentation/livepatch/index.rst | 21 | ||||
| -rw-r--r-- | Documentation/livepatch/livepatch.rst (renamed from Documentation/livepatch/livepatch.txt) | 62 | ||||
| -rw-r--r-- | Documentation/livepatch/module-elf-format.rst (renamed from Documentation/livepatch/module-elf-format.txt) | 353 | ||||
| -rw-r--r-- | Documentation/livepatch/shadow-vars.rst (renamed from Documentation/livepatch/shadow-vars.txt) | 65 |
6 files changed, 305 insertions, 255 deletions
diff --git a/Documentation/livepatch/callbacks.txt b/Documentation/livepatch/callbacks.rst index 182e31d4abce..470944aa8658 100644 --- a/Documentation/livepatch/callbacks.txt +++ b/Documentation/livepatch/callbacks.rst @@ -4,7 +4,7 @@ Livepatch (un)patch-callbacks provide a mechanism for livepatch modules to execute callback functions when a kernel object is (un)patched. They -can be considered a "power feature" that extends livepatching abilities +can be considered a **power feature** that **extends livepatching abilities** to include: - Safe updates to global data @@ -17,6 +17,9 @@ In most cases, (un)patch callbacks will need to be used in conjunction with memory barriers and kernel synchronization primitives, like mutexes/spinlocks, or even stop_machine(), to avoid concurrency issues. +1. Motivation +============= + Callbacks differ from existing kernel facilities: - Module init/exit code doesn't run when disabling and re-enabling a @@ -28,21 +31,31 @@ Callbacks are part of the klp_object structure and their implementation is specific to that klp_object. Other livepatch objects may or may not be patched, irrespective of the target klp_object's current state. +2. Callback types +================= + 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 - * 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 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, used to cleanup pre-patch callback resources +3. How it works +=============== + Each callback is optional, omitting one does not preclude specifying any other. However, the livepatching core executes the handlers in symmetry: pre-patch callbacks have a post-unpatch counterpart and @@ -86,11 +99,14 @@ If the object did successfully patch, but the patch transition never started for some reason (e.g., if another object failed to patch), only the post-unpatch callback will be called. +4. Use cases +============ -Example Use-cases -================= +Sample livepatch modules demonstrating the callback API can be found in +samples/livepatch/ directory. These samples were modified for use in +kselftests and can be found in the lib/livepatch directory. -Update global data +Global data update ------------------ A pre-patch callback can be useful to update a global variable. For @@ -103,24 +119,15 @@ patch the data *after* patching is complete with a post-patch callback, so that tcp_send_challenge_ack() could first be changed to read sysctl_tcp_challenge_ack_limit with READ_ONCE. - -Support __init and probe function patches +__init and probe function patches support ----------------------------------------- Although __init and probe functions are not directly livepatch-able, it may be possible to implement similar updates via pre/post-patch callbacks. -48900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST") change the way that +The commit ``48900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST")`` change the way that virtnet_probe() initialized its driver's net_device features. A pre/post-patch callback could iterate over all such devices, making a similar change to their hw_features value. (Client functions of the value may need to be updated accordingly.) - - -Other Examples -============== - -Sample livepatch modules demonstrating the callback API can be found in -samples/livepatch/ directory. These samples were modified for use in -kselftests and can be found in the lib/livepatch directory. diff --git a/Documentation/livepatch/cumulative-patches.txt b/Documentation/livepatch/cumulative-patches.rst index 0012808e8d44..1931f318976a 100644 --- a/Documentation/livepatch/cumulative-patches.txt +++ b/Documentation/livepatch/cumulative-patches.rst @@ -18,7 +18,7 @@ Usage ----- The atomic replace can be enabled by setting "replace" flag in struct klp_patch, -for example: +for example:: static struct klp_patch patch = { .mod = THIS_MODULE, @@ -49,19 +49,19 @@ Features 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. - + Remove eventual performance impact caused by core redirection + - Remove eventual performance impact caused by core redirection for functions that are no longer patched. - + Decrease user confusion about dependencies between livepatches. + - Decrease user confusion about dependencies between livepatches. 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. 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 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. In other words, the cumulative patch is responsible for doing any actions @@ -93,7 +93,7 @@ Limitations: 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 patch to the other. Especially that they should not blindly remove them in module_exit() functions. diff --git a/Documentation/livepatch/index.rst b/Documentation/livepatch/index.rst new file mode 100644 index 000000000000..edd291d51847 --- /dev/null +++ b/Documentation/livepatch/index.rst @@ -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` diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.rst index 4627b41ff02e..c2c598c4ead8 100644 --- a/Documentation/livepatch/livepatch.txt +++ b/Documentation/livepatch/livepatch.rst @@ -4,22 +4,22 @@ Livepatch This document outlines basic information about kernel livepatching. -Table of Contents: - -1. Motivation -2. Kprobes, Ftrace, Livepatching -3. Consistency model -4. Livepatch module - 4.1. New functions - 4.2. Metadata -5. Livepatch life-cycle - 5.1. Loading - 5.2. Enabling - 5.3. Replacing - 5.4. Disabling - 5.5. Removing -6. Sysfs -7. Limitations +.. Table of Contents: + + 1. Motivation + 2. Kprobes, Ftrace, Livepatching + 3. Consistency model + 4. Livepatch module + 4.1. New functions + 4.2. Metadata + 5. Livepatch life-cycle + 5.1. Loading + 5.2. Enabling + 5.3. Replacing + 5.4. Disabling + 5.5. Removing + 6. Sysfs + 7. Limitations 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, 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. - + 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 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 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 that may only be locally accessible. This can be solved by a special 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 @@ -258,7 +258,7 @@ Documentation/livepatch/module-elf-format.txt for more details. The patch is described by several structures that split the information 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 particular function. @@ -275,7 +275,7 @@ into three levels: only for a particular object ( vmlinux or a kernel module ). Note that 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 (NULL) or a module name. @@ -285,7 +285,7 @@ into three levels: 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). 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 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 -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 this process, see the "Consistency model" section. Finally, once all tasks have been patched, the 'transition' value changes 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 an entry to the list (see field `func_stack`) of the struct klp_ops. 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 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 @@ -421,7 +423,7 @@ See Documentation/ABI/testing/sysfs-kernel-livepatch for more details. 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 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 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. - + Kretprobes using the ftrace framework conflict with the patched + - Kretprobes using the ftrace framework conflict with the patched functions. 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. - + 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. There is a work in progress to add warnings about this situation. diff --git a/Documentation/livepatch/module-elf-format.txt b/Documentation/livepatch/module-elf-format.rst index f21a5289a09c..2a591e6f8e6c 100644 --- a/Documentation/livepatch/module-elf-format.txt +++ b/Documentation/livepatch/module-elf-format.rst @@ -4,33 +4,21 @@ Livepatch module Elf format This document outlines the Elf format requirements that livepatch modules must follow. ------------------ -Table of Contents ------------------ -0. Background and motivation -1. Livepatch modinfo field -2. Livepatch relocation sections - 2.1 What are livepatch relocation sections? - 2.2 Livepatch relocation section format - 2.2.1 Required flags - 2.2.2 Required name format - 2.2.3 Example livepatch relocation section names - 2.2.4 Example `readelf --sections` output - 2.2.5 Example `readelf --relocs` output -3. Livepatch symbols - 3.1 What are livepatch symbols? - 3.2 A livepatch module's symbol table - 3.3 Livepatch symbol format - 3.3.1 Required flags - 3.3.2 Required name format - 3.3.3 Example livepatch symbol names - 3.3.4 Example `readelf --symbols` output -4. Architecture-specific sections -5. Symbol table and Elf section access - ----------------------------- -0. Background and motivation ----------------------------- + +.. Table of Contents + + 1. Background and motivation + 2. Livepatch modinfo field + 3. Livepatch relocation sections + 3.1 Livepatch relocation section format + 4. Livepatch symbols + 4.1 A livepatch module's symbol table + 4.2 Livepatch symbol format + 5. Architecture-specific sections + 6. Symbol table and Elf section access + +1. Background and motivation +============================ Formerly, livepatch required separate architecture-specific code to write relocations. However, arch-specific code to write relocations already @@ -52,8 +40,8 @@ relocation sections and symbols, which are described in this document. The Elf constants used to mark livepatch symbols and relocation sections were selected from OS-specific ranges according to the definitions from glibc. -0.1 Why does livepatch need to write its own relocations? ---------------------------------------------------------- +Why does livepatch need to write its own relocations? +----------------------------------------------------- A typical livepatch module contains patched versions of functions that can reference non-exported global symbols and non-included local symbols. Relocations referencing these types of symbols cannot be left in as-is @@ -72,13 +60,8 @@ relas reference are special livepatch symbols (see section 2 and 3). The arch-specific livepatch relocation code is replaced by a call to apply_relocate_add(). -================================ -PATCH MODULE FORMAT REQUIREMENTS -================================ - --------------------------- -1. Livepatch modinfo field --------------------------- +2. Livepatch modinfo field +========================== Livepatch modules are required to have the "livepatch" modinfo attribute. See the sample livepatch module in samples/livepatch/ for how this is done. @@ -87,22 +70,23 @@ Livepatch modules can be identified by users by using the 'modinfo' command and looking for the presence of the "livepatch" field. This field is also used by the kernel module loader to identify livepatch modules. -Example modinfo output: ------------------------ -% modinfo livepatch-meminfo.ko -filename: livepatch-meminfo.ko -livepatch: Y -license: GPL -depends: -vermagic: 4.3.0+ SMP mod_unload - --------------------------------- -2. Livepatch relocation sections --------------------------------- - -------------------------------------------- -2.1 What are livepatch relocation sections? -------------------------------------------- +Example: +-------- + +**Modinfo output:** + +:: + + % modinfo livepatch-meminfo.ko + filename: livepatch-meminfo.ko + livepatch: Y + license: GPL + depends: + vermagic: 4.3.0+ SMP mod_unload + +3. Livepatch relocation sections +================================ + A livepatch module manages its own Elf relocation sections to apply relocations to modules as well as to the kernel (vmlinux) at the appropriate time. For example, if a patch module patches a driver that is @@ -127,12 +111,9 @@ Every symbol referenced by a rela in a livepatch relocation section is a livepatch symbol. These must be resolved before livepatch can call apply_relocate_add(). See Section 3 for more information. ---------------------------------------- -2.2 Livepatch relocation section format ---------------------------------------- +3.1 Livepatch relocation section format +======================================= -2.2.1 Required flags --------------------- Livepatch relocation sections must be marked with the SHF_RELA_LIVEPATCH section flag. See include/uapi/linux/elf.h for the definition. The module loader recognizes this flag and will avoid applying those relocation sections @@ -140,28 +121,39 @@ at patch module load time. These sections must also be marked with SHF_ALLOC, so that the module loader doesn't discard them on module load (i.e. they will be copied into memory along with the other SHF_ALLOC sections). -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 -^ ^^ ^ ^ ^ -|________||_____| |__________| - [A] [B] [C] + .klp.rela.objname.section_name + ^ ^^ ^ ^ ^ + |________||_____| |__________| + [A] [B] [C] -[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 - which the relocation section belongs follows immediately after the prefix. -[C] The actual name of the section to which this relocation section applies. +[A] + The relocation section name is prefixed with the string ".klp.rela." -2.2.3 Example livepatch relocation section names: -------------------------------------------------- -.klp.rela.ext4.text.ext4_attr_store -.klp.rela.vmlinux.text.cmdline_proc_show +[B] + The name of the object (i.e. "vmlinux" or name of module) to + which the relocation section belongs follows immediately after the prefix. + +[C] + The actual name of the section to which this relocation section applies. + +Examples: +--------- + +**Livepatch relocation section names:** + +:: + + .klp.rela.ext4.text.ext4_attr_store + .klp.rela.vmlinux.text.cmdline_proc_show + +**`readelf --sections` output for a patch +module that patches vmlinux and modules 9p, btrfs, ext4:** + +:: -2.2.4 Example `readelf --sections` output for a patch -module that patches vmlinux and modules 9p, btrfs, ext4: --------------------------------------------------------- Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ snip ] @@ -175,31 +167,33 @@ module that patches vmlinux and modules 9p, btrfs, ext4: [ snip ] ^ ^ | | [*] [*] -[*] 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 -not be discarded when the module is loaded into memory, as well as with the -SHF_RELA_LIVEPATCH flag ("o" - for OS-specific). - -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 -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. - --------------------- -3. Livepatch symbols --------------------- - -------------------------------- -3.1 What are livepatch symbols? -------------------------------- + +[*] + 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 + not be discarded when the module is loaded into memory, as well as with the + SHF_RELA_LIVEPATCH flag ("o" - for OS-specific). + +**`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 + 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. + +4. Livepatch symbols +==================== + Livepatch symbols are symbols referred to by livepatch relocation sections. These are symbols accessed from new versions of functions for patched objects, whose addresses cannot be resolved by the module loader (because @@ -219,9 +213,8 @@ loader can identify and ignore them. Livepatch modules keep these symbols in their symbol tables, and the symbol table is made accessible through module->symtab. -------------------------------------- -3.2 A livepatch module's symbol table -------------------------------------- +4.1 A livepatch module's symbol table +===================================== Normally, a stripped down copy of a module's symbol table (containing only "core" symbols) is made available through module->symtab (See layout_symtab() in kernel/module.c). For livepatch modules, the symbol table copied into memory @@ -231,71 +224,82 @@ relocation section refer to their respective symbols with their symbol indices, and the original symbol indices (and thus the symtab ordering) must be preserved in order for apply_relocate_add() to find the right symbol. -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 -in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the -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 ---------------------------- - -3.3.1 Required flags --------------------- +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 + in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the + 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 ] + +4.2 Livepatch symbol format +=========================== + Livepatch symbols must have their section index marked as SHN_LIVEPATCH, so that the module loader can identify them and not attempt to resolve them. See include/uapi/linux/elf.h for the actual definitions. -3.3.2 Required name format --------------------------- -Livepatch symbol names must conform to the following format: - -.klp.sym.objname.symbol_name,sympos -^ ^^ ^ ^ ^ ^ -|_______||_____| |_________| | - [A] [B] [C] [D] - -[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 - which the symbol belongs follows immediately after the prefix. -[C] The actual name of the symbol. -[D] The position of the symbol in the object (as according to kallsyms) - This is used to differentiate duplicate symbols within the same - object. The symbol position is expressed numerically (0, 1, 2...). - The symbol position of a unique symbol is 0. - -3.3.3 Example livepatch symbol names: -------------------------------------- -.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: ------------------------------------------------------------- -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 - 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 - [ snip ] ^ - | - [*] -[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20). - "OS" means OS-specific. - ---------------------------------- -4. Architecture-specific sections ---------------------------------- +Livepatch symbol names must conform to the following format:: + + .klp.sym.objname.symbol_name,sympos + ^ ^^ ^ ^ ^ ^ + |_______||_____| |_________| | + [A] [B] [C] [D] + +[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 + which the symbol belongs follows immediately after the prefix. + +[C] + The actual name of the symbol. + +[D] + The position of the symbol in the object (as according to kallsyms) + This is used to differentiate duplicate symbols within the same + object. The symbol position is expressed numerically (0, 1, 2...). + The symbol position of a unique symbol is 0. + +Examples: +--------- + +**Livepatch symbol names:** + +:: + + .klp.sym.vmlinux.snprintf,0 + .klp.sym.vmlinux.printk,0 + .klp.sym.btrfs.btrfs_ktype,0 + +**`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 + 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 + [ snip ] ^ + | + [*] + +[*] + Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20). + "OS" means OS-specific. + +5. Architecture-specific sections +================================= Architectures may override arch_klp_init_object_loaded() to perform additional arch-specific tasks when a target module loads, such as applying arch-specific sections. On x86 for example, we must apply per-object @@ -304,20 +308,19 @@ These sections must be prefixed with ".klp.arch.$objname." so that they can be easily identified when iterating through a patch module's Elf sections (See arch/x86/kernel/livepatch.c for a complete example). --------------------------------------- -5. Symbol table and Elf section access --------------------------------------- +6. Symbol table and Elf section access +====================================== A livepatch module's symbol table is accessible through module->symtab. Since apply_relocate_add() requires access to a module's section headers, symbol table, and relocation section indices, Elf information is preserved for 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, -this struct is filled in by the module loader. Its fields are documented below: - -struct klp_modinfo { - Elf_Ehdr hdr; /* Elf header */ - Elf_Shdr *sechdrs; /* Section header table */ - char *secstrings; /* String table for the section headers */ - unsigned int symndx; /* The symbol table section index */ -}; +this struct is filled in by the module loader. Its fields are documented below:: + + struct klp_modinfo { + Elf_Ehdr hdr; /* Elf header */ + Elf_Shdr *sechdrs; /* Section header table */ + char *secstrings; /* String table for the section headers */ + unsigned int symndx; /* The symbol table section index */ + }; diff --git a/Documentation/livepatch/shadow-vars.txt b/Documentation/livepatch/shadow-vars.rst index ecc09a7be5dd..c05715aeafa4 100644 --- a/Documentation/livepatch/shadow-vars.txt +++ b/Documentation/livepatch/shadow-vars.rst @@ -27,10 +27,13 @@ A hashtable references all shadow variables. These references are stored and retrieved through a <obj, id> pair. * The klp_shadow variable data structure encapsulates both tracking -meta-data and shadow-data: + meta-data and shadow-data: + - meta-data + - obj - pointer to parent object - id - data identifier + - data[] - storage for shadow data 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 - search hashtable for <obj, id> pair + - if exists + - WARN and return NULL + - if <obj, id> doesn't already exist + - allocate a new shadow variable - initialize the variable using a custom constructor and data when provided - add <obj, id> to the global hashtable * klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable - search hashtable for <obj, id> pair + - if exists + - return existing shadow variable + - if <obj, id> doesn't already exist + - allocate a new shadow variable - initialize the variable using a custom constructor and data when provided - add <obj, id> pair to the global hashtable * klp_shadow_free() - detach and free a <obj, id> shadow variable - find and remove a <obj, id> reference from global hashtable + - if found + - call destructor function if defined - free shadow variable * klp_shadow_free_all() - detach and free all <*, id> shadow variables - find and remove any <*, id> references from global hashtable + - if found + - call destructor function if defined - 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 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 -struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata, - const u8 *addr, gfp_t gfp) -{ + #define PS_LOCK 1 + struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata, + const u8 *addr, gfp_t gfp) + { struct sta_info *sta; 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 -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; /* 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 -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); 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. 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; spin_lock_init(lock); return 0; -} + } -#define PS_LOCK 1 -void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta) -{ + #define PS_LOCK 1 + void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta) + { spinlock_t *ps_lock; /* sync with ieee80211_tx_h_unicast_ps_buf */ @@ -200,10 +215,12 @@ suggests how to handle the parent object. ============= * 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 -Dynamic and Adaptive Updates of Non-Quiescent Subsystems in Commodity -Operating System Kernels (Kritis Makris, Kyung Dong Ryu 2007) presented -a datatype update technique called "shadow data structures". + + Dynamic and Adaptive Updates of Non-Quiescent Subsystems in Commodity + Operating System Kernels (Kritis Makris, Kyung Dong Ryu 2007) presented + a datatype update technique called "shadow data structures". |