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authorPeter Zijlstra <peterz@infradead.org>2020-04-29 10:24:45 -0500
committerJiri Kosina <jkosina@suse.cz>2020-05-08 00:12:42 +0200
commit1d05334d2899bd3ecdf01beb53f0a70884a7f471 (patch)
treeb6e55679f1261a26b7c590c1f2542b1667cd90d0 /Documentation/livepatch
parent7c8e2bdd5f0d990e2398ee3deafc626dd469fc2d (diff)
livepatch: Remove .klp.arch
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) <peterz@infradead.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Joe Lawrence <joe.lawrence@redhat.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'Documentation/livepatch')
-rw-r--r--Documentation/livepatch/module-elf-format.rst15
1 files changed, 2 insertions, 13 deletions
diff --git a/Documentation/livepatch/module-elf-format.rst b/Documentation/livepatch/module-elf-format.rst
index 2a591e6f8e6c..8c6b894c4661 100644
--- a/Documentation/livepatch/module-elf-format.rst
+++ b/Documentation/livepatch/module-elf-format.rst
@@ -14,8 +14,7 @@ This document outlines the Elf format requirements that livepatch modules must f
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
+ 5. Symbol table and Elf section access
1. Background and motivation
============================
@@ -298,17 +297,7 @@ Examples:
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
-.altinstructions and .parainstructions sections when a target module loads.
-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).
-
-6. Symbol table and Elf section access
+5. Symbol table and Elf section access
======================================
A livepatch module's symbol table is accessible through module->symtab.