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module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD 

Dynamic code patching (alternatives, jump_label and static_call) can
have sites in __exit code, even it __exit is never executed. Therefore
__exit must be present at runtime, at least for as long as __init code
is.

Additionally, for jump_label and static_call, the __exit sites must also
identify as within_module_init(), such that the infrastructure is aware
to never touch them after module init -- alternatives are only ran once
at init and hence don't have this particular constraint.

By making __exit identify as __init for MODULE_UNLOAD, the above is
satisfied.

So, when !CONFIG_MODULE_UNLOAD, the section ordering should look like the
following, with the .exit sections moved to the init region of the module.

Core section allocation order:
 	.text
 	.rodata
 	__ksymtab_gpl
 	__ksymtab_strings
 	.note.* sections
 	.bss
 	.data
 	.gnu.linkonce.this_module
 Init section allocation order:
 	.init.text
 	.exit.text
 	.symtab
 	.strtab

[jeyu: thanks to Peter Zijlstra for most of changelog]

Link: https://lore.kernel.org/lkml/YFiuphGw0RKehWsQ@gunter/
Link: https://lore.kernel.org/r/20210323142756.11443-1-jeyu@kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
This commit is contained in:
Jessica Yu 2021-03-23 13:15:41 +01:00
parent 1e28eed176
commit 33121347fb
1 changed files with 4 additions and 5 deletions
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9
kernel/module.c
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@ -2802,7 +2802,11 @@ void * __weak module_alloc(unsigned long size)
bool __weak module_init_section(const char *name)
{
#ifndef CONFIG_MODULE_UNLOAD
return strstarts(name, ".init") || module_exit_section(name);
#else
return strstarts(name, ".init");
#endif
}
bool __weak module_exit_section(const char *name)
@ -3116,11 +3120,6 @@ static int rewrite_section_headers(struct load_info *info, int flags)
*/
shdr->sh_addr = (size_t)info->hdr + shdr->sh_offset;
#ifndef CONFIG_MODULE_UNLOAD
/* Don't load .exit sections */
if (module_exit_section(info->secstrings+shdr->sh_name))
shdr->sh_flags &= ~(unsigned long)SHF_ALLOC;
#endif
}
/* Track but don't keep modinfo and version sections. */