linux-kernel - Re: module: preserve Elf information for livepatch modules

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Date:	Mon, 21 Dec 2015 00:44:20 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Miroslav Benes <mbenes@...e.cz>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: module: preserve Elf information for livepatch modules

+++ Petr Mladek [17/12/15 17:26 +0100]:
>On Mon 2015-11-30 23:21:15, Jessica Yu wrote:
>> For livepatch modules, copy Elf section, symbol, and string information
>> from the load_info struct in the module loader.
>>
>> Livepatch uses special relocation sections in order to be able to patch
>> modules that are not yet loaded, as well as apply patches to the kernel
>> when the addresses of symbols cannot be determined at compile time (for
>> example, when kaslr is enabled). Livepatch modules must preserve Elf
>> information such as section indices in order to apply the remaining
>> relocation sections at the appropriate time (i.e. when the target module
>> loads).
>>
>> Signed-off-by: Jessica Yu <jeyu@...hat.com>
>> ---
>>  include/linux/module.h |  9 +++++
>>  kernel/module.c        | 98 ++++++++++++++++++++++++++++++++++++++++++++++++--
>>  2 files changed, 105 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/module.h b/include/linux/module.h
>> index 3a19c79..9b46256 100644
>> --- a/include/linux/module.h
>> +++ b/include/linux/module.h
>> @@ -425,6 +425,14 @@ struct module {
>>
>>  	/* Notes attributes */
>>  	struct module_notes_attrs *notes_attrs;
>> +
>> +	/* Elf information (optionally saved) */
>> +	Elf_Ehdr *hdr;
>> +	Elf_Shdr *sechdrs;
>> +	char *secstrings;
>> +	struct {
>> +		unsigned int sym, str, mod, vers, info, pcpu;
>> +	} index;
>>  #endif
>
>I would hide this into a structure. It is 3 pointers and 6 integers
>that are mostly unused. I think about using a pointer to struct load_info
>here. We could set the unused stuff to zero and NULL.
>
>Any better idea how to share the definition with struct load_info
>is welcome.

Sure. If we want to encapsulate all this information, we can perhaps
replace this with a single pointer to a copy of load_info, and maybe
move the struct definition of load_info to module.h.

Jessica
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