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Message-ID: <20151221054420.GA22850@packer-debian-8-amd64.digitalocean.com>
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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