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

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Message-ID: <20151201084858.GB3974@packer-debian-8-amd64.digitalocean.com>
Date:	Tue, 1 Dec 2015 03:48:59 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	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>
Cc:	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

+++ Jessica Yu [30/11/15 23:21 -0500]:
>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
>
> 	/* The command line arguments (may be mangled).  People like
>@@ -461,6 +469,7 @@ struct module {
> #endif
>
> #ifdef CONFIG_LIVEPATCH
>+	bool klp; /* Is this a livepatch module? */

Gah. I believe this field should be outside the #ifdef. 

Jessica
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