Kernel-hardening Archive on lore.kernel.org
 help / color / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, arjan@linux.intel.com, rick.p.edgecombe@intel.com,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	kernel-hardening@lists.openwall.com, Jessica Yu <jeyu@kernel.org>
Subject: Re: [RFC PATCH 10/11] module: Reorder functions
Date: Thu, 6 Feb 2020 04:41:46 -0800
Message-ID: <202002060440.E7ED91B@keescook> (raw)
In-Reply-To: <20200205223950.1212394-11-kristen@linux.intel.com>

On Wed, Feb 05, 2020 at 02:39:49PM -0800, Kristen Carlson Accardi wrote:
> If a module has functions split out into separate text sections
> (i.e. compiled with the -ffunction-sections flag), reorder the
> functions to provide some code diversification to modules.
> 
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>

Probably a good idea to add Jessica to CC in next version:
	Jessica Yu <jeyu@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  kernel/module.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 85 insertions(+)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index b56f3224b161..231563e95e61 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -53,6 +53,8 @@
>  #include <linux/bsearch.h>
>  #include <linux/dynamic_debug.h>
>  #include <linux/audit.h>
> +#include <linux/random.h>
> +#include <asm/setup.h>
>  #include <uapi/linux/module.h>
>  #include "module-internal.h"
>  
> @@ -3245,6 +3247,87 @@ static int find_module_sections(struct module *mod, struct load_info *info)
>  	return 0;
>  }
>  
> +/*
> + * shuffle_text_list()
> + * Use a Fisher Yates algorithm to shuffle a list of text sections.
> + */
> +static void shuffle_text_list(Elf_Shdr **list, int size)
> +{
> +	int i;
> +	unsigned int j;
> +	Elf_Shdr *temp;
> +
> +	for (i = size - 1; i > 0; i--) {
> +		/*
> +		 * TBD - seed. We need to be able to use a known
> +		 * seed so that we can non-randomly randomize for
> +		 * debugging.
> +		 */
> +
> +		// pick a random index from 0 to i
> +		get_random_bytes(&j, sizeof(j));
> +		j = j % (i + 1);
> +
> +		temp = list[i];
> +		list[i] = list[j];
> +		list[j] = temp;
> +	}
> +}
> +
> +/*
> + * randomize_text()
> + * Look through the core section looking for executable code sections.
> + * Store sections in an array and then shuffle the sections
> + * to reorder the functions.
> + */
> +static void randomize_text(struct module *mod, struct load_info *info)
> +{
> +	int i;
> +	int num_text_sections = 0;
> +	Elf_Shdr **text_list;
> +	int size = 0;
> +	int max_sections = info->hdr->e_shnum;
> +	unsigned int sec = find_sec(info, ".text");
> +
> +	if (!IS_ENABLED(CONFIG_FG_KASLR) || !kaslr_enabled())
> +		return;
> +
> +	if (sec == 0)
> +		return;
> +
> +	text_list = kmalloc_array(max_sections, sizeof(*text_list), GFP_KERNEL);
> +	if (text_list == NULL)
> +		return;
> +
> +	for (i = 0; i < max_sections; i++) {
> +		Elf_Shdr *shdr = &info->sechdrs[i];
> +		const char *sname = info->secstrings + shdr->sh_name;
> +
> +		if (!(shdr->sh_flags & SHF_ALLOC) ||
> +		    !(shdr->sh_flags & SHF_EXECINSTR) ||
> +		    strstarts(sname, ".init"))
> +			continue;
> +
> +		text_list[num_text_sections] = shdr;
> +		num_text_sections++;
> +	}
> +
> +	shuffle_text_list(text_list, num_text_sections);
> +
> +	for (i = 0; i < num_text_sections; i++) {
> +		Elf_Shdr *shdr = text_list[i];
> +		unsigned int infosec;
> +		const char *sname;
> +
> +		sname = info->secstrings + shdr->sh_name;
> +		infosec	= shdr->sh_info;
> +
> +		shdr->sh_entsize = get_offset(mod, &size, shdr, infosec);
> +	}
> +
> +	kfree(text_list);
> +}
> +
>  static int move_module(struct module *mod, struct load_info *info)
>  {
>  	int i;
> @@ -3282,6 +3365,8 @@ static int move_module(struct module *mod, struct load_info *info)
>  	} else
>  		mod->init_layout.base = NULL;
>  
> +	randomize_text(mod, info);
> +
>  	/* Transfer each section which specifies SHF_ALLOC */
>  	pr_debug("final section addresses:\n");
>  	for (i = 0; i < info->hdr->e_shnum; i++) {
> -- 
> 2.24.1
> 

-- 
Kees Cook

  reply index

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-05 22:39 [RFC PATCH 00/11] Finer grained kernel address space randomization Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 01/11] modpost: Support >64K sections Kristen Carlson Accardi
2020-02-06 12:38   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 02/11] x86: tools/relocs: Support >64K section headers Kristen Carlson Accardi
2020-02-06 12:39   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 03/11] x86/boot: Allow a "silent" kaslr random byte fetch Kristen Carlson Accardi
2020-02-06  1:08   ` Andy Lutomirski
2020-02-06 11:48     ` Kees Cook
2020-02-06 16:58     ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 04/11] x86/boot/KASLR: Introduce PRNG for faster shuffling Kristen Carlson Accardi
2020-02-06  1:11   ` Andy Lutomirski
2020-02-06 15:10   ` Jason A. Donenfeld
2020-02-07  7:23     ` Jean-Philippe Aumasson
2020-02-07  9:05       ` Kees Cook
2020-02-07 16:52         ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Kristen Carlson Accardi
2020-02-06 10:30   ` Peter Zijlstra
2020-02-06 11:52     ` Kees Cook
2020-02-25 17:55   ` Arvind Sankar
2020-02-26 19:13     ` Kristen Carlson Accardi
2020-03-24 21:24     ` Kristen Carlson Accardi
2020-03-25 15:34       ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 06/11] x86: make sure _etext includes function sections Kristen Carlson Accardi
2020-02-06 12:26   ` Kees Cook
2020-02-06 13:15     ` Jann Horn
2020-02-06 16:27       ` David Laight
2020-02-06 14:39     ` Arvind Sankar
2020-02-06 15:29       ` Arvind Sankar
2020-02-06 16:11         ` Andy Lutomirski
2020-02-06 14:57     ` Arvind Sankar
2020-02-06 15:45       ` Arvind Sankar
2020-02-06 19:41     ` Kristen Carlson Accardi
2020-02-06 20:02       ` Andy Lutomirski
2020-02-07  9:24         ` Peter Zijlstra
2020-02-10  1:43           ` Kees Cook
2020-02-10 10:51             ` Peter Zijlstra
2020-02-10 15:54               ` Arjan van de Ven
2020-02-10 16:36                 ` Arvind Sankar
2020-02-21 19:50                   ` Josh Poimboeuf
2020-02-21 23:05                     ` Arvind Sankar
2020-02-05 22:39 ` [RFC PATCH 07/11] x86/tools: Adding relative relocs for randomized functions Kristen Carlson Accardi
2020-02-06 12:37   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 08/11] x86: Add support for finer grained KASLR Kristen Carlson Accardi
2020-02-06  1:17   ` Andy Lutomirski
2020-02-06 11:56     ` Kees Cook
2020-02-06 17:36       ` Kristen Carlson Accardi
2020-02-06 10:38   ` Peter Zijlstra
2020-02-06 12:06     ` Kees Cook
2020-02-06 14:52       ` Peter Zijlstra
2020-02-06 17:25         ` Kristen Carlson Accardi
2020-02-06 17:35           ` Peter Zijlstra
2020-02-06 17:43             ` Kristen Carlson Accardi
2020-02-25 17:49   ` Arvind Sankar
2020-02-26 19:26     ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 09/11] kallsyms: hide layout and expose seed Kristen Carlson Accardi
2020-02-06 12:32   ` Kees Cook
2020-02-06 17:51     ` Kristen Carlson Accardi
2020-02-06 19:27       ` Jann Horn
2020-03-02 19:01         ` Kristen Carlson Accardi
2020-03-02 19:08           ` Kees Cook
2020-03-02 19:19             ` Kristen Carlson Accardi
2020-02-27  2:42       ` Baoquan He
2020-02-27 16:02         ` Kees Cook
2020-02-28  3:36           ` Baoquan He
2020-02-05 22:39 ` [RFC PATCH 10/11] module: Reorder functions Kristen Carlson Accardi
2020-02-06 12:41   ` Kees Cook [this message]
2020-02-11 12:39     ` Jessica Yu
2020-02-05 22:39 ` [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss Kristen Carlson Accardi
2020-02-06  0:11   ` Arvind Sankar
2020-02-06  0:33     ` Kristen Carlson Accardi
2020-02-06 11:13     ` Kees Cook
2020-02-06 14:25       ` Arvind Sankar
2020-02-06 21:32         ` Kees Cook

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=202002060440.E7ED91B@keescook \
    --to=keescook@chromium.org \
    --cc=arjan@linux.intel.com \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=jeyu@kernel.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=kristen@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=rick.p.edgecombe@intel.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Kernel-hardening Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kernel-hardening/0 kernel-hardening/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kernel-hardening kernel-hardening/ https://lore.kernel.org/kernel-hardening \
		kernel-hardening@lists.openwall.com
	public-inbox-index kernel-hardening

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/com.openwall.lists.kernel-hardening


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git