linux-kernel - Re: [PATCH 12/18] Hibernate: generate and verify signature of snapshot

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Message-ID: <20130825163648.GI5171@amd.pavel.ucw.cz>
Date:	Sun, 25 Aug 2013 18:36:48 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-crypto@...r.kernel.org,
	opensuse-kernel@...nsuse.org, David Howells <dhowells@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <len.brown@...el.com>,
	Josh Boyer <jwboyer@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Matt Fleming <matt.fleming@...el.com>,
	James Bottomley <james.bottomley@...senpartnership.com>,
	Greg KH <gregkh@...uxfoundation.org>, JKosina@...e.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Gary Lin <GLin@...e.com>, Vivek Goyal <vgoyal@...hat.com>,
	"Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH 12/18] Hibernate: generate and verify signature of
 snapshot

On Thu 2013-08-22 19:01:51, Lee, Chun-Yi wrote:
> This patch add the code for generate/verify signature of snapshot, it
> put the signature to snapshot header. This approach can support both
> on userspace hibernate and in-kernel hibernate.
> 
> v2:
> - Due to loaded S4 sign key before ExitBootServices, we need forward key from
>   boot kernel to resume target kernel. So this patch add a empty page in
>   snapshot image, then we keep the pfn of this empty page in snapshot header.
>   When system resume from hibernate, we fill new sign key to this empty page
>   space after snapshot image checked pass. This mechanism let boot kernel can
>   forward new sign key to resume target kernel but don't need write new private
>   key to any other storage, e.g. swap.
> 
> Cc: Matthew Garrett <mjg59@...f.ucam.org>
> Reviewed-by: Jiri Kosina <jkosina@...e.cz>
> Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> ---
>  kernel/power/power.h    |    6 +
>  kernel/power/snapshot.c |  280 +++++++++++++++++++++++++++++++++++++++++++++-
>  kernel/power/swap.c     |   14 +++
>  kernel/power/user.c     |    9 ++
>  4 files changed, 302 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/power/power.h b/kernel/power/power.h
> index 69a81d8..84e0b06 100644
> --- a/kernel/power/power.h
> +++ b/kernel/power/power.h
> @@ -3,6 +3,9 @@
>  #include <linux/utsname.h>
>  #include <linux/freezer.h>
>  
> +/* The maximum length of snapshot signature */
> +#define SIG_LENG 512
> +
>  struct swsusp_info {
>  	struct new_utsname	uts;
>  	u32			version_code;
> @@ -11,6 +14,8 @@ struct swsusp_info {
>  	unsigned long		image_pages;
>  	unsigned long		pages;
>  	unsigned long		size;
> +	unsigned long           skey_data_buf_pfn;
> +	u8			signature[SIG_LENG];
>  } __attribute__((aligned(PAGE_SIZE)));

SIG_LEN or SIG_LENGTH. Select one.


> +static int
>  copy_data_pages(struct memory_bitmap *copy_bm, struct memory_bitmap *orig_bm)
>  {
>  	struct zone *zone;
> -	unsigned long pfn;
> +	unsigned long pfn, dst_pfn;
...
> +	tfm = crypto_alloc_shash(SNAPSHOT_HASH, 0, 0);
> +	if (IS_ERR(tfm)) {
> +		pr_err("IS_ERR(tfm): %ld", PTR_ERR(tfm));
> +		return PTR_ERR(tfm);
> +	}
> +
> +	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
> +	digest_size = crypto_shash_digestsize(tfm);
> +	digest = kzalloc(digest_size + desc_size, GFP_KERNEL);

Are you sure GFP_KERNEL allocation is okay at this phase of
hibernation?

Could the hashing be done at later phase, when writing the image to
disk?

>  
> +void **h_buf;

helpfully named.

> +	ret = verify_signature(s4_wake_key, pks);
> +	if (ret) {
> +		pr_err("snapshot S4 signature verification fail: %d\n", ret);
> +		goto error_verify;
> +	} else
> +		pr_info("snapshot S4 signature verification pass!\n");
> +
> +	if (pks->rsa.s)
> +		mpi_free(pks->rsa.s);
> +	kfree(pks);

ret = 0 and fall through?

> +	return 0;
> +
> +error_verify:
> +	if (pks->rsa.s)
> +		mpi_free(pks->rsa.s);
> +error_mpi:
> +	kfree(pks);
> +	return ret;
> +}


> +	ret = crypto_shash_final(desc, digest);
> +	if (ret)
> +		goto error_shash;
> +
> +	ret = snapshot_verify_signature(digest, digest_size);
> +	if (ret)
> +		goto error_verify;
> +
> +	kfree(h_buf);
> +	kfree(digest);
> +	crypto_free_shash(tfm);
> +	return 0;

These four lines can be deleted.

> +
> +error_verify:
> +error_shash:
> +	kfree(h_buf);
> +	kfree(digest);
> +error_digest:
> +	crypto_free_shash(tfm);
> +	return ret;
> +}
> +
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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