Subject: Re: [PATCH 1/7] ima: on soft reboot, restore the measurement list

From: Petko Manolov <[email-masked]>
Date: Fri, 5 Aug 2016 11:44:25 +0300

On 16-08-04 08:24:29, Mimi Zohar wrote:
> The TPM PCRs are only reset on a hard reboot.  In order to validate a
> TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
> of the running kernel must be saved and restored on boot.  This patch
> restores the measurement list.
> 
> Changelog:
> - call ima_load_kexec_buffer() (Thiago)
> 
> Signed-off-by: Mimi Zohar <[email-masked]>
> ---
>  security/integrity/ima/Makefile       |   1 +
>  security/integrity/ima/ima.h          |  10 ++
>  security/integrity/ima/ima_init.c     |   2 +
>  security/integrity/ima/ima_kexec.c    |  55 +++++++++++
>  security/integrity/ima/ima_queue.c    |  10 ++
>  security/integrity/ima/ima_template.c | 171 ++++++++++++++++++++++++++++++++++
>  6 files changed, 249 insertions(+)
>  create mode 100644 security/integrity/ima/ima_kexec.c
> 
> diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
> index c34599f..c0ce7b1 100644
> --- a/security/integrity/ima/Makefile
> +++ b/security/integrity/ima/Makefile
> @@ -8,4 +8,5 @@ obj-$(CONFIG_IMA) += ima.o
>  ima-y := ima_fs.o ima_queue.o ima_init.o ima_main.o ima_crypto.o ima_api.o \
>  	 ima_policy.o ima_template.o ima_template_lib.o ima_buffer.o
>  ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
> +ima-$(CONFIG_KEXEC_FILE) += ima_kexec.o
>  obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index b5728da..84e8d36 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -102,6 +102,13 @@ struct ima_queue_entry {
>  };
>  extern struct list_head ima_measurements;	/* list of all measurements */
>  
> +/* Some details preceding the binary serialized measurement list */
> +struct ima_kexec_hdr {
> +	unsigned short version;
> +	unsigned long buffer_size;
> +	unsigned long count;
> +} __packed;

Unless there is no real need for this structure to be packed i suggest dropping 
the attribute.  When referenced through pointer 32bit ARM and MIPS (and likely 
all other 32bit RISC CPUs) use rather inefficient byte loads and stores.

Worse, if, for example, ->count is going to be read/written concurrently from 
multiple threads we get torn loads/stores thus losing atomicity of the access.

		Petko