Re: [PATCH v6 1/3] Add a new ima hook ima_kexec_cmdline to measure cmdline args

[Mimi Zohar]

Hi Prakhar,

On Mon, 2019-05-20 at 17:06 -0700, Prakhar Srivastava wrote:
> Currently during kexec_file_load(soft reboot) the cmdline args
> passed are not measured and the PCR values are not reset.

This patch addresses not measuring the kexec boot cmdline. ÂI don't
see a reason for mentioning anything about the PCR values not being
reset. ÂKeep it simple.

> This results in the new kernel to assume a secure boot was
> followed. The boot args used to launch the new kernel need to be
> measured and carried over to the next kernel to be used for
> attestation. IMA supports only measuring files, no functionality
> exists to measure a buffer(kexec cmdline).
> 
> This change adds a new functionality to measure buffers
> process_buffer_measurement which uses the hash of the buffer
> instead of file hash to add an entry in the ima log.
> A new ima hook ima_kexec_cmdline is also defined which calls
> into process_buffer_measurement to add the kexec_cmdline args
> to the log.
> 
> A new policy KEXEC_CMDLINE is also defined to control measuring the
> kexec_cmdline buffer.
> This patch only adds IMA_MEASURE as a supported functionality.
> 
> - A new ima hook ima_kexec_cmdline is defined to be called by the
> kexec code.
> - A new function process_buffer_measurement is defined to measure
> the buffer hash into the ima log.
> - A new func policy KEXEC_CMDLINE is defined to control the measurement.

Missing is how to verify the digest of the measurement list kexec boot
cmdline entry based on /proc/cmdline. ÂEverything before the "root="
in the /proc entry needs to be removed before calculating the hash.
ÂPlease include a sample shell command.

Matthew's patch "IMA: Allow profiles to define the desired IMA
template" will require changes to this patch. ÂPlease rebase this
patch set on top of it, once Matthew addresses the comments and re-
posts.

(Reminder: the patch description should be 70 - 75 characters.)

> 
> Signed-off-by: Prakhar Srivastava <prsriva02@xxxxxxxxx>
> ---

< snip >

> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -576,6 +576,83 @@ int ima_load_data(enum kernel_load_data_id id)
>  	return 0;
>  }
>  
> +/*
> + * process_buffer_measurement - Measure the buffer to ima log.
> + * @buf: pointer to the buffer that needs to be added to the log.
> + * @size: size of buffer(in bytes).
> + * @eventname: event name to be used for the buffer entry.
> + * @cred: a pointer to a credentials structure for user validation.
> + * @secid: the secid of the task to be validated.
> + *
> + * Based on policy, the buffer is measured into the ima log.
> + */
> +static void process_buffer_measurement(const void *buf, int size,
> +				const char *eventname, const struct cred *cred,
> +				u32 secid)
> +{
> +	int ret = 0;
> +	struct ima_template_entry *entry = NULL;
> +	struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
> +	struct ima_event_data event_data = {iint, NULL, NULL,
> +						NULL, 0, NULL};

Thiago's clean up patch initializes only specific variables, as
needed. ÂPlease initialize event_data like:

struct ima_event_data event_data = {.iint = iint};


> +	struct {
> +		struct ima_digest_data hdr;
> +		char digest[IMA_MAX_DIGEST_SIZE];
> +	} hash;
> +	int violation = 0;
> +	int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
> +	int action = 0;
> +
> +	action = ima_get_action(NULL, cred, secid, 0, KEXEC_CMDLINE, &pcr);
> +	if (!(action & IMA_MEASURE))
> +		goto out;
> +
> +	memset(iint, 0, sizeof(*iint));
> +	memset(&hash, 0, sizeof(hash));
> +
> +	event_data.filename = eventname;
> +
> +	iint->ima_hash = &hash.hdr;
> +	iint->ima_hash->algo = ima_hash_algo;
> +	iint->ima_hash->length = hash_digest_size[ima_hash_algo];
> +
> +	ret = ima_calc_buffer_hash(buf, size, iint->ima_hash);
> +	if (ret < 0)
> +		goto out;
> +
> +	ret = ima_alloc_init_template(&event_data, &entry);
> +	if (ret < 0)
> +		goto out;
> +
> +	if (action & IMA_MEASURE)
> +		ret = ima_store_template(entry, violation, NULL, buf, pcr);
> +
> +	if (ret < 0) {
> +		ima_free_template_entry(entry);
> +	}

Remove brackets.

Mimi

> +
> +out:
> +	return;
> +}