Re: [PATCH v5 1/8] ima: define and call ima_alloc_kexec_file_buf

[Mimi Zohar <zohar@linux.ibm.com>]

On Wed, 2024-02-14 at 07:38 -0800, Tushar Sugandhi wrote:
> Carrying the IMA measurement list across kexec requires allocating a
> buffer and copying the measurement records.  Separate allocating the
> buffer and copying the measurement records into separate functions in
> order to allocate the buffer at kexec 'load' and copy the measurements
> at kexec 'execute'.
> 
> This patch includes the following changes:
>  - Refactor ima_dump_measurement_list() to move the memory allocation
>    to a separate function ima_alloc_kexec_file_buf() which allocates
>    buffer of size 'kexec_segment_size' at kexec 'load'.
>  - Make the local variable ima_kexec_file in ima_dump_measurement_list()
>    as local static to the file, so that it can be accessed from 
>    ima_alloc_kexec_file_buf().
>  - Make necessary changes to the function ima_add_kexec_buffer() to call
>    the above two functions.
> 
> Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> ---
>  security/integrity/ima/ima_kexec.c | 107 +++++++++++++++++++++--------
>  1 file changed, 78 insertions(+), 29 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_kexec.c
> b/security/integrity/ima/ima_kexec.c
> index dadc1d138118..a9cb5e882e2e 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -15,62 +15,98 @@
>  #include "ima.h"
>  
>  #ifdef CONFIG_IMA_KEXEC
> +static struct seq_file ima_kexec_file;
> +
> +static void ima_reset_kexec_file(struct seq_file *sf)
> +{
> +	sf->buf = NULL;
> +	sf->size = 0;
> +	sf->read_pos = 0;
> +	sf->count = 0;
> +}
> +
> +static void ima_free_kexec_file_buf(struct seq_file *sf)
> +{
> +	vfree(sf->buf);
> +	ima_reset_kexec_file(sf);
> +}
> +
> +static int ima_alloc_kexec_file_buf(size_t segment_size)
> +{
> +	/*
> +	 * kexec 'load' may be called multiple times.
> +	 * Free and realloc the buffer only if the segment_size is
> +	 * changed from the previous kexec 'load' call.
> +	 */
> +	if (ima_kexec_file.buf &&
> +	    ima_kexec_file.size == segment_size &&
> +	    ima_kexec_file.read_pos == 0 &&
> +	    ima_kexec_file.count == sizeof(struct ima_kexec_hdr))
> +		return 0;

ima_kexec_file.size will be initialized to zero.  No need to test anything other
than the segment size.

> +
> +	ima_free_kexec_file_buf(&ima_kexec_file);

The first time ima_free_kexec_file_buf() is called the memory has not been
allocated.  Test that the memory has been allocated before freeing it.  Since
there's no other ima_free_kexec_file_buf() caller, there's no need to clear the
other fields as they will be set below.

> +
> +	/* segment size can't change between kexec load and execute */
> +	ima_kexec_file.buf = vmalloc(segment_size);
> +	if (!ima_kexec_file.buf)
> +		return -ENOMEM;
> +
> +	ima_kexec_file.size = segment_size;
> +	ima_kexec_file.read_pos = 0;

static variables are initialized to zero.  No need to set it here.

> +	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved
> space */
> +
> +	return 0;
> +}
> +
>  static int ima_dump_measurement_list(unsigned long *buffer_size, void
> **buffer,
>  				     unsigned long segment_size)
>  {
>  	struct ima_queue_entry *qe;
> -	struct seq_file file;
>  	struct ima_kexec_hdr khdr;
> -	int ret = 0;
>  
> -	/* segment size can't change between kexec load and execute */
> -	file.buf = vmalloc(segment_size);
> -	if (!file.buf) {
> -		ret = -ENOMEM;
> -		goto out;
> +	if (!ima_kexec_file.buf) {
> +		*buffer_size = 0;
> +		*buffer = NULL;
> +		pr_err("%s: Kexec file buf not allocated\n", __func__);
> +		return -EINVAL;
>  	}
>  
> -	file.size = segment_size;
> -	file.read_pos = 0;
> -	file.count = sizeof(khdr);	/* reserved space */
> -
>  	memset(&khdr, 0, sizeof(khdr));
>  	khdr.version = 1;
> +
> +	/* Copy as many IMA measurements list records as possible */
>  	list_for_each_entry_rcu(qe, &ima_measurements, later) {
> -		if (file.count < file.size) {
> +		if (ima_kexec_file.count < ima_kexec_file.size) {

With an extra half page memory allocated, there should be enough memory for a
few extra records as a result of the kexec load.  Subsequent patches are going
to change this assumption.  This test doesn't ensure there is enough memory for
the entire measurement record.  Call get_binary_runtime_size() to get the record
size to ensure there is enough memory for the entire record.

>  			khdr.count++;
> -			ima_measurements_show(&file, qe);
> +			ima_measurements_show(&ima_kexec_file, qe);
>  		} else {
> -			ret = -EINVAL;
> +			pr_err("%s: IMA log file is too big for Kexec buf\n",
> +			       __func__);

This message and the one above should probably be pr_debug().  There's a new
error message after the call to ima_dump_measurement_list().

>  			break;
>  		}
>  	}
>  
> -	if (ret < 0)
> -		goto out;
> -

Removing these lines is in for "copying as many measurements as possible". That
change isn't mentioned in the patch description.

>  	/*
>  	 * fill in reserved space with some buffer details
>  	 * (eg. version, buffer size, number of measurements)
>  	 */
> -	khdr.buffer_size = file.count;
> +	khdr.buffer_size = ima_kexec_file.count;
>  	if (ima_canonical_fmt) {
>  		khdr.version = cpu_to_le16(khdr.version);
>  		khdr.count = cpu_to_le64(khdr.count);
>  		khdr.buffer_size = cpu_to_le64(khdr.buffer_size);
>  	}
> -	memcpy(file.buf, &khdr, sizeof(khdr));
> +	memcpy(ima_kexec_file.buf, &khdr, sizeof(khdr));
>  
>  	print_hex_dump_debug("ima dump: ", DUMP_PREFIX_NONE, 16, 1,
> -			     file.buf, file.count < 100 ? file.count : 100,
> +			     ima_kexec_file.buf, ima_kexec_file.count < 100 ?
> +			     ima_kexec_file.count : 100,
>  			     true);
>  
> -	*buffer_size = file.count;
> -	*buffer = file.buf;
> -out:
> -	if (ret == -EINVAL)
> -		vfree(file.buf);
> -	return ret;
> +	*buffer_size = ima_kexec_file.count;
> +	*buffer = ima_kexec_file.buf;
> +
> +	return 0;
>  }
>  
>  /*
> @@ -108,13 +144,20 @@ void ima_add_kexec_buffer(struct kimage *image)
>  		return;
>  	}
>  
> -	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
> -				  kexec_segment_size);
> -	if (!kexec_buffer) {
> +	ret = ima_alloc_kexec_file_buf(kexec_segment_size);
> +	if (ret < 0) {
>  		pr_err("Not enough memory for the kexec measurement buffer.\n");
>  		return;
>  	}
>  
> +	ret = ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
> +					kexec_segment_size);
> +	if (ret < 0) {
> +		pr_err("%s: Failed to dump IMA measurements. Error:%d.\n",
> +		       __func__, ret);

Please remove "__func__" from the error message.

> +		return;
> +	}
> +
>  	kbuf.buffer = kexec_buffer;
>  	kbuf.bufsz = kexec_buffer_size;
>  	kbuf.memsz = kexec_segment_size;
> @@ -129,6 +172,12 @@ void ima_add_kexec_buffer(struct kimage *image)
>  	image->ima_buffer_size = kexec_segment_size;
>  	image->ima_buffer = kexec_buffer;
>  
> +	/*
> +	 * kexec owns kexec_buffer after kexec_add_buffer() is called
> +	 * and it will vfree() that buffer.
> +	 */
> +	ima_reset_kexec_file(&ima_kexec_file);
> +
>  	kexec_dprintk("kexec measurement buffer for the loaded kernel at
> 0x%lx.\n",
>  		      kbuf.mem);
>  }

thanks,

Mimi