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

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/14/24 10:38, 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

as -> a

>     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_free_kexec_file_buf(&ima_kexec_file);
> +
> +	/* 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;
> +	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;

If you return -EINVAL then the caller should not look at the buffer but 
at 'ret' (5/8). So I don't think it's necessary to initialize these 
variables since the caller shouldn't look at them.

> +		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) {
>   			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__);
>   			break;
>   		}
>   	}
>   
> -	if (ret < 0)
> -		goto out;
> -
>   	/*
>   	 * 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);
> +		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.
> +	 */

Actually, that's not quite right what I told you.   "kexec owns 
kexec_buffer due to ima->ima_buffer and it will vfree() this buffer."


> +	ima_reset_kexec_file(&ima_kexec_file);
> +
>   	kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
>   		      kbuf.mem);
>   }

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