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@xxxxxxxxxxxxx>
> Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> ---
> 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
