Re: [PATCH v5 8/8] ima: measure kexec load and exec events as critical data

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

On 2/14/24 10:38, Tushar Sugandhi wrote:
> The amount of memory allocated at kexec load, even with the extra memory
> allocated, might not be large enough for the entire measurement list.  The
> indeterminate interval between kexec 'load' and 'execute' could exacerbate
> this problem.
> 
> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be
> measured as critical data at kexec 'load' and 'execute' respectively.
> Report the allocated kexec segment size, IMA binary log size and the
> runtime measurements count as part of those events.
> 
> These events, and the values reported through them, serve as markers in
> the IMA log to verify the IMA events are captured during kexec soft
> reboot.  The presence of a 'kexec_load' event in between the last two
> 'boot_aggregate' events in the IMA log implies this is a kexec soft
> reboot, and not a cold-boot.  And the absence of 'kexec_execute' event
> after kexec soft reboot implies missing events in that window which
> results in inconsistency with TPM PCR quotes, necessitating a cold boot
> for a successful remote attestation.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> ---
>   security/integrity/ima/ima_kexec.c | 34 +++++++++++++++++++++++++++++-
>   1 file changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 50903d4ce880..31495a043959 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -17,6 +17,8 @@
>   #include "ima.h"
>   
>   #ifdef CONFIG_IMA_KEXEC
> +#define IMA_KEXEC_EVENT_LEN 256
> +
>   static struct seq_file ima_kexec_file;
>   static void *ima_kexec_buffer;
>   static size_t kexec_segment_size;
> @@ -38,6 +40,10 @@ static void ima_free_kexec_file_buf(struct seq_file *sf)
>   
>   static int ima_alloc_kexec_file_buf(size_t segment_size)
>   {
> +	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
> +	size_t buf_size;
> +	long len;
> +
>   	/*
>   	 * kexec 'load' may be called multiple times.
>   	 * Free and realloc the buffer only if the segment_size is
> @@ -47,7 +53,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>   	    ima_kexec_file.size == segment_size &&
>   	    ima_kexec_file.read_pos == 0 &&
>   	    ima_kexec_file.count == sizeof(struct ima_kexec_hdr))
> -		return 0;
> +		goto out;
>   
>   	ima_free_kexec_file_buf(&ima_kexec_file);
>   
> @@ -60,6 +66,18 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>   	ima_kexec_file.read_pos = 0;
>   	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
>   
> +out:
> +	buf_size = ima_get_binary_runtime_size();
> +	len = atomic_long_read(&ima_htable.len);
> +
> +	scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> +		  "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
> +		  "ima_runtime_measurements_count=%ld;",
> +		  segment_size, buf_size, len);
> +
> +	ima_measure_critical_data("ima_kexec", "kexec_load", ima_kexec_event,
> +				  strlen(ima_kexec_event), false, NULL, 0);
> +
>   	return 0;
>   }
>   
> @@ -186,10 +204,12 @@ void ima_add_kexec_buffer(struct kimage *image)
>   static int ima_update_kexec_buffer(struct notifier_block *self,
>   				   unsigned long action, void *data)
>   {
> +	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
>   	void *buf = NULL;
>   	size_t buf_size;
>   	int ret = NOTIFY_OK;
>   	bool resume = false;
> +	long len;
>   
>   	if (!kexec_in_progress) {
>   		pr_info("%s: No kexec in progress.\n", __func__);
> @@ -201,6 +221,18 @@ static int ima_update_kexec_buffer(struct notifier_block *self,
>   		return ret;
>   	}
>   
> +	buf_size = ima_get_binary_runtime_size();
> +	len = atomic_long_read(&ima_htable.len);
> +
> +	scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> +		  "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
> +		  "ima_runtime_measurements_count=%ld;",
> +		  kexec_segment_size, buf_size, len);
> +
> +	ima_measure_critical_data("ima_kexec", "kexec_execute",
> +				  ima_kexec_event, strlen(ima_kexec_event),
> +				  false, NULL, 0);
> +
>   	ima_measurements_suspend();
>   
>   	ret = ima_dump_measurement_list(&buf_size, &buf,

It's twice the same code almost in the same file. You could move it into 
a function.