Re: [PATCH v10 6/8] ima: kexec: move IMA log copy from kexec load to execute

[steven chen <chenste@linux.microsoft.com>]

On 3/19/2025 1:53 PM, Mimi Zohar wrote:
> On Mon, 2025-03-17 at 18:04 -0700, steven chen wrote:
>> ima_dump_measurement_list() is called during kexec 'load', which may
>> result in loss of IMA measurements during kexec soft reboot. Due to
>> missed measurements that only occurred after kexec 'load', this function
>> needs to be called during kexec 'execute'.
> -> , defer calling ima_dump_measurement_list() to kexec 'execute'.
>
>> This patch includes the following changes:
>>   - Implement kimage_file_post_load() function to be invoked after the new
>>     kernel image has been loaded for kexec.
>>   - Call kimage_file_post_load() from kexec_file_load() syscall only for
>>     kexec soft reboot scenarios and not for KEXEC_FILE_ON_CRASH.  It will
>>     map the IMA segment, and register reboot notifier for the function
>>     ima_update_kexec_buffer() which would copy the IMA log at kexec soft
>>     reboot.
>>   - Make kexec_segment_size variable local static to the file so that it
>>     becomes accessible both during kexec 'load' and 'execute'.
>>   - Move ima_dump_measurement_list() call from ima_add_kexec_buffer()
>>     to ima_update_kexec_buffer().
>>   - Copy the measurement list as much as possible.
> Let's summarize the above changes, as below, and then remove the list.
>
> Define and call the new kimage_file_post_load() to call ima_kexec_post_load(),
> which registers the reboot notifier (ima_update_kexec_buffer).
>
> Finally, move ima_dump_measurement_list() from ima_add_kexec_buffer()
> to ima_update_kexec_buffer() to defer copying the measurement list.
>
>>   - Remove ima_reset_kexec_file() call from ima_add_kexec_buffer(), now
>>     that the buffer is being copied at kexec 'execute', and resetting the
>>     file at kexec 'load' would corrupt the buffer.
> Instead of adding and then removing the ima_reset_kexec_file() call from
> ima_add_kexec_buffer(), defer adding the test in ima_alloc_kexec_file_buf() to
> see if the segment size has changed.  That should be a subsequent patch, after
> this one.
>
> ima_reset_kexec_file() is then ever called from only one place.  Combine
> ima_reset_kexec_file() with ima_free_kexec_file_buf().
>
> thanks,
>
> Mimi

Hi Mimi,

I will update the patchset in next version.

Thanks,

Steven

>
>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> Cc: Eric Biederman <ebiederm@xmission.com>
>> Cc: Baoquan He <bhe@redhat.com>
>> Cc: Vivek Goyal <vgoyal@redhat.com>
>> Cc: Dave Young <dyoung@redhat.com>
>> Signed-off-by: steven chen <chenste@linux.microsoft.com>
>> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
>> ---
>>   kernel/kexec_file.c                | 10 ++++++
>>   security/integrity/ima/ima_kexec.c | 51 ++++++++++++++++++------------
>>   2 files changed, 40 insertions(+), 21 deletions(-)
>>
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 606132253c79..ab449b43aaee 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -201,6 +201,13 @@ kimage_validate_signature(struct kimage *image)
>>   }
>>   #endif
>>   
>> +static void kimage_file_post_load(struct kimage *image)
>> +{
>> +#ifdef CONFIG_IMA_KEXEC
>> +	ima_kexec_post_load(image);
>> +#endif
>> +}
>> +
>>   /*
>>    * In file mode list of segments is prepared by kernel. Copy relevant
>>    * data from user space, do error checking, prepare segment list
>> @@ -428,6 +435,9 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
>>   
>>   	kimage_terminate(image);
>>   
>> +	if (!(flags & KEXEC_FILE_ON_CRASH))
>> +		kimage_file_post_load(image);
>> +
>>   	ret = machine_kexec_post_load(image);
>>   	if (ret)
>>   		goto out;
>> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
>> index 9336c4f60650..c390c745f882 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -19,6 +19,7 @@
>>   #ifdef CONFIG_IMA_KEXEC
>>   static bool ima_kexec_update_registered;
>>   static struct seq_file ima_kexec_file;
>> +static size_t kexec_segment_size;
>>   static void *ima_kexec_buffer;
>>   
>>   static void ima_reset_kexec_file(struct seq_file *sf)
>> @@ -67,7 +68,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>>    *    if the size of the allocated memory is not less than the size of IMA measurement list
>>    *        copy the measurement list to the allocated memory.
>>    *    else
>> - *        return error
>> + *        copy the measurement list as much as possible.
>>    */
>>   static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>>   				     unsigned long segment_size)
>> @@ -95,9 +96,6 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>>   		}
>>   	}
>>   
>> -	if (ret < 0)
>> -		goto out;
>> -
>>   	/*
>>   	 * fill in reserved space with some buffer details
>>   	 * (eg. version, buffer size, number of measurements)
>> @@ -117,7 +115,7 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>>   
>>   	*buffer_size = ima_kexec_file.count;
>>   	*buffer = ima_kexec_file.buf;
>> -out:
>> +
>>   	return ret;
>>   }
>>   
>> @@ -135,9 +133,8 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   	unsigned long binary_runtime_size;
>>   
>>   	/* use more understandable variable names than defined in kbuf */
>> +	size_t kexec_buffer_size = 0;
>>   	void *kexec_buffer = NULL;
>> -	size_t kexec_buffer_size;
>> -	size_t kexec_segment_size;
>>   	int ret;
>>   
>>   	/*
>> @@ -162,13 +159,6 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   		return;
>>   	}
>>   
>> -	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
>> -				  kexec_segment_size);
>> -	if (!kexec_buffer) {
>> -		pr_err("Not enough memory for the kexec measurement buffer.\n");
>> -		return;
>> -	}
>> -
>>   	kbuf.buffer = kexec_buffer;
>>   	kbuf.bufsz = kexec_buffer_size;
>>   	kbuf.memsz = kexec_segment_size;
>> @@ -186,12 +176,6 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   	image->ima_segment_index = image->nr_segments - 1;
>>   	image->is_ima_segment_index_set = true;
>>   
>> -	/*
>> -	 * 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);
>>   }
>> @@ -202,7 +186,32 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   static int ima_update_kexec_buffer(struct notifier_block *self,
>>   				   unsigned long action, void *data)
>>   {
>> -	return NOTIFY_OK;
>> +	size_t buf_size = 0;
>> +	int ret = NOTIFY_OK;
>> +	void *buf = NULL;
>> +
>> +	if (!kexec_in_progress) {
>> +		pr_info("No kexec in progress.\n");
>> +		return ret;
>> +	}
>> +
>> +	if (!ima_kexec_buffer) {
>> +		pr_err("Kexec buffer not set.\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = ima_dump_measurement_list(&buf_size, &buf, kexec_segment_size);
>> +
>> +	if (ret)
>> +		pr_err("Dump measurements failed. Error:%d\n", ret);
>> +
>> +	if (buf_size != 0)
>> +		memcpy(ima_kexec_buffer, buf, buf_size);
>> +
>> +	kimage_unmap_segment(ima_kexec_buffer);
>> +	ima_kexec_buffer = NULL;
>> +
>> +	return ret;
>>   }
>>   
>>   static struct notifier_block update_buffer_nb = {