Re: [PATCH v12 2/9] ima: define and call ima_alloc_kexec_file_buf()

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

On 4/17/2025 9:33 PM, Baoquan He wrote:
> Hi Steven,
>
> On 04/15/25 at 07:10pm, steven chen wrote:
>> From: Steven Chen <chenste@linux.microsoft.com>
>>
>> In the current implementation, the ima_dump_measurement_list() API is
>> called during the kexec "load" phase, where a buffer is allocated and
>> the measurement records are copied. Due to this, new events added after
>> kexec load but before kexec execute are not carried over to the new kernel
>> during kexec operation
>>
>> 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'.
> Seems you didn't add note in this patch log to mention that the IMA
> measurement list fails to verify when doing two consecuritv "kexec -s -l"
> with/without a "kexec -s -u" in between. When people do bisecting and
> come to this patch, she/he will see the failure even though it's not a
> fatal blocker.
>
> ====
> After moving the vfree() here at this stage in the patch set, the IMA
> measurement list fails to verify when doing two consecutive "kexec -s -l"
> with/without a "kexec -s -u" in between.  Only after "ima: kexec: move IMA log
> copy from kexec load to execute" the IMA measurement list verifies properly with
> the vfree() here.
> ====
>
Hi Baoquan,

Thanks for your comments. I will add this in next version.

Steven

>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
>> ---
>>   security/integrity/ima/ima_kexec.c | 46 +++++++++++++++++++++++-------
>>   1 file changed, 35 insertions(+), 11 deletions(-)
>>
>> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
>> index 650beb74346c..b12ac3619b8f 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -15,26 +15,46 @@
>>   #include "ima.h"
>>   
>>   #ifdef CONFIG_IMA_KEXEC
>> +static struct seq_file ima_kexec_file;
>> +
>> +static void ima_free_kexec_file_buf(struct seq_file *sf)
>> +{
>> +	vfree(sf->buf);
>> +	sf->buf = NULL;
>> +	sf->size = 0;
>> +	sf->read_pos = 0;
>> +	sf->count = 0;
>> +}
>> +
>> +static int ima_alloc_kexec_file_buf(size_t segment_size)
>> +{
>> +	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 seq_file ima_kexec_file;
>>   	struct ima_queue_entry *qe;
>>   	struct ima_kexec_hdr khdr;
>>   	int ret = 0;
>>   
>>   	/* segment size can't change between kexec load and execute */
>> -	ima_kexec_file.buf = vmalloc(segment_size);
>>   	if (!ima_kexec_file.buf) {
>> -		ret = -ENOMEM;
>> -		goto out;
>> +		pr_err("Kexec file buf not allocated\n");
>> +		return -EINVAL;
>>   	}
>>   
>> -	ima_kexec_file.file = NULL;
>> -	ima_kexec_file.size = segment_size;
>> -	ima_kexec_file.read_pos = 0;
>> -	ima_kexec_file.count = sizeof(khdr);	/* reserved space */
>> -
>>   	memset(&khdr, 0, sizeof(khdr));
>>   	khdr.version = 1;
>>   	/* This is an append-only list, no need to hold the RCU read lock */
>> @@ -71,8 +91,6 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>>   	*buffer_size = ima_kexec_file.count;
>>   	*buffer = ima_kexec_file.buf;
>>   out:
>> -	if (ret == -EINVAL)
>> -		vfree(ima_kexec_file.buf);
>>   	return ret;
>>   }
>>   
>> @@ -111,6 +129,12 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   		return;
>>   	}
>>   
>> +	ret = ima_alloc_kexec_file_buf(kexec_segment_size);
>> +	if (ret < 0) {
>> +		pr_err("Not enough memory for the kexec measurement buffer.\n");
>> +		return;
>> +	}
>> +
>>   	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
>>   				  kexec_segment_size);
>>   	if (!kexec_buffer) {
>> -- 
>> 2.43.0
>>