Re: [PATCH v7 3/7] ima: kexec: skip IMA segment validation after kexec soft reboot

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

On 2/4/2025 11:39 AM, Stefan Berger wrote:
> On 2/3/25 6:20 PM, steven chen wrote:
>> kexec_calculate_store_digests() calculates and stores the digest of the
>> segment at kexec_file_load syscall where the IMA segment is also
>> allocated.  With this series, the IMA segment will be updated with the
>> measurement log at kexec excute stage when soft reboot is initiated.
>
> s/excute/execute
>
>> Therefore, it may fail digest verification in verify_sha256_digest()
>> after kexec soft reboot into the new kernel. Therefore, the digest
>> calculation/verification of the IMA segment needs to be skipped.
>>
>> Skip IMA segment from calculating and storing digest in function
>
> Skip the calculation and storing of the digest of the IMA segment in 
> kexec_calculate_store_digests() so that ...
>
>
>> kexec_calculate_store_digests() so that it is not added to the
>> 'purgatory_sha_regions'.
>>
>> Since verify_sha256_digest() only verifies 'purgatory_sha_regions',
>> no change is needed in verify_sha256_digest() in this context.
>>
>> With this change, the IMA segment is not included in the digest
>> calculation, storage, and verification.
>>
>> Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> Signed-off-by: steven chen <chenste@linux.microsoft.com>
> > --->   include/linux/kexec.h              |  3 +++
>>   kernel/kexec_file.c                | 23 +++++++++++++++++++++++
>>   security/integrity/ima/ima_kexec.c |  3 +++
>>   3 files changed, 29 insertions(+)
>>
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index f8413ea5c8c8..f3246e881ac8 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -362,6 +362,9 @@ struct kimage {
>>         phys_addr_t ima_buffer_addr;
>>       size_t ima_buffer_size;
>> +
>> +    unsigned long ima_segment_index;
>> +    bool is_ima_segment_index_set;
>>   #endif
>>         /* Core ELF header buffer */
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 3eedb8c226ad..a3370a0dce20 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -38,6 +38,22 @@ void set_kexec_sig_enforced(void)
>>   }
>>   #endif
>>   +#ifdef CONFIG_IMA_KEXEC
>> +static bool check_ima_segment_index(struct kimage *image, int i)
>> +{
>> +    if (image->is_ima_segment_index_set &&
>> +            i == image->ima_segment_index)
>
> The 'i =' should be indented under 'image->'.
>
> With these nits fixed:
>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
>
>> +        return true;
>> +    else
>> +        return false;
>> +}
>> +#else
>> +static bool check_ima_segment_index(struct kimage *image, int i)
>> +{
>> +    return false;
>> +}
>> +#endif
>> +
>>   static int kexec_calculate_store_digests(struct kimage *image);
>>     /* Maximum size in bytes for kernel/initrd files. */
>> @@ -764,6 +780,13 @@ static int kexec_calculate_store_digests(struct 
>> kimage *image)
>>           if (ksegment->kbuf == pi->purgatory_buf)
>>               continue;
>>   +        /*
>> +         * Skip the segment if ima_segment_index is set and matches
>> +         * the current index
>> +         */
>> +        if (check_ima_segment_index(image, i))
>> +            continue;
>> +
>>           ret = crypto_shash_update(desc, ksegment->kbuf,
>>                         ksegment->bufsz);
>>           if (ret)
>> diff --git a/security/integrity/ima/ima_kexec.c 
>> b/security/integrity/ima/ima_kexec.c
>> index b60a902460e2..283860d20521 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -162,6 +162,7 @@ void ima_add_kexec_buffer(struct kimage *image)
>>       kbuf.buffer = kexec_buffer;
>>       kbuf.bufsz = kexec_buffer_size;
>>       kbuf.memsz = kexec_segment_size;
>> +    image->is_ima_segment_index_set = false;
>>       ret = kexec_add_buffer(&kbuf);
>>       if (ret) {
>>           pr_err("Error passing over kexec measurement buffer.\n");
>> @@ -172,6 +173,8 @@ void ima_add_kexec_buffer(struct kimage *image)
>>       image->ima_buffer_addr = kbuf.mem;
>>       image->ima_buffer_size = kexec_segment_size;
>>       image->ima_buffer = kexec_buffer;
>> +    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

Thanks, Stefan, I will update it in next version