Re: [PATCH v8 7/7] ima: measure kexec load and exec events as critical data

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

On 2/19/2025 8:23 AM, Stefan Berger wrote:
>
>
> On 2/18/25 5:55 PM, steven chen 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.
>>
>> The 'kexec_load' event IMA log can be found using the following command:
>> sudo cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements |
>>     grep kexec_load
>>
>> The 'kexec_load' event IMA log can be found using the following command:
>> sudo cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements |
>>     grep kexec_execute
>>
>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> Signed-off-by: steven chen <chenste@linux.microsoft.com>
>> ---
>>   security/integrity/ima/ima.h       |  6 ++++++
>>   security/integrity/ima/ima_kexec.c | 21 +++++++++++++++++++++
>>   security/integrity/ima/ima_queue.c |  5 +++++
>>   3 files changed, 32 insertions(+)
>>
>> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
>> index 4428fcf42167..1452c98242a4 100644
>> --- a/security/integrity/ima/ima.h
>> +++ b/security/integrity/ima/ima.h
>> @@ -240,6 +240,12 @@ void ima_post_key_create_or_update(struct key 
>> *keyring, struct key *key,
>>                      unsigned long flags, bool create);
>>   #endif
>>   +#ifdef CONFIG_IMA_KEXEC
>> +void ima_measure_kexec_event(const char *event_name);
>> +#else
>> +static inline void ima_measure_kexec_event(const char *event_name) {}
>> +#endif
>> +
>>   /*
>>    * The default binary_runtime_measurements list format is defined 
>> as the
>>    * platform native format.  The canonical format is defined as 
>> little-endian.
>> diff --git a/security/integrity/ima/ima_kexec.c 
>> b/security/integrity/ima/ima_kexec.c
>> index 6c8c203ad81e..8d0782e51ffa 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;
>> @@ -36,6 +38,24 @@ static void ima_free_kexec_file_buf(struct 
>> seq_file *sf)
>>       ima_reset_kexec_file(sf);
>>   }
>>   +void ima_measure_kexec_event(const char *event_name)
>> +{
>> +    char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
>> +    size_t buf_size = 0;
>> +    long len;
>> +
>> +    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);
>
> Indentation and n = scnprintf(...), as Mimi mentioned in v7.
>
>> +
>> +    ima_measure_critical_data("ima_kexec", event_name, ima_kexec_event,
>> +                  strlen(ima_kexec_event), false, NULL, 0);
>
> Replace strlen(ima_kexec_event) with 'n'.
>
> With these fixes:
>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
>
>> +}
>> +
>>   static int ima_alloc_kexec_file_buf(size_t segment_size)
>>   {
>>       /*
>> @@ -58,6 +78,7 @@ static int ima_alloc_kexec_file_buf(size_t 
>> segment_size)
>>   out:
>>       ima_kexec_file.read_pos = 0;
>>       ima_kexec_file.count = sizeof(struct ima_kexec_hdr);    /* 
>> reserved space */
>> +    ima_measure_kexec_event("kexec_load");
>>         return 0;
>>   }
>> diff --git a/security/integrity/ima/ima_queue.c 
>> b/security/integrity/ima/ima_queue.c
>> index 3dfd178d4292..6afb46989cf6 100644
>> --- a/security/integrity/ima/ima_queue.c
>> +++ b/security/integrity/ima/ima_queue.c
>> @@ -241,6 +241,11 @@ static int ima_reboot_notifier(struct 
>> notifier_block *nb,
>>                      unsigned long action,
>>                      void *data)
>>   {
>> +#ifdef CONFIG_IMA_KEXEC
>> +    if (action == SYS_RESTART && data && !strcmp(data, "kexec reboot"))
>> +        ima_measure_kexec_event("kexec_execute");
>> +#endif
>> +
>>       ima_measurements_suspend();
>>         return NOTIFY_DONE;

Hi Stefan, thanks for your comments. I will update in next version.