Re: [PATCH v7 7/7] ima: measure kexec load and exec events as critical data

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

On 2/7/2025 9:48 AM, Stefan Berger wrote:
>
>
> On 2/7/25 12:06 PM, Mimi Zohar wrote:
>> On Fri, 2025-02-07 at 10:16 -0500, Mimi Zohar wrote:
>>> On Mon, 2025-02-03 at 15:20 -0800, 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.
>>>
>>> As a reminder, please include directions for verifying the buffer 
>>> data hash against
>>> the buffer data.  The directions would be similar to those in commit 
>>> 6b4da8c0e7f
>>> ("IMA: Define a new template field buf").
>>>
>>>>
>>>> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
>>>> 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>
>>>> ---
>>>>   security/integrity/ima/ima_kexec.c | 23 +++++++++++++++++++++++
>>>>   1 file changed, 23 insertions(+)
>>>>
>>>> diff --git a/security/integrity/ima/ima_kexec.c
>>>> b/security/integrity/ima/ima_kexec.c
>>>> index c9c916f69ca7..0342ddfa9342 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);
>>>>   }
>>>>   +static 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);
>>>
>>>  From scripts/checkpatch.pl, "Alignment should match open parenthesis".
>>>
>>>> +
>>>> +    ima_measure_critical_data("ima_kexec", event_name, 
>>>> ima_kexec_event,
>>>> +                    strlen(ima_kexec_event), false, NULL,
>>>> 0);
>>>
>>>  From the kernel-doc scnprintf(), returns the number of bytes.  
>>> There should be no
>>> need to calculate it using strlen().
>>>
>>>> +}
>>>> +
>>>>   static int ima_alloc_kexec_file_buf(size_t segment_size)
>>>>   {
>>>>       /*
>>>> @@ -60,6 +80,7 @@ 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;
>>>>   }
>>>> @@ -201,6 +222,8 @@ static int ima_update_kexec_buffer(struct 
>>>> notifier_block
>>>> *self,
>>>>           return ret;
>>>>       }
>>>>   +    ima_measure_kexec_event("kexec_execute");
>>>> +
>>>>       ret = ima_dump_measurement_list(&buf_size, &buf,
>>>>                       kexec_segment_size);
>>>
>>> After fixing up and applying this patch set to 6.14.0-rc1, I'm not 
>>> seeing the
>>> "kexec_execute".  Even after changing the default extra memory, I'm 
>>> still not
>>> seeing
>>> the measurement.
>>
>> FYI, after reverting commit 254ef9541d68 ("ima: Suspend PCR extends 
>> and log appends
>> when rebooting"), I'm seeing the "kexec_execute" measurement.
>
> I would try sth. like this:
> static int ima_reboot_notifier(struct notifier_block *nb,
>                    unsigned long action,
>                    void *data)
> {
>     if (action == SYS_RESTART && data && !strcmp(data, "kexec reboot"))
>         ima_measure_kexec_event("kexec_execute");
>>
>> Mimi
>>
>>
Thanks, will fix this in 6.14.0-rc1 in next version