Re: [PATCH v4 20/28] pc-bios/s390-ccw: Add signature verification for secure IPL in audit mode

[Thomas Huth <thuth@redhat.com>]

On 14/07/2025 16.54, Jared Rossi wrote:
> 
> [snip...]
>>> +
>>> +        entry++;
>>> +
>>> +        if ((uint8_t *)(&entry[1]) > tmp_sec + MAX_SECTOR_SIZE) {
>>> +            puts("Wrong entry value");
>>> +            return -EINVAL;
>>> +        }
>> Can someone who is more informed than I am of the IPL process please
>> explain to me what is the purpose of the above check?  Why does it check
>> if the next entry, the one which isn't going to be inspected/loaded, is
>> within the bounds of tmp_sec?  This has been here since this file's
>> inception and I can't find any documentation or mention that supports it.
>>
>> This code precludes any of the secure IPL changes.
>>
>> Was this actually meant to be entry[0] to ensure the actual entry we
>> want to work on is not outside the bounds of tmp_sec?  Or perhaps it was
>> meant to be done before the increment to entry?
>>
> 
> I noticed that as well and came to the same conclusions as you, which is to 
> say,
> it has always been that way and it is not clear what the purpose is, but it 
> does
> not appear to have any impact on the proposed secure IPL functionality.

I think it's meant as a check for the *end* of entry[0], so it's likely just 
a quirky way of saying:

    if (((uint8_t *)entry) + sizeof(*entry) > tmp_sec + MAX_SECTOR_SIZE)

?

  Thomas