Re: [RFC] Persist ima logs to disk

[Raphael Gianotti <raphgi@linux.microsoft.com>]

On 1/7/2021 7:45 AM, Janne Karhunen wrote:
> On Tue, Jan 5, 2021 at 9:57 PM Raphael Gianotti
> <raphgi@linux.microsoft.com> wrote:
>
>> In a thread with Janne Karhunen[2], it was mentioned that another
>> approach, using mm had been considered. Upon some investigation the
>> approach used in this RFC still seemed adequate for solving this
>> problem.
> Curious to hear in more detail where did this land?
>
> Not sure I remember this correctly anymore, but wouldn't it be
> possible to have mmap'd tmpfile at address __heap of size __heap_sz
> and have something this simple pulling memory from it?
>
> uint8_t *get_static_buffer(size_t size)
> {
>          static size_t buf_index;
>          uint8_t *bufp = NULL;
>
>          size = ROUND_UP(size, sizeof(double));
>          if ((buf_index + size) >= __heap_sz)
>                  return NULL;
>
>          bufp = (uint8_t *)__heap + buf_index;
>          buf_index += size;
>          *bufp = 0;
>
>          return bufp;
> }
>
> Then just replace every related measurement list allocation with this
> get_static_buffer and that would be pretty much all there is to it?
>
> The mm code should automatically push those pages out when it needs
> memory. It will also read those pages back in when someone scans
> through the measurement list creating a nicely formatted one. I think.
>
>
> --
> Janne
As I replied to the other comment from Mimi, I think I may have been 
overcomplicating
it. My knowledge of mm is still not very deep, so I may have overthought 
some parts of
it and thought anything I was coming up with didn't seem like a good way 
to do it. I will
revisit this, especially since I wasn't aware of the PCR concerns Mimi 
had, which make
sense and will probably be hard to solve with the code I just sent.

Raph