Re: [PATCH v9 1/7] ima: copy only complete measurement records across kexec

[steven chen]

On 3/11/2025 5:44 AM, Mimi Zohar wrote:
> On Thu, 2025-03-06 at 21:51 -0500, Mimi Zohar wrote:
> > On Thu, 2025-03-06 at 14:45 -0800, steven chen wrote:
> > > On 3/5/2025 4:27 AM, Mimi Zohar wrote:
> > > > On Wed, 2025-03-05 at 20:08 +0800, Baoquan He wrote:
> > > > > On 03/04/25 at 11:03am, steven chen wrote:
> > > > > > Carrying the IMA measurement list across kexec requires allocating a
> > > > > > buffer and copying the measurement records.  Separate allocating the
> > > > > > buffer and copying the measurement records into separate functions in
> > > > > > order to allocate the buffer at kexec 'load' and copy the measurements
> > > > > > at kexec 'execute'.
> > > > > >
> > > > > > This patch includes the following changes:
> > > > > I don't know why one patch need include so many changes. From below log,
> > > > > it should be split into separate patches. It may not need to make one
> > > > > patch to reflect one change, we should at least split and wrap several
> > > > > kind of changes to ease patch understanding and reviewing. My personal
> > > > > opinion.
> > > > Agreed, well explained.
> > > >
> > > > Mimi
> > > >
> > > > > >    - Refactor ima_dump_measurement_list() to move the memory allocation
> > > > > >      to a separate function ima_alloc_kexec_file_buf() which allocates
> > > > > >      buffer of size 'kexec_segment_size' at kexec 'load'.
> > > > > >    - Make the local variable ima_kexec_file in ima_dump_measurement_list()
> > > > > >      a local static to the file, so that it can be accessed from
> > > > > >      ima_alloc_kexec_file_buf(). Compare actual memory required to ensure
> > > > > >      there is enough memory for the entire measurement record.
> > > > > >    - Copy only complete measurement records.
> > > > > >    - Make necessary changes to the function ima_add_kexec_buffer() to call
> > > > > >      the above two functions.
> > > > > >    - Compared the memory size allocated with memory size of the entire
> > > > > >      measurement record. Copy only complete measurement records if there
> > > > > >      is enough memory. If there is not enough memory, it will not copy
> > > > > >      any IMA measurement records, and this situation will result in a
> > > > > >      failure of remote attestation.
> > > > > >
> > > > > > Suggested-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > > > > > Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> > > > > > Signed-off-by: steven chen <chenste@xxxxxxxxxxxxxxxxxxx>
> > > I will split this patch into the following two patches:
> > >
> > >       ima: define and call ima_alloc_kexec_file_buf
> > >       ima: copy measurement records as much as possible across kexec
> > Steven, breaking up code into patches is in order to simplify patch review.
> > This is done by limiting each patch to a single "logical change" [1].  For
> > example, the change below has nothing to do with "separate allocating the buffer
> > and copying the measurement records into separate functions".
> >
> >          /* This is an append-only list, no need to hold the RCU read lock */
> >          list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
> > -               if (file.count < file.size) {
> > +               entry_size += ima_get_binary_runtime_entry_size(qe->entry);
> > +               if (entry_size <= segment_size) {
> >                          khdr.count++;
> > -                       ima_measurements_show(&file, qe);
> > +                       ima_measurements_show(&ima_kexec_file, qe);
> >                  } else {
> >                          ret = -EINVAL;
> > +                       pr_err("IMA log file is too big for Kexec buf\n");
> >                          break;
> >                  }
> >          }
> >
> > The original code potentially copied a partial last measurement record, not a
> > complete measurement record.  For ease of review, the above change is fine, but
> > it needs to be a separate patch.
> >
> > Patches:
> > 1. ima: copy only complete measurement records across kexec
> > 2. ima: define and call ima_alloc_kexec_file_buf()
> Steven,
>
> The alternative would be to revert using ima_get_binary_runtime_entry_size() and
> simply use "ima_kexec_file.count < ima_kexec_file.size".  Only
> ima_kexec_file.size would be initialized in ima_alloc_kexec_buf().  The rest
> would remain in ima_dump_measurement_list().  get_binary_runtime_size() wouldn't
> need to be made global.
>
> To further simplify the patch review, first define a separate patch to just
> rename the seq_file "file" to "ima_kexec_file".
>
> Mimi

Hi Mimi,

I will work on it.

Thanks,

Steven