Re: [PATCH ima-evm-utils v2] Add tests for MMAP_CHECK and MMAP_CHECK_REQPROT hooks

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

On Wed, 2023-02-01 at 08:48 -0500, Mimi Zohar wrote:
> On Tue, 2023-01-31 at 19:00 -0500, Mimi Zohar wrote:
> > On Tue, 2023-01-31 at 18:42 +0100, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@huawei.com>
> > > 
> > > Add tests to ensure that, after applying the kernel patch 'ima: Align
> > > ima_file_mmap() parameters with mmap_file LSM hook', the MMAP_CHECK hook
> > > checks the protections applied by the kernel and not those requested by the
> > > application.
> > > 
> > > Also ensure that after applying 'ima: Introduce MMAP_CHECK_REQPROT hook',
> > > the MMAP_CHECK_REQPROT hook checks the protections requested by the
> > > application.
> > > 
> > > Test both with the test_mmap application that by default requests the
> > > PROT_READ protection flag. Its syntax is:
> > > 
> > > test_mmap <file> <mode>
> > > 
> > > where mode can be:
> > > - exec: adds the PROT_EXEC protection flag to mmap()
> > > - read_implies_exec: calls the personality() system call with
> > >                      READ_IMPLIES_EXEC as the first argument before mmap()
> > > - mprotect: adds the PROT_EXEC protection flag to a memory area in addition
> > >             to PROT_READ
> > > - exec_on_writable: calls mmap() with PROT_EXEC on a file which has a
> > >                     writable mapping
> > > 
> > > Check the different combinations of hooks/modes and ensure that a
> > > measurement entry is found in the IMA measurement list only when it is
> > > expected. No measurement entry should be found when only the PROT_READ
> > > protection flag is requested or the matching policy rule has the
> > > MMAP_CHECK_REQPROT hook and the personality() system call was called with
> > > READ_IMPLIES_EXEC.
> > > 
> > > mprotect() with PROT_EXEC on an existing memory area protected with
> > > PROT_READ should be denied (with an appraisal rule), regardless of the MMAP
> > > hook specified in the policy. The same applies for mmap() with PROT_EXEC on
> > > a file with a writable mapping.
> > > 
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > Nice!   Including some comments, or at least the test assumption, would
> > help simplify reviewing the code.
> 
> An example of a test assumption, or background information, for the
> "mprotect" test is described in the ima_file_mprotect() function
> comment:
> 
>  * Files can be mmap'ed read/write and later changed to execute to circumvent
>  * IMA's mmap appraisal policy rules.  Due to locking issues (mmap semaphore
>  * would be taken before i_mutex), files can not be measured or appraised at
>  * this point.  Eliminate this integrity gap by denying the mprotect
>  * PROT_EXECUTE change, if an mmap appraise policy rule exists.

Ok, I added the description to each test. Will send the new patch
shortly.

Roberto