linux-kernel - Re: [PATCH ima-evm-utils v2] Add tests for MMAP_CHECK and MMAP_CHECK

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Date:   Wed, 01 Feb 2023 08:48:21 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, stefanb@...ux.ibm.com,
        viro@...iv.linux.org.uk, pvorel@...e.cz,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH ima-evm-utils v2] Add tests for MMAP_CHECK and
 MMAP_CHECK_REQPROT hooks

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@...wei.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@...wei.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.

-- 
thanks,

Mimi