linux-kernel - Re: [PATCH ima-evm-utils v5] Add tests for MMAP_CHECK and MMAP_CHECK

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Message-ID: <6e01fda2e1f322689123955fcad4d449d036074c.camel@linux.ibm.com>
Date:   Tue, 07 Feb 2023 12:47:56 -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 v5] Add tests for MMAP_CHECK and
 MMAP_CHECK_REQPROT hooks

On Tue, 2023-02-07 at 17:57 +0100, Roberto Sassu wrote:
> On Tue, 2023-02-07 at 11:16 +0100, Roberto Sassu wrote:
> > On Mon, 2023-02-06 at 08:20 -0500, Mimi Zohar wrote:
> > > On Fri, 2023-02-03 at 13:56 +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>
> > > 
> > > Thanks, Roberto.  Other than the one comment below, it looks good.
> > > 
> > > > +
> > > > +if ! awk '$0 ~ /^(measure|appraise)/ && $0 !~ /fsuuid=/ && $0 !~ /fowner=/ { exit 1 }' < /sys/kernel/security/ima/policy; then
> > > > +	echo "${CYAN}IMA policy rules without fsuuid= and fowner=, cannot continue due to possible interference with the tests${NORM}"
> > > > +	exit "$SKIP"
> > > > +fi
> > > 
> > > The test should be limited to just MMAP_CHECK and MMAP_CHECK_REQPROT
> > > policy rules.
> > > 
> > > +if ! awk '$0 ~ /^(measure|appraise)/ && $0 ~ /func=MMAP_CHECK/ && $0 !~ /fsuuid=/ && ...
> > 
> > Oh, yes. Better.
> 
> It seems more complicated than that.
> 
> If we consider only MMAP_CHECK and MMAP_CHECK_REQPROT rules, we might
> miss rules without func= that can potentially overlap.
> 
> Overlap of measure and appraise rules per se should not be a problem,
> unless additional options are specified in the rule. In that case, the
> options of the first matching rule are taken and the other options from
> other rules might not be processed (IMA stops checking the policy when
> it has encountered rules with the possible actions, determined when the
> policy is loaded).
> 
> Also, dont_measure and dont_appraise rules are a possible concern, as
> they could be matched before ours and could change the expected
> outcome.
> 
> A proposal could be to ignore existing rules, regardless of the action,
> if they provide a different value for at least one of the policy
> keywords (in 'base' and 'lsm') present in the rule being added.
> 
> For the rules that we didn't ignore, we can accept them if they have
> the same action and no/the same policy options.

Agreed.   Since this is much more complex than the awk test, I assume
it would need to be a function.  For now keep it in the
mmap_check.test, not functions.sh.

thanks,

Mimi