linux-kernel - Re: [PATCH v13 3/3] selftest/interpreter: Add tests for trusted

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Message-ID: <202110081543.1B6BF22@keescook>
Date:   Fri, 8 Oct 2021 15:44:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Christian Heimes <christian@...hon.org>,
        Deven Bowers <deven.desai@...ux.microsoft.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Eric Chiang <ericchiang@...gle.com>,
        Florian Weimer <fweimer@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Paul Moore <paul@...l-moore.com>,
        Philippe Trébuchet 
        <philippe.trebuchet@....gouv.fr>,
        Scott Shell <scottsh@...rosoft.com>,
        Shuah Khan <shuah@...nel.org>,
        Steve Dower <steve.dower@...hon.org>,
        Steve Grubb <sgrubb@...hat.com>,
        Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v13 3/3] selftest/interpreter: Add tests for
 trusted_for(2) policies

On Fri, Oct 08, 2021 at 12:21:12PM +0200, Mickaël Salaün wrote:
> 
> On 07/10/2021 21:48, Kees Cook wrote:
> > On Thu, Oct 07, 2021 at 08:23:20PM +0200, Mickaël Salaün wrote:
> 
> [...]
> 
> >> diff --git a/tools/testing/selftests/interpreter/Makefile b/tools/testing/selftests/interpreter/Makefile
> >> new file mode 100644
> >> index 000000000000..1f71a161d40b
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/interpreter/Makefile
> >> @@ -0,0 +1,21 @@
> >> +# SPDX-License-Identifier: GPL-2.0
> >> +
> >> +CFLAGS += -Wall -O2
> >> +LDLIBS += -lcap
> >> +
> >> +src_test := $(wildcard *_test.c)
> >> +TEST_GEN_PROGS := $(src_test:.c=)
> >> +
> >> +KSFT_KHDR_INSTALL := 1
> >> +include ../lib.mk
> >> +
> >> +khdr_dir = $(top_srcdir)/usr/include
> >> +
> >> +$(khdr_dir)/asm-generic/unistd.h: khdr
> >> +	@:
> >> +
> >> +$(khdr_dir)/linux/trusted-for.h: khdr
> >> +	@:
> >> +
> >> +$(OUTPUT)/%_test: %_test.c $(khdr_dir)/asm-generic/unistd.h $(khdr_dir)/linux/trusted-for.h ../kselftest_harness.h
> >> +	$(LINK.c) $< $(LDLIBS) -o $@ -I$(khdr_dir)
> > 
> > Is all this really needed?
> 
> Yes, all this is needed to be sure that the tests will be rebuild when a
> dependency change (either one of the header files or a source file).
> 
> > 
> > - CFLAGS and LDLIBS will be used by the default rules
> 
> Yes, but it will only run the build command when a source file change,
> not a header file.
> 
> > - khdr is already a pre-dependency when KSFT_KHDR_INSTALL is set
> 
> Yes, but it is not enough to rebuild the tests (and check the installed
> files) when a header file change.
> 
> > - kselftest_harness.h is already a build-dep (see LOCAL_HDRS)
> 
> Yes, but without an explicit requirement, changing kselftest_harness.h
> doesn't force a rebuild.
> 
> > - TEST_GEN_PROGS's .c files are already build-deps
> 
> It is not enough to trigger test rebuilds.
> 
> > 
> > kselftest does, oddly, lack a common -I when KSFT_KHDR_INSTALL is set
> > (which likely should get fixed, though separately from here).
> > 
> > I think you just want:
> > 
> > 
> > src_test := $(wildcard *_test.c)
> > TEST_GEN_PROGS := $(src_test:.c=)
> > 
> > KSFT_KHDR_INSTALL := 1
> > include ../lib.mk
> > 
> > CFLAGS += -Wall -O2 -I$(BUILD)/usr/include
> > LDLIBS += -lcap
> > 
> > $(OUTPUT)/%_test: $(BUILD)/usr/include/linux/trusted-for.h
> > 
> > 
> > (untested)
> > 
> Yep, I re-checked and my Makefile is correct. I didn't find a way to
> make it lighter while correctly handling dependencies.
> I'll just move the -I to CFLAGS.

Okay, thanks for double-checking these. I'll try to fix up kselftests to
DTRT here.

-- 
Kees Cook