From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5BF657FD; Fri, 7 Feb 2025 04:52:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738903953; cv=none; b=McdZMGd/6V7F0l9xWL2tS+mZY21ho3SJf1qj6PwQIHXSF/8vOFjhSD292R0/T1J6LcalXjSVRl92xPP8DxNdUecTo4FdatpW13UZlxx8haFsHAKZYKrS5qDywEdCHWIEBAQ+4U72LyOoFKsnO24EHo6kxjBWqXKXouaInCvsCuM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738903953; c=relaxed/simple; bh=DHjArMeAK3MeqFPs8ewPHAdYTmkFt/+F2+q7rMjVEsQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XE6cL20gdKOnT1Grn6e2wAAC71Ke/gq5PoTSVJkEwm0CPXBi5qyn30FuGUS8FZeBUAwz3vT7IAADe0J6yjQtD0hac0hA4oi77xJld9c+zaeWOEp3iMlBaBLUPOafrAz+QW3mBuFU3WXTDNuM8twpHgU9sNt1140ufDG+HMfaZVs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J4hOTD94; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="J4hOTD94" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1AC9C4CED1; Fri, 7 Feb 2025 04:52:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738903952; bh=DHjArMeAK3MeqFPs8ewPHAdYTmkFt/+F2+q7rMjVEsQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J4hOTD940F1xlXDm0mc5K3mDWMF8PSxayTzbGZ7yFgncZQhreabSjsW/SPkrxvWyj nSL6ezpoAY094IRO9xVo7ABLzhV1eguxz++lt/TzXCZ8K45nVXR4iXLQO5O5OvWp0K ATK9xHVbtmFdnug59ERW+h66BXmzxYNeXv29CdAsmMdv00eYEe0sd6vVofADQf05te lT0NWx4WrW5hPsI8JfAq6/8JcdwZWb3xVM2NWlDEGMKosdaJAlWafYQrvED6iGX8qh kmzhADTz8zfNueFUjkLH68uqsQf0kpB9zw+24EnTrALzamINKTukN0O7a9JCGIPQDt St5IHezNhourg== Date: Thu, 6 Feb 2025 20:52:32 -0800 From: Kees Cook To: Kevin Brodsky Cc: linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Mark Brown , Catalin Marinas , Dave Hansen , David Howells , "Eric W. Biederman" , Jann Horn , Jeff Xu , Joey Gouly , Linus Walleij , Andy Lutomirski , Marc Zyngier , Peter Zijlstra , Pierre Langlois , Quentin Perret , "Mike Rapoport (IBM)" , Ryan Roberts , Thomas Gleixner , Will Deacon , Matthew Wilcox , Qi Zheng , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [RFC PATCH 8/8] mm: Add basic tests for kpkeys_hardened_cred Message-ID: <202502062024.BCB0DED1D5@keescook> References: <20250203102809.1223255-1-kevin.brodsky@arm.com> <20250203102809.1223255-9-kevin.brodsky@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250203102809.1223255-9-kevin.brodsky@arm.com> On Mon, Feb 03, 2025 at 10:28:09AM +0000, Kevin Brodsky wrote: > Add basic tests for the kpkeys_hardened_pgtables feature: try to > perform a direct write to current->{cred,real_cred} and ensure it > fails. > > Signed-off-by: Kevin Brodsky > --- > mm/Makefile | 1 + > mm/kpkeys_hardened_cred_test.c | 42 ++++++++++++++++++++++++++++++++++ Current file naming convention[1] would be to name this as: mm/tests/kpkeys_hardened_cred_kunit.c > security/Kconfig.hardening | 11 +++++++++ > 3 files changed, 54 insertions(+) > create mode 100644 mm/kpkeys_hardened_cred_test.c > > diff --git a/mm/Makefile b/mm/Makefile > index f7263b7f45b8..2024226902d4 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -149,3 +149,4 @@ obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o > obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o > obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES) += kpkeys_hardened_pgtables.o > obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES_TEST) += kpkeys_hardened_pgtables_test.o > +obj-$(CONFIG_KPKEYS_HARDENED_CRED_TEST) += kpkeys_hardened_cred_test.o And for the Kconfig convention says[2] this should be: CONFIG_KPKEYS_HARDENED_CRED_KUNIT_TEST > diff --git a/mm/kpkeys_hardened_cred_test.c b/mm/kpkeys_hardened_cred_test.c > new file mode 100644 > index 000000000000..46048098f99d > --- /dev/null > +++ b/mm/kpkeys_hardened_cred_test.c > @@ -0,0 +1,42 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +#include > +#include > + > +static void write_cred(struct kunit *test) > +{ > + long zero = 0; > + int ret; > + > + ret = copy_to_kernel_nofault((unsigned long *)current->cred, &zero, sizeof(zero)); > + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, > + "Write to current->cred wasn't prevented"); > + > + ret = copy_to_kernel_nofault((unsigned long *)current->real_cred, &zero, sizeof(zero)); > + KUNIT_EXPECT_EQ_MSG(test, ret, -EFAULT, > + "Write to current->real_cred wasn't prevented"); This is a good negative test. I would include a positive test as well. i.e. make sure you can run copy_from_kernel_nofault() to read it successfully. Otherwise you don't know if you're just getting a bad address -- we want to distinguish between them. (This is more true for the next suggestion, since current->cred being broken would be much more obvious.) While current->cred is good and easy, I would like to see prepare_creds() exercised too to get a new cred and validate that it is equally directly readable and directly not writable, and then use the correct accessors to perform a successful write to the cred, read back the change, etc. (i.e. validate the expected behavior too.) > +} > + > +static int kpkeys_hardened_cred_suite_init(struct kunit_suite *suite) > +{ > + if (!arch_kpkeys_enabled()) { > + pr_err("Cannot run kpkeys_hardened_cred tests: kpkeys are not supported\n"); > + return 1; > + } Instead of failing ("return 1") I think this should be a "skip" (it is expected to not work if there is no support) in each test instead: if (!arch_kpkeys_enabled()) kunit_skip(test, "kpkeys are not supported\n"); I'm very happy to see tests! :) -Kees [1] https://docs.kernel.org/dev-tools/kunit/style.html#test-file-and-module-names [2] https://docs.kernel.org/dev-tools/kunit/style.html#test-kconfig-entries -- Kees Cook