linux-kernel - Re: [PATCH v18 15/15] selftests, arm64: add a selftest for passing tagged pointers to kernel

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Message-ID: <201906240802.29EB80F@keescook>
Date:   Mon, 24 Jun 2019 08:02:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-media@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v18 15/15] selftests, arm64: add a selftest for passing
 tagged pointers to kernel

On Mon, Jun 24, 2019 at 04:33:00PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends kernel ABI to allow to pass
> tagged user pointers (with the top byte set to something else other than
> 0x00) as syscall arguments.
> 
> This patch adds a simple test, that calls the uname syscall with a
> tagged user pointer as an argument. Without the kernel accepting tagged
> user pointers the test fails with EFAULT.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  tools/testing/selftests/arm64/.gitignore      |  1 +
>  tools/testing/selftests/arm64/Makefile        | 11 +++++++
>  .../testing/selftests/arm64/run_tags_test.sh  | 12 ++++++++
>  tools/testing/selftests/arm64/tags_test.c     | 29 +++++++++++++++++++
>  4 files changed, 53 insertions(+)
>  create mode 100644 tools/testing/selftests/arm64/.gitignore
>  create mode 100644 tools/testing/selftests/arm64/Makefile
>  create mode 100755 tools/testing/selftests/arm64/run_tags_test.sh
>  create mode 100644 tools/testing/selftests/arm64/tags_test.c
> 
> diff --git a/tools/testing/selftests/arm64/.gitignore b/tools/testing/selftests/arm64/.gitignore
> new file mode 100644
> index 000000000000..e8fae8d61ed6
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/.gitignore
> @@ -0,0 +1 @@
> +tags_test
> diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile
> new file mode 100644
> index 000000000000..a61b2e743e99
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/Makefile
> @@ -0,0 +1,11 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +# ARCH can be overridden by the user for cross compiling
> +ARCH ?= $(shell uname -m 2>/dev/null || echo not)
> +
> +ifneq (,$(filter $(ARCH),aarch64 arm64))
> +TEST_GEN_PROGS := tags_test
> +TEST_PROGS := run_tags_test.sh
> +endif
> +
> +include ../lib.mk
> diff --git a/tools/testing/selftests/arm64/run_tags_test.sh b/tools/testing/selftests/arm64/run_tags_test.sh
> new file mode 100755
> index 000000000000..745f11379930
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/run_tags_test.sh
> @@ -0,0 +1,12 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +
> +echo "--------------------"
> +echo "running tags test"
> +echo "--------------------"
> +./tags_test
> +if [ $? -ne 0 ]; then
> +	echo "[FAIL]"
> +else
> +	echo "[PASS]"
> +fi
> diff --git a/tools/testing/selftests/arm64/tags_test.c b/tools/testing/selftests/arm64/tags_test.c
> new file mode 100644
> index 000000000000..22a1b266e373
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/tags_test.c
> @@ -0,0 +1,29 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <stdint.h>
> +#include <sys/prctl.h>
> +#include <sys/utsname.h>
> +
> +#define SHIFT_TAG(tag)		((uint64_t)(tag) << 56)
> +#define SET_TAG(ptr, tag)	(((uint64_t)(ptr) & ~SHIFT_TAG(0xff)) | \
> +					SHIFT_TAG(tag))
> +
> +int main(void)
> +{
> +	static int tbi_enabled = 0;
> +	struct utsname *ptr, *tagged_ptr;
> +	int err;
> +
> +	if (prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE, 0, 0, 0) == 0)
> +		tbi_enabled = 1;
> +	ptr = (struct utsname *)malloc(sizeof(*ptr));
> +	if (tbi_enabled)
> +		tagged_ptr = (struct utsname *)SET_TAG(ptr, 0x42);
> +	err = uname(tagged_ptr);
> +	free(ptr);
> +
> +	return err;
> +}
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook