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authorAndrey Konovalov <andreyknvl@google.com>2020-12-22 12:00:07 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-12-22 12:55:06 -0800
commit11f094e312ae834531672aee711079c00ca39ff8 (patch)
tree13fa0286decaa5304eff791f5a82b6d10210229a /mm
parent8653b778e454a7708847aeafe689bce07aeeb94e (diff)
kasan: drop unnecessary GPL text from comment headers
Patch series "kasan: add hardware tag-based mode for arm64", v11. This patchset adds a new hardware tag-based mode to KASAN [1]. The new mode is similar to the existing software tag-based KASAN, but relies on arm64 Memory Tagging Extension (MTE) [2] to perform memory and pointer tagging (instead of shadow memory and compiler instrumentation). This patchset is co-developed and tested by Vincenzo Frascino <vincenzo.frascino@arm.com>. This patchset is available here: https://github.com/xairy/linux/tree/up-kasan-mte-v11 For testing in QEMU hardware tag-based KASAN requires: 1. QEMU built from master [4] (use "-machine virt,mte=on -cpu max" arguments to run). 2. GCC version 10. [1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html [2] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/enhancing-memory-safety [3] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux for-next/mte [4] https://github.com/qemu/qemu ====== Overview The underlying ideas of the approach used by hardware tag-based KASAN are: 1. By relying on the Top Byte Ignore (TBI) arm64 CPU feature, pointer tags are stored in the top byte of each kernel pointer. 2. With the Memory Tagging Extension (MTE) arm64 CPU feature, memory tags for kernel memory allocations are stored in a dedicated memory not accessible via normal instuctions. 3. On each memory allocation, a random tag is generated, embedded it into the returned pointer, and the corresponding memory is tagged with the same tag value. 4. With MTE the CPU performs a check on each memory access to make sure that the pointer tag matches the memory tag. 5. On a tag mismatch the CPU generates a tag fault, and a KASAN report is printed. Same as other KASAN modes, hardware tag-based KASAN is intended as a debugging feature at this point. ====== Rationale There are two main reasons for this new hardware tag-based mode: 1. Previously implemented software tag-based KASAN is being successfully used on dogfood testing devices due to its low memory overhead (as initially planned). The new hardware mode keeps the same low memory overhead, and is expected to have significantly lower performance impact, due to the tag checks being performed by the hardware. Therefore the new mode can be used as a better alternative in dogfood testing for hardware that supports MTE. 2. The new mode lays the groundwork for the planned in-kernel MTE-based memory corruption mitigation to be used in production. ====== Technical details Considering the implementation perspective, hardware tag-based KASAN is almost identical to the software mode. The key difference is using MTE for assigning and checking tags. Compared to the software mode, the hardware mode uses 4 bits per tag, as dictated by MTE. Pointer tags are stored in bits [56:60), the top 4 bits have the normal value 0xF. Having less distict tags increases the probablity of false negatives (from ~1/256 to ~1/16) in certain cases. Only synchronous exceptions are set up and used by hardware tag-based KASAN. ====== Benchmarks Note: all measurements have been performed with software emulation of Memory Tagging Extension, performance numbers for hardware tag-based KASAN on the actual hardware are expected to be better. Boot time [1]: * 2.8 sec for clean kernel * 5.7 sec for hardware tag-based KASAN * 11.8 sec for software tag-based KASAN * 11.6 sec for generic KASAN Slab memory usage after boot [2]: * 7.0 kb for clean kernel * 9.7 kb for hardware tag-based KASAN * 9.7 kb for software tag-based KASAN * 41.3 kb for generic KASAN Measurements have been performed with: * defconfig-based configs * Manually built QEMU master * QEMU arguments: -machine virt,mte=on -cpu max * CONFIG_KASAN_STACK_ENABLE disabled * CONFIG_KASAN_INLINE enabled * clang-10 as the compiler and gcc-10 as the assembler [1] Time before the ext4 driver is initialized. [2] Measured as `cat /proc/meminfo | grep Slab`. ====== Notes The cover letter for software tag-based KASAN patchset can be found here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0116523cfffa62aeb5aa3b85ce7419f3dae0c1b8 ===== Tags Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> This patch (of 41): Don't mention "GNU General Public License version 2" text explicitly, as it's already covered by the SPDX-License-Identifier. Link: https://lkml.kernel.org/r/cover.1606161801.git.andreyknvl@google.com Link: https://lkml.kernel.org/r/6ea9f5f4aa9dbbffa0d0c0a780b37699a4531034.1606161801.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Reviewed-by: Marco Elver <elver@google.com> Reviewed-by: Alexander Potapenko <glider@google.com> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Branislav Rankov <Branislav.Rankov@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/kasan/common.c5
-rw-r--r--mm/kasan/generic.c5
-rw-r--r--mm/kasan/generic_report.c5
-rw-r--r--mm/kasan/init.c5
-rw-r--r--mm/kasan/quarantine.c10
-rw-r--r--mm/kasan/report.c5
-rw-r--r--mm/kasan/tags.c5
-rw-r--r--mm/kasan/tags_report.c5
8 files changed, 0 insertions, 45 deletions
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 950fd372a07e..33d863f55db1 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -7,11 +7,6 @@
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#include <linux/export.h>
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 30c0a5038b5c..d341859a1b95 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -7,11 +7,6 @@
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index a38c7a9e192a..6bb3f66992df 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -7,11 +7,6 @@
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#include <linux/bitops.h>
diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index fe6be0be1f76..9ce8cc5b8621 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -4,11 +4,6 @@
*
* Copyright (c) 2015 Samsung Electronics Co., Ltd.
* Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#include <linux/memblock.h>
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 0e3f8494628f..693b05e2c2aa 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -6,16 +6,6 @@
* Copyright (C) 2016 Google, Inc.
*
* Based on code by Dmitry Chernenkov.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * version 2 as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * General Public License for more details.
- *
*/
#include <linux/gfp.h>
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 5a0102f37171..0a2c72ddcdeb 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -7,11 +7,6 @@
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#include <linux/bitops.h>
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index e02a36a51f42..5c8b08a25715 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -4,11 +4,6 @@
*
* Copyright (c) 2018 Google, Inc.
* Author: Andrey Konovalov <andreyknvl@google.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index bee43717d6f0..5f183501b871 100644
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -7,11 +7,6 @@
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
*/
#include <linux/bitops.h>