[PATCH 00/35] kasan: add hardware tag-based mode for arm64
From: Andrey Konovalov
Date: Fri Aug 14 2020 - 13:27:29 EST
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 available here:
https://github.com/xairy/linux/tree/up-kasan-mte-v1
and has also been uploaded to the Linux kernel Gerrit instance:
https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/2700
This patchset is based on the v7 of the user MTE patches [3], along with
some KASAN patches cherry-picked from the current mainline.
This patchset consists of three parts:
1. Rework KASAN code to allow easier integration of the hardware tag-based
mode.
2. Introduce core in-kernel MTE routines.
3. Combine the two parts together and introduce the new mode.
For testing in QEMU hardware tag-based KASAN requires:
1. QEMU built from master [4] with these patches [5] on top.
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
[5] https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg02677.html
====== 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
>From 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 with these patches on top [3]
* 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`.
[3] https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg02677.html
====== 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
Andrey Konovalov (29):
kasan: KASAN_VMALLOC depends on KASAN_GENERIC
kasan: group vmalloc code
kasan: shadow declarations only for software modes
kasan: rename (un)poison_shadow to (un)poison_memory
kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_*
kasan: only build init.c for software modes
kasan: split out shadow.c from common.c
kasan: rename generic/tags_report.c files
kasan: don't duplicate config dependencies
kasan: hide invalid free check implementation
kasan: decode stack frame only with KASAN_STACK_ENABLE
kasan, arm64: only init shadow for software modes
kasan, arm64: only use kasan_depth for software modes
kasan: rename addr_has_shadow to addr_has_metadata
kasan: rename print_shadow_for_address to print_memory_metadata
kasan: kasan_non_canonical_hook only for software modes
kasan: rename SHADOW layout macros to META
kasan: separate metadata_fetch_row for each mode
kasan: don't allow SW_TAGS with ARM64_MTE
kasan: introduce CONFIG_KASAN_HW_TAGS
kasan, arm64: align allocations for HW_TAGS
kasan: define KASAN_GRANULE_SIZE for HW_TAGS
kasan, x86, s390: update undef CONFIG_KASAN
kasan, arm64: expand CONFIG_KASAN checks
kasan, arm64: implement HW_TAGS runtime
kasan, arm64: print report from tag fault handler
kasan, slub: reset tags when accessing metadata
kasan, arm64: enable CONFIG_KASAN_HW_TAGS
kasan: add documentation for hardware tag-based mode
Vincenzo Frascino (6):
arm64: mte: Add in-kernel MTE helpers
arm64: mte: Add in-kernel tag fault handler
arm64: mte: Enable in-kernel MTE
arm64: mte: Convert gcr_user into an exclude mask
arm64: mte: Switch GCR_EL1 in kernel entry and exit
kasan, arm64: Enable TBI EL1
Documentation/dev-tools/kasan.rst | 75 ++-
arch/arm64/Kconfig | 3 +-
arch/arm64/Makefile | 2 +-
arch/arm64/include/asm/assembler.h | 2 +-
arch/arm64/include/asm/cache.h | 3 +
arch/arm64/include/asm/esr.h | 1 +
arch/arm64/include/asm/kasan.h | 8 +-
arch/arm64/include/asm/memory.h | 6 +-
arch/arm64/include/asm/mte.h | 54 ++-
arch/arm64/include/asm/mte_asm.h | 10 +
arch/arm64/include/asm/processor.h | 2 +-
arch/arm64/include/asm/string.h | 5 +-
arch/arm64/kernel/asm-offsets.c | 3 +
arch/arm64/kernel/cpufeature.c | 11 +-
arch/arm64/kernel/entry.S | 28 ++
arch/arm64/kernel/head.S | 2 +-
arch/arm64/kernel/image-vars.h | 2 +-
arch/arm64/kernel/mte.c | 87 +++-
arch/arm64/kernel/setup.c | 1 -
arch/arm64/lib/mte.S | 41 ++
arch/arm64/mm/dump.c | 6 +-
arch/arm64/mm/fault.c | 59 ++-
arch/arm64/mm/kasan_init.c | 22 +-
arch/arm64/mm/proc.S | 2 +-
arch/s390/boot/string.c | 1 +
arch/x86/boot/compressed/misc.h | 1 +
include/linux/kasan-checks.h | 2 +-
include/linux/kasan.h | 110 +++--
include/linux/mm.h | 2 +-
include/linux/moduleloader.h | 3 +-
include/linux/page-flags-layout.h | 2 +-
include/linux/sched.h | 2 +-
include/linux/string.h | 2 +-
init/init_task.c | 2 +-
kernel/fork.c | 4 +-
lib/Kconfig.kasan | 60 ++-
lib/test_kasan.c | 2 +-
mm/kasan/Makefile | 21 +-
mm/kasan/common.c | 554 ++--------------------
mm/kasan/generic.c | 33 +-
mm/kasan/generic_report.c | 165 -------
mm/kasan/init.c | 10 +-
mm/kasan/kasan.h | 45 +-
mm/kasan/mte.c | 76 +++
mm/kasan/report.c | 254 ++--------
mm/kasan/report_generic.c | 331 +++++++++++++
mm/kasan/report_mte.c | 47 ++
mm/kasan/{tags_report.c => report_tags.c} | 7 +-
mm/kasan/shadow.c | 509 ++++++++++++++++++++
mm/kasan/tags.c | 14 +-
mm/page_poison.c | 2 +-
mm/ptdump.c | 13 +-
mm/slab_common.c | 2 +-
mm/slub.c | 25 +-
scripts/Makefile.lib | 2 +
55 files changed, 1653 insertions(+), 1085 deletions(-)
create mode 100644 arch/arm64/include/asm/mte_asm.h
delete mode 100644 mm/kasan/generic_report.c
create mode 100644 mm/kasan/mte.c
create mode 100644 mm/kasan/report_generic.c
create mode 100644 mm/kasan/report_mte.c
rename mm/kasan/{tags_report.c => report_tags.c} (94%)
create mode 100644 mm/kasan/shadow.c
--
2.28.0.220.ged08abb693-goog