On Wed, Nov 4, 2020 at 4:02 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > > === Overview > > Hardware tag-based KASAN mode [1] is intended to eventually be used in > production as a security mitigation. Therefore there's a need for finer > control over KASAN features and for an existence of a kill switch. > > This patchset adds a few boot parameters for hardware tag-based KASAN that > allow to disable or otherwise control particular KASAN features. > > There's another planned patchset what will further optimize hardware > tag-based KASAN, provide proper benchmarking and tests, and will fully > enable tag-based KASAN for production use. > > Hardware tag-based KASAN relies on arm64 Memory Tagging Extension (MTE) > [2] to perform memory and pointer tagging. Please see [3] and [4] for > detailed analysis of how MTE helps to fight memory safety problems. > > The features that can be controlled are: > > 1. Whether KASAN is enabled at all. > 2. Whether KASAN collects and saves alloc/free stacks. > 3. Whether KASAN panics on a detected bug or not. > > The patch titled "kasan: add and integrate kasan boot parameters" of this > series adds a few new boot parameters. > > kasan.mode allows to choose one of three main modes: > > - kasan.mode=off - KASAN is disabled, no tag checks are performed > - kasan.mode=prod - only essential production features are enabled > - kasan.mode=full - all KASAN features are enabled > > The chosen mode provides default control values for the features mentioned > above. However it's also possible to override the default values by > providing: > > - kasan.stack=off/on - enable stacks collection > (default: on for mode=full, otherwise off) I think this was discussed before, but should this be kasan.stacktrace or something like that? In other places "kasan stack" refers to stack instrumentation, not stack trace collection. Ex.: CONFIG_KASAN_STACK > - kasan.fault=report/panic - only report tag fault or also panic > (default: report) > > If kasan.mode parameter is not provided, it defaults to full when > CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise. > > It is essential that switching between these modes doesn't require > rebuilding the kernel with different configs, as this is required by > the Android GKI (Generic Kernel Image) initiative. > > === Benchmarks > > For now I've only performed a few simple benchmarks such as measuring > kernel boot time and slab memory usage after boot. There's an upcoming > patchset which will optimize KASAN further and include more detailed > benchmarking results. > > The benchmarks were performed in QEMU and the results below exclude the > slowdown caused by QEMU memory tagging emulation (as it's different from > the slowdown that will be introduced by hardware and is therefore > irrelevant). > > KASAN_HW_TAGS=y + kasan.mode=off introduces no performance or memory > impact compared to KASAN_HW_TAGS=n. > > kasan.mode=prod (manually excluding tagging) introduces 3% of performance > and no memory impact (except memory used by hardware to store tags) > compared to kasan.mode=off. > > kasan.mode=full has about 40% performance and 30% memory impact over > kasan.mode=prod. Both come from alloc/free stack collection. > > === Notes > > This patchset is available here: > > https://github.com/xairy/linux/tree/up-boot-mte-v1 > > and on Gerrit here: > > https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/3707 > > This patchset is based on v8 of "kasan: add hardware tag-based mode for > arm64" patchset [1]. > > For testing in QEMU hardware tag-based KASAN requires: > > 1. QEMU built from master [6] (use "-machine virt,mte=on -cpu max" arguments > to run). > 2. GCC version 10. > > [1] https://lkml.org/lkml/2020/11/4/1208 > [2] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/enhancing-memory-safety > [3] https://arxiv.org/pdf/1802.09517.pdf > [4] https://github.com/microsoft/MSRC-Security-Research/blob/master/papers/2020/Security%20analysis%20of%20memory%20tagging.pdf > [5] https://source.android.com/devices/architecture/kernel/generic-kernel-image > [6] https://github.com/qemu/qemu > > === History > > Changes RFC v2 -> v1: > - Rebrand the patchset from fully enabling production use to partially > addressing that; another optimization and testing patchset will be > required. > - Rebase onto v8 of KASAN_HW_TAGS series. > - Fix "ASYNC" -> "async" typo. > - Rework depends condition for VMAP_STACK and update config text. > - Remove unneeded reset_tag() macro, use kasan_reset_tag() instead. > - Rename kasan.stack to kasan.stacks to avoid confusion with stack > instrumentation. > - Introduce kasan_stack_collection_enabled() and kasan_is_enabled() > helpers. > - Simplify kasan_stack_collection_enabled() usage. > - Rework SLAB_KASAN flag and metadata allocation (see the corresponding > patch for details). > - Allow cache merging with KASAN_HW_TAGS when kasan.stacks is off. > - Use sync mode dy default for both prod and full KASAN modes. > - Drop kasan.trap=sync/async boot parameter, as async mode isn't supported > yet. > - Choose prod or full mode depending on CONFIG_DEBUG_KERNEL when no > kasan.mode boot parameter is provided. > - Drop krealloc optimization changes, those will be included in a separate > patchset. > - Update KASAN documentation to mention boot parameters. > > Changes RFC v1 -> RFC v2: > - Rework boot parameters. > - Drop __init from empty kasan_init_tags() definition. > - Add cpu_supports_mte() helper that can be used during early boot and use > it in kasan_init_tags() > - Lots of new KASAN optimization commits. > > Andrey Konovalov (20): > kasan: simplify quarantine_put call site > kasan: rename get_alloc/free_info > kasan: introduce set_alloc_info > kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK > kasan: allow VMAP_STACK for HW_TAGS mode > kasan: remove __kasan_unpoison_stack > kasan: inline kasan_reset_tag for tag-based modes > kasan: inline random_tag for HW_TAGS > kasan: inline kasan_poison_memory and check_invalid_free > kasan: inline and rename kasan_unpoison_memory > kasan: add and integrate kasan boot parameters > kasan, mm: check kasan_enabled in annotations > kasan: simplify kasan_poison_kfree > kasan, mm: rename kasan_poison_kfree > kasan: don't round_up too much > kasan: simplify assign_tag and set_tag calls > kasan: clarify comment in __kasan_kfree_large > kasan: clean up metadata allocation and usage > kasan, mm: allow cache merging with no metadata > kasan: update documentation > > Documentation/dev-tools/kasan.rst | 180 ++++++++++++-------- > arch/Kconfig | 8 +- > arch/arm64/kernel/sleep.S | 2 +- > arch/x86/kernel/acpi/wakeup_64.S | 2 +- > include/linux/kasan.h | 253 +++++++++++++++++++++------ > include/linux/mm.h | 22 ++- > kernel/fork.c | 2 +- > mm/kasan/common.c | 274 ++++++++++++++++++------------ > mm/kasan/generic.c | 27 +-- > mm/kasan/hw_tags.c | 171 ++++++++++++++++--- > mm/kasan/kasan.h | 113 ++++++++---- > mm/kasan/quarantine.c | 13 +- > mm/kasan/report.c | 61 ++++--- > mm/kasan/report_hw_tags.c | 2 +- > mm/kasan/report_sw_tags.c | 13 +- > mm/kasan/shadow.c | 5 +- > mm/kasan/sw_tags.c | 17 +- > mm/mempool.c | 2 +- > mm/slab_common.c | 13 +- > 19 files changed, 816 insertions(+), 364 deletions(-) > > -- > 2.29.1.341.ge80a0c044ae-goog >
