On Wed, Oct 14, 2020 at 10:44 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > > This patchset is not complete (see particular TODOs in the last patch), > and I haven't performed any benchmarking yet, but I would like to start the > discussion now and hear people's opinions regarding the questions mentioned > below. > > === Overview > > This patchset adopts the existing hardware tag-based KASAN mode [1] for > use in production as a memory corruption mitigation. 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 current plan is reuse CONFIG_KASAN_HW_TAGS for production, but add a > boot time switch, that allows to choose between a debugging mode, that > includes all KASAN features as they are, and a production mode, that only > includes the essentials like tag checking. > > 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 initiative [5]. > > The last patch of this series adds a new boot time parameter called > kasan_mode, which can have the following values: > > - "kasan_mode=on" - only production features > - "kasan_mode=debug" - all debug features > - "kasan_mode=off" - no checks at all (not implemented yet) > > Currently outlined differences between "on" and "debug": > > - "on" doesn't keep track of alloc/free stacks, and therefore doesn't > require the additional memory to store those > - "on" uses asyncronous tag checking (not implemented yet) > > === Questions > > The intention with this kind of a high level switch is to hide the > implementation details. Arguably, we could add multiple switches that allow > to separately control each KASAN or MTE feature, but I'm not sure there's > much value in that. > > Does this make sense? Any preference regarding the name of the parameter > and its values? > > What should be the default when the parameter is not specified? I would > argue that it should be "debug" (for hardware that supports MTE, otherwise > "off"), as it's the implied default for all other KASAN modes. > > Should we somehow control whether to panic the kernel on a tag fault? > Another boot time parameter perhaps? > > Any ideas as to how properly estimate the slowdown? As there's no > MTE-enabled hardware yet, the only way to test these patches is use an > emulator (like QEMU). The delay that is added by the emulator (for setting > and checking the tags) is different from the hardware delay, and this skews > the results. > > A question to KASAN maintainers: what would be the best way to support the > "off" mode? I see two potential approaches: add a check into each kasan > callback (easier to implement, but we still call kasan callbacks, even > though they immediately return), or add inline header wrappers that do the > same. CC Kostya and Serban. > > === Notes > > This patchset is available here: > > https://github.com/xairy/linux/tree/up-prod-mte-rfc1 > > and on Gerrit here: > > https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/3460 > > This patchset is based on v5 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://lore.kernel.org/linux-arm-kernel/cover.1602535397.git.andreyknvl@xxxxxxxxxx/ > [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 > > Andrey Konovalov (8): > kasan: simplify quarantine_put call > kasan: rename get_alloc/free_info > kasan: introduce set_alloc_info > kasan: unpoison stack only with CONFIG_KASAN_STACK > kasan: mark kasan_init_tags as __init > kasan, arm64: move initialization message > arm64: kasan: Add system_supports_tags helper > kasan: add and integrate kasan_mode boot param > > arch/arm64/include/asm/memory.h | 1 + > arch/arm64/kernel/sleep.S | 2 +- > arch/arm64/mm/kasan_init.c | 3 ++ > arch/x86/kernel/acpi/wakeup_64.S | 2 +- > include/linux/kasan.h | 14 ++--- > mm/kasan/common.c | 90 ++++++++++++++++++-------------- > mm/kasan/generic.c | 18 ++++--- > mm/kasan/hw_tags.c | 63 ++++++++++++++++++++-- > mm/kasan/kasan.h | 25 ++++++--- > mm/kasan/quarantine.c | 5 +- > mm/kasan/report.c | 22 +++++--- > mm/kasan/report_sw_tags.c | 2 +- > mm/kasan/sw_tags.c | 14 +++-- > 13 files changed, 182 insertions(+), 79 deletions(-) > > -- > 2.28.0.1011.ga647a8990f-goog >
