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@xxxxxxx>. 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 >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 * 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@xxxxxxx> ====== History Change v10->v11: (Andrey:) - Rebase onto the latest mm. Changes v9->v10: (Andrey:) - Rebase onto the mm tree. - Drop "s390/kasan: include asm/page.h from asm/kasan.h" as linux-next already contains this fix queued up with other s390 KASAN changes. - Add kfence checks in mm/kasan/hw_tags.c. - Rename KASAN_GRANULE_PAGE to KASAN_MEMORY_PER_SHADOW_PAGE. - Clarify "slab memory" in documentation. - Add a comment to CC_HAS_WORKING_NOSANITIZE_ADDRESS. - Drop "kasan: kasan_non_canonical_hook only for software modes" as KASAN_INLINE already depends on KASAN_GENERIC || KASAN_SW_TAGS. - Mark kasan_init_hw_tags() as __init, as non-init parts have been moved to kasan_init_hw_tags_cpu(). - Rename kasan_(un)poison_memory() to (kasan_)(un)poison_range(). (Vincenzo:) - Add smb_wmb() to copy_highpage(). - Rename mte_enable() to mte_enable_kernel(). - Address review comments on selftest code. - Address concerns from checkpatch.pl (courtesy of Marco Elver). - Integrate a fixup from Marco Elver for code alignment. Changes v8->v9: (Andrey:) - Drop __init for kasan_init_hw_tags. - Split out mte_enable() from mte_init_tags(). - Fix incorrect commit author. - Revert addr_has_metadata() change done in a previous version, otherwise KASAN fails to print metadata for page_alloc allocations. - Split kasan_init_hw_tags() into kasan_init_hw_tags_cpu() that is called for each CPU in cpu_enable_mte(), and kasan_init_hw_tags() that is called for boot CPU in smp_prepare_boot_cpu(). - Move kunit_kasan_expectation struct definition under CONFIG_KASAN. (Vincenzo:) - Address Catalin's comments for "arm64: mte: Reset the page tag in page->flags". - New patch "kasan, mm: untag page address in free_reserved_area". Changes v7->v8: (Andrey:) - Rebased onto 5.10-rc2+. - Enable in-kernel MTE via kasan_init_hw_tags() instead of doing it directly from cpu_enable_mte(). This changes mte_init_tags() to both init RRND and enable in-kernel MTE in sync mode. - Put the patches back into a logical order. - Rename KASAN_SHADOW_GRANULE_SIZE to KASAN_GRANULE_SIZE in lib/test_kasan_module.c. - Rename kasan_init_tags() to kasan_init_sw_tags() and mark as __init. Changes v6->v7: (Andrey:) - Rebase onto 5.10-rc2. - Fix pgd_t not defined build warning on s390. - Mark kasan_init_depth() as static. - Don't use mte_*() functions directly in report_hw_tags.c - Add hw_ prefix to KASAN-level definitions of arch_*() tag helpers. - Add missing <sched/task_stack.h> include to report_generic.h. Changes v5->v6: (Vincenzo:) - Re-based on 5.10-rc1. - Modified the flow of the mte fault handler in order to address an issue with word at a time routines that would affect Android init process. - Dropped Reviewed-by from the involved patches. (Andrey:) - Properly use #if CONFIG_KASAN_STACK instead of #ifdef CONFIG_KASAN_STACK_ENABLE. - Expand CONFIG_KASAN checks in arch/arm64/kernel/kaslr.c and arch/arm64/kernel/module.c. - Don't select CONFIG_CONSTRUCTORS for HW_TAGS mode. - Check PageSlab() in addr_has_metadata(). Changes v4->v5: (Vincenzo:) - Reset the tag associated by the kernel to a page when this is changed by the user. - Add a kselftest to verify that GCR_EL1 is preserved during context switch. - Squashed the TBI patch. - Addressed some review comments. - Verified the series with LTP. (Andrey:) - Put core arm64 patches first as requested by Catalin. Changes v3->v4: (Vincenzo:) - Introduced mte-def.h that contains MTE definitions. - Moved __MTE_PREAMBLE in mte.h. - Clarified which API is part of mte-kasan.h. - Removed tsk argument from mte_set_kernel_gcr(). - Addressed several nitpicks pointed out during review. (Andrey:) - Move include <asm/kasan.h> in include/linux/kasan.h to avoid build failures. - Don't move "select SLUB_DEBUG if SLUB" back and forth between patches in KASAN Kconfig. - Add arm64 prefix to "kasan: don't allow SW_TAGS with ARM64_MTE" commit. - Don't add braces when defining KASAN_GRANULE_SIZE. - Make KASAN_HW_TAGS compatible with init_on_alloc/free. Changes v2->v3: (Vincenzo:) - Use ARM64_ASM_PREAMBLE for asm macros. - Rename mte-helper.h to mte-kasan.h. The new header is meant to contain only macros and prototypes directly used in KASAN. The rest is defined in mte.h. - Update mte_get_mem_tag()/mte_get_random_tag() to used directly asm volatile() macros instead of calling library functions. - Harden mte_assign_mem_tag_range() to prevent an infinite loop in case of unaligned size. - Made sure that report_tag_fault() is executed only once. - Simplify the mte code in __cpu_setup. - Remove kprobes.h from mte.c includes. - General cleanup of the code. (Andrey:) - Use READ/WRITE_ONCE when accessing reported in do_tag_recovery(). - Move .unreq mte_tcr under CONFIG_ARM64_MTE to avoid build errors when MTE is not enabled. - Improve mm/kasan/shadow.c comment header. - Clarify what is a memory granule in "kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_" commit description. - Rename (report_)tags_sw/hw.c to to (report_)sw/hw_tags.c and drop unnecessary rename commit. - Adopt 100 lines limit for some mm/kasan/ changes. - Align arguments for stack_trace_save() call in mm/slub.c. - Restore comment before kasan_init_tags(). - Remove GNU headers from all mm/kasan/ files. - Simplify check_invalid_free() implementation tag-based modes. - Drop subsequently removed report_tag_fault() implementation. - Add KASAN_GRANULE_PAGE and use instead of PAGE_SIZE * KASAN_GRANULE_SIZE. - Move kasan_enable/disable_current() declarations to simplify include/linux/kasan.h. - Drop dependency on CONFIG_SLUB_DEBUG. - Clarify the purpose of CONFIG_STACKTRACE in KASAN Kconfig. Changes v1->v2: - Rebase onto v10 of the user MTE patchset. - Only enable in-kernel MTE when KASAN_HW_TAGS is enabled. - Add a layer of arch-level indirection, so KASAN doesn't call MTE helpers directly (this will be useful in case more architectures will add support for HW_TAGS). - Don't do arm64_skip_faulting_instruction() on MTE fault, disable MTE instead. - Don't allow software tags with MTE via arch/arm64/Kconfig instead of lib/Kconfig.kasan. - Rename mm/kasan/tags.c to tags_sw.c and mte.c to tags_hw.c, and do the same for report_*.c files. - Reword HW_TAGS Kconfig help text to make it less MTE specific. - Reword and clarify Documentation. - Drop unnecessary is_el1_mte_sync_tag_check_fault(). - Change report_tag_fault() to only call kasan_report() once HW_TAGS is introduced. - Rename arch/arm64/include/asm/mte_asm.h to mte-helpers.h and move all MTE-related defines and some helper functions there. - Change mm/kasan/kasan.h to include mte-def.h instead of mte.h. - Add WARN_ON() on unaligned size to mte_set_mem_tag_range(). - Implement ldg/irg MTE routines as inline assembly. - Remove smp_wmb() from mte_set_mem_tag_range(). - Drop __must_check from mte_set_mem_tag_range() as KASAN has no use for the return value. - Drop zero size check from mte_assign_mem_tag_range(). - Drop unnecessary include <asm/kasan.h> from low-level arm64 code. - Move enabling TBI1 into __cpu_setup(). - Drop stale comment about callee-saved register from arch/arm64/kernel/entry.S. - Mark gcr_kernel_excl as __ro_after_init. - Use GENMASK() in mte_init_tags(). Andrey Konovalov (33): kasan: drop unnecessary GPL text from comment headers 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_range kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_* kasan: only build init.c for software modes kasan: split out shadow.c from common.c kasan: define KASAN_MEMORY_PER_SHADOW_PAGE kasan: rename report and tags 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, arm64: move initialization message kasan, arm64: rename kasan_init_tags and mark as __init kasan: rename addr_has_shadow to addr_has_metadata kasan: rename print_shadow_for_address to print_memory_metadata kasan: rename SHADOW layout macros to META kasan: separate metadata_fetch_row for each mode kasan, arm64: don't allow SW_TAGS with ARM64_MTE kasan: introduce CONFIG_KASAN_HW_TAGS arm64: kasan: Align allocations for HW_TAGS arm64: kasan: Add arch layer for memory tagging helpers 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, mm: reset tags when accessing metadata kasan, arm64: enable CONFIG_KASAN_HW_TAGS kasan: add documentation for hardware tag-based mode Vincenzo Frascino (9): arm64: Enable armv8.5-a asm-arch option arm64: mte: Add in-kernel MTE helpers arm64: mte: Reset the page tag in page->flags arm64: mte: Add in-kernel tag fault handler arm64: kasan: Allow enabling in-kernel MTE arm64: mte: Convert gcr_user into an exclude mask arm64: mte: Switch GCR_EL1 in kernel entry and exit kasan, mm: untag page address in free_reserved_area kselftest/arm64: Check GCR_EL1 after context switch Documentation/dev-tools/kasan.rst | 82 ++- arch/arm64/Kconfig | 9 +- arch/arm64/Makefile | 7 +- 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 | 5 +- arch/arm64/include/asm/memory.h | 15 +- arch/arm64/include/asm/mte-def.h | 14 + arch/arm64/include/asm/mte-kasan.h | 67 ++ arch/arm64/include/asm/mte.h | 22 +- arch/arm64/include/asm/processor.h | 2 +- arch/arm64/include/asm/string.h | 5 +- arch/arm64/include/asm/uaccess.h | 23 + arch/arm64/kernel/asm-offsets.c | 3 + arch/arm64/kernel/cpufeature.c | 3 + arch/arm64/kernel/entry.S | 41 ++ arch/arm64/kernel/head.S | 2 +- arch/arm64/kernel/hibernate.c | 5 + arch/arm64/kernel/image-vars.h | 2 +- arch/arm64/kernel/kaslr.c | 3 +- arch/arm64/kernel/module.c | 6 +- arch/arm64/kernel/mte.c | 118 +++- arch/arm64/kernel/setup.c | 2 +- arch/arm64/kernel/smp.c | 2 + arch/arm64/lib/mte.S | 16 + arch/arm64/mm/copypage.c | 9 + arch/arm64/mm/fault.c | 59 ++ arch/arm64/mm/kasan_init.c | 19 +- arch/arm64/mm/mteswap.c | 9 + arch/arm64/mm/proc.S | 23 +- arch/arm64/mm/ptdump.c | 6 +- arch/s390/boot/string.c | 1 + arch/x86/boot/compressed/misc.h | 1 + include/linux/kasan-checks.h | 2 +- include/linux/kasan.h | 125 ++-- 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 | 65 +- lib/test_kasan.c | 2 +- lib/test_kasan_module.c | 2 +- mm/kasan/Makefile | 25 +- mm/kasan/common.c | 577 ++---------------- mm/kasan/generic.c | 51 +- mm/kasan/generic_report.c | 165 ----- mm/kasan/hw_tags.c | 89 +++ mm/kasan/init.c | 17 +- mm/kasan/kasan.h | 74 ++- mm/kasan/quarantine.c | 10 - mm/kasan/report.c | 256 ++------ mm/kasan/report_generic.c | 327 ++++++++++ mm/kasan/report_hw_tags.c | 42 ++ mm/kasan/{tags_report.c => report_sw_tags.c} | 14 +- mm/kasan/shadow.c | 516 ++++++++++++++++ mm/kasan/{tags.c => sw_tags.c} | 24 +- mm/page_alloc.c | 9 +- mm/page_poison.c | 2 +- mm/ptdump.c | 13 +- mm/slab_common.c | 2 +- mm/slub.c | 29 +- scripts/Makefile.lib | 2 + tools/testing/selftests/arm64/mte/Makefile | 2 +- .../arm64/mte/check_gcr_el1_cswitch.c | 155 +++++ 68 files changed, 2036 insertions(+), 1165 deletions(-) create mode 100644 arch/arm64/include/asm/mte-def.h create mode 100644 arch/arm64/include/asm/mte-kasan.h delete mode 100644 mm/kasan/generic_report.c create mode 100644 mm/kasan/hw_tags.c create mode 100644 mm/kasan/report_generic.c create mode 100644 mm/kasan/report_hw_tags.c rename mm/kasan/{tags_report.c => report_sw_tags.c} (87%) create mode 100644 mm/kasan/shadow.c rename mm/kasan/{tags.c => sw_tags.c} (92%) create mode 100644 tools/testing/selftests/arm64/mte/check_gcr_el1_cswitch.c -- 2.29.2.454.gaff20da3a2-goog
