Richard Henderson <richard.hender...@linaro.org> writes:
> We were incorrectly assuming that only the first byte of an MTE access > is checked against the tags. But per the ARM, unaligned accesses are > pre-decomposed into single-byte accesses. So by the time we reach the > actual MTE check in the ARM pseudocode, all accesses are aligned. > > Therefore, the first failure is always either the first byte of the > access, or the first byte of the granule. > > In addition, some of the arithmetic is off for last-first -> count. > This does not become directly visible until a later patch that passes > single bytes into this function, so ptr == ptr_last. > > Buglink: https://bugs.launchpad.net/bugs/1921948 Minor note: you can Cc: Bug 1921948 <1921...@bugs.launchpad.net> to automatically copy patches to the appropriate bugs which is useful if you don't have the Cc for the reporter. Anyway I'm trying to get the kasas unit tests running as a way of testing this (and maybe expanding with a version of Andrey's test). I suspect this may be a PEBCAC issue but I built an MTE enabled kernel with: CONFIG_HAVE_ARCH_KASAN=y CONFIG_HAVE_ARCH_KASAN_SW_TAGS=y CONFIG_HAVE_ARCH_KASAN_HW_TAGS=y CONFIG_CC_HAS_KASAN_GENERIC=y CONFIG_KASAN=y # CONFIG_KASAN_GENERIC is not set CONFIG_KASAN_HW_TAGS=y CONFIG_KASAN_STACK=1 CONFIG_KASAN_KUNIT_TEST=m CONFIG_TEST_KASAN_MODULE=m and was able to boot it. But when I insmod the kasan tests: insmod test_kasan.ko it looks like it just keeps looping failing on the same test: Ignoring spurious kernel translation fault at virtual address dead00000000010a WARNING: CPU: 0 PID: 1444 at arch/arm64/mm/fault.c:364 __do_kernel_fault+0xc4/0x1bc Modules linked in: test_kasan(+) CPU: 0 PID: 1444 Comm: kunit_try_catch Tainted: G B W 5.11.0-ajb-kasan #3 Hardware name: linux,dummy-virt (DT) pstate: 60400009 (nZCv daif +PAN -UAO -TCO BTYPE=--) pc : __do_kernel_fault+0xc4/0x1bc lr : __do_kernel_fault+0xc4/0x1bc sp : ffffffc01191b900 x29: ffffffc01191b900 x28: fcffff8001f7a880 x27: fcffff8001c01e00 x26: 0000000000000000 x25: 0000000000000001 x24: 00000000000000f4 x23: 0000000020400009 x22: dead00000000010a x21: 0000000000000025 x20: ffffffc01191b9d0 x19: 0000000097c08004 x18: 0000000000000000 x17: 000000000000000a x16: 000017a83fb75794 x15: 0000000000000030 x14: 6c656e72656b2073 x13: ffffffc010e21be0 x12: 00000000000001aa x11: 000000000000008e x10: ffffffc010e2d930 x9 : 000000000003a6d0 x8 : ffffffc010e21be0 x7 : ffffffc010e2cbe0 x6 : 0000000000000d50 x5 : ffffff8007f9c850 x4 : ffffffc01191b700 x3 : 0000000000000001 x2 : 0000000000000000 x1 : 0000000000000000 x0 : fcffff8001f7a880 Call trace: __do_kernel_fault+0xc4/0x1bc do_translation_fault+0x98/0xb0 do_mem_abort+0x44/0xb0 el1_abort+0x40/0x6c el1_sync_handler+0x6c/0xb0 el1_sync+0x70/0x100 kasan_update_kunit_status+0x6c/0x1ac kasan_report_invalid_free+0x34/0xa0 ____kasan_slab_free.constprop.0+0xf8/0x1a0 __kasan_slab_free+0x10/0x20 slab_free_freelist_hook+0xf8/0x1a0 kfree+0x148/0x25c kunit_destroy_resource+0x15c/0x1bc string_stream_destroy+0x20/0x80 kunit_do_assertion+0x190/0x1e4 kmalloc_double_kzfree+0x158/0x190 [test_kasan] kunit_try_run_case+0x78/0xa4 kunit_generic_run_threadfn_adapter+0x20/0x2c kthread+0x134/0x144 ret_from_fork+0x10/0x38 ---[ end trace 5acd02cdb9b3d3f0 ]--- but maybe I'm using the kunit tests wrong. It's my first time playing with them. > Signed-off-by: Richard Henderson <richard.hender...@linaro.org> > --- > target/arm/mte_helper.c | 38 +++++++++++++++++--------------------- > 1 file changed, 17 insertions(+), 21 deletions(-) > > diff --git a/target/arm/mte_helper.c b/target/arm/mte_helper.c > index 8be17e1b70..c87717127c 100644 > --- a/target/arm/mte_helper.c > +++ b/target/arm/mte_helper.c > @@ -757,10 +757,10 @@ uint64_t mte_checkN(CPUARMState *env, uint32_t desc, > uint64_t ptr, uintptr_t ra) > { > int mmu_idx, ptr_tag, bit55; > - uint64_t ptr_last, ptr_end, prev_page, next_page; > - uint64_t tag_first, tag_end; > - uint64_t tag_byte_first, tag_byte_end; > - uint32_t esize, total, tag_count, tag_size, n, c; > + uint64_t ptr_last, prev_page, next_page; > + uint64_t tag_first, tag_last; > + uint64_t tag_byte_first, tag_byte_last; > + uint32_t total, tag_count, tag_size, n, c; > uint8_t *mem1, *mem2; > MMUAccessType type; > > @@ -779,29 +779,27 @@ uint64_t mte_checkN(CPUARMState *env, uint32_t desc, > > mmu_idx = FIELD_EX32(desc, MTEDESC, MIDX); > type = FIELD_EX32(desc, MTEDESC, WRITE) ? MMU_DATA_STORE : MMU_DATA_LOAD; > - esize = FIELD_EX32(desc, MTEDESC, ESIZE); > total = FIELD_EX32(desc, MTEDESC, TSIZE); > > /* Find the addr of the end of the access, and of the last element. */ > - ptr_end = ptr + total; > - ptr_last = ptr_end - esize; > + ptr_last = ptr + total - 1; > > /* Round the bounds to the tag granule, and compute the number of tags. > */ > tag_first = QEMU_ALIGN_DOWN(ptr, TAG_GRANULE); > - tag_end = QEMU_ALIGN_UP(ptr_last, TAG_GRANULE); > - tag_count = (tag_end - tag_first) / TAG_GRANULE; > + tag_last = QEMU_ALIGN_DOWN(ptr_last, TAG_GRANULE); > + tag_count = ((tag_last - tag_first) / TAG_GRANULE) + 1; > > /* Round the bounds to twice the tag granule, and compute the bytes. */ > tag_byte_first = QEMU_ALIGN_DOWN(ptr, 2 * TAG_GRANULE); > - tag_byte_end = QEMU_ALIGN_UP(ptr_last, 2 * TAG_GRANULE); > + tag_byte_last = QEMU_ALIGN_DOWN(ptr_last, 2 * TAG_GRANULE); > > /* Locate the page boundaries. */ > prev_page = ptr & TARGET_PAGE_MASK; > next_page = prev_page + TARGET_PAGE_SIZE; > > - if (likely(tag_end - prev_page <= TARGET_PAGE_SIZE)) { > + if (likely(tag_last - prev_page <= TARGET_PAGE_SIZE)) { > /* Memory access stays on one page. */ > - tag_size = (tag_byte_end - tag_byte_first) / (2 * TAG_GRANULE); > + tag_size = ((tag_byte_last - tag_byte_first) / (2 * TAG_GRANULE)) + > 1; > mem1 = allocation_tag_mem(env, mmu_idx, ptr, type, total, > MMU_DATA_LOAD, tag_size, ra); > if (!mem1) { > @@ -815,9 +813,9 @@ uint64_t mte_checkN(CPUARMState *env, uint32_t desc, > mem1 = allocation_tag_mem(env, mmu_idx, ptr, type, next_page - ptr, > MMU_DATA_LOAD, tag_size, ra); > > - tag_size = (tag_byte_end - next_page) / (2 * TAG_GRANULE); > + tag_size = ((tag_byte_last - next_page) / (2 * TAG_GRANULE)) + 1; > mem2 = allocation_tag_mem(env, mmu_idx, next_page, type, > - ptr_end - next_page, > + ptr_last - next_page + 1, > MMU_DATA_LOAD, tag_size, ra); > > /* > @@ -838,15 +836,13 @@ uint64_t mte_checkN(CPUARMState *env, uint32_t desc, > } > > /* > - * If we failed, we know which granule. Compute the element that > - * is first in that granule, and signal failure on that element. > + * If we failed, we know which granule. For the first granule, the > + * failure address is @ptr, the first byte accessed. Otherwise the > + * failure address is the first byte of the nth granule. > */ > if (unlikely(n < tag_count)) { > - uint64_t fail_ofs; > - > - fail_ofs = tag_first + n * TAG_GRANULE - ptr; > - fail_ofs = ROUND_UP(fail_ofs, esize); > - mte_check_fail(env, desc, ptr + fail_ofs, ra); > + uint64_t fault = (n == 0 ? ptr : tag_first + n * TAG_GRANULE); > + mte_check_fail(env, desc, fault, ra); > } > > done: -- Alex Bennée
