On Fri, 2022-06-10 at 16:21 +0100, Catalin Marinas wrote: > Hi, > > That's a second attempt on fixing the race race between setting the > allocation (in-memory) tags in a page and the corresponding logical > tag > in page->flags. Initial version here: > > https://lore.kernel.org/r/20220517180945.756303-1-catalin.marinas@xxxxxxx > > This new series does not introduce any new GFP flags but instead > always > skips unpoisoning of the user pages (we already skip the poisoning on > free). Any unpoisoned page will have the page->flags tag reset. > > For the background: > > On a system with MTE and KASAN_HW_TAGS enabled, when a page is > allocated > kasan_unpoison_pages() sets a random tag and saves it in page->flags > so > that page_to_virt() re-creates the correct tagged pointer. We need to > ensure that the in-memory tags are visible before setting the > page->flags: > > P0 (__kasan_unpoison_range): P1 (access via virt_to_page): > Wtags=x Rflags=x > | | > | DMB | address dependency > V V > Wflags=x Rtags=x > > The first patch changes the order of page unpoisoning with the tag > storing in page->flags. page_kasan_tag_set() has the right barriers > through try_cmpxchg(). > > If a page is mapped in user-space with PROT_MTE, the architecture > code > will set the allocation tag to 0 and a subsequent page_to_virt() > dereference will fault. We currently try to fix this by resetting the > tag in page->flags so that it is 0xff (match-all, not faulting). > However, setting the tags and flags can race with another CPU reading > the flags (page_to_virt()) and barriers can't help, e.g.: > > P0 (mte_sync_page_tags): P1 (memcpy from virt_to_page): > Rflags!=0xff > Wflags=0xff > DMB (doesn't help) > Wtags=0 > Rtags=0 // fault > > Since clearing the flags in the arch code doesn't work, to do this at > page allocation time when __GFP_SKIP_KASAN_UNPOISON is passed. > > Thanks. > > Catalin Marinas (4): > mm: kasan: Ensure the tags are visible before the tag in page- > >flags > mm: kasan: Skip unpoisoning of user pages > mm: kasan: Skip page unpoisoning only if __GFP_SKIP_KASAN_UNPOISON > arm64: kasan: Revert "arm64: mte: reset the page tag in page- > >flags" > > arch/arm64/kernel/hibernate.c | 5 ----- > arch/arm64/kernel/mte.c | 9 --------- > arch/arm64/mm/copypage.c | 9 --------- > arch/arm64/mm/fault.c | 1 - > arch/arm64/mm/mteswap.c | 9 --------- > include/linux/gfp.h | 2 +- > mm/kasan/common.c | 3 ++- > mm/page_alloc.c | 19 ++++++++++--------- > 8 files changed, 13 insertions(+), 44 deletions(-) > Hi kasan maintainers, We hit the following issue on the android-6.1 devices with MTE and HW tag kasan enabled. I observe that the anon flag doesn't have skip_kasan_poison and skip_kasan_unpoison flag and kasantag is weird. AFAIK, kasantag of anon flag needs to be 0x0. [ 71.953938] [T1403598] FramePolicy: [name:report&]========================================================= ========= [ 71.955305] [T1403598] FramePolicy: [name:report&]BUG: KASAN: invalid-access in copy_page+0x10/0xd0 [ 71.956476] [T1403598] FramePolicy: [name:report&]Read at addr f0ffff81332a8000 by task FramePolicy/3598 [ 71.957673] [T1403598] FramePolicy: [name:report_hw_tags&]Pointer tag: [f0], memory tag: [ff] [ 71.958746] [T1403598] FramePolicy: [name:report&] [ 71.959354] [T1403598] FramePolicy: CPU: 4 PID: 3598 Comm: FramePolicy Tainted: G S W OE 6.1.0-mainline-android14-0- ga8a53f83b9e4 #1 [ 71.960978] [T1403598] FramePolicy: Hardware name: MT6985(ENG) (DT) [ 71.961767] [T1403598] FramePolicy: Call trace: [ 71.962338] [T1403598] FramePolicy: dump_backtrace+0x108/0x158 [ 71.963097] [T1403598] FramePolicy: show_stack+0x20/0x48 [ 71.963782] [T1403598] FramePolicy: dump_stack_lvl+0x6c/0x88 [ 71.964512] [T1403598] FramePolicy: print_report+0x2cc/0xa64 [ 71.965263] [T1403598] FramePolicy: kasan_report+0xb8/0x138 [ 71.965986] [T1403598] FramePolicy: __do_kernel_fault+0xd4/0x248 [ 71.966782] [T1403598] FramePolicy: do_bad_area+0x38/0xe8 [ 71.967484] [T1403598] FramePolicy: do_tag_check_fault+0x24/0x38 [ 71.968261] [T1403598] FramePolicy: do_mem_abort+0x48/0xb0 [ 71.968973] [T1403598] FramePolicy: el1_abort+0x44/0x68 [ 71.969646] [T1403598] FramePolicy: el1h_64_sync_handler+0x68/0xb8 [ 71.970440] [T1403598] FramePolicy: el1h_64_sync+0x68/0x6c [ 71.971146] [T1403598] FramePolicy: copy_page+0x10/0xd0 [ 71.971824] [T1403598] FramePolicy: copy_user_highpage+0x20/0x40 [ 71.972603] [T1403598] FramePolicy: wp_page_copy+0xd0/0x9f8 [ 71.973344] [T1403598] FramePolicy: do_wp_page+0x374/0x3b0 [ 71.974056] [T1403598] FramePolicy: handle_mm_fault+0x3ec/0x119c [ 71.974833] [T1403598] FramePolicy: do_page_fault+0x344/0x4ac [ 71.975583] [T1403598] FramePolicy: do_mem_abort+0x48/0xb0 [ 71.976294] [T1403598] FramePolicy: el0_da+0x4c/0xe0 [ 71.976934] [T1403598] FramePolicy: el0t_64_sync_handler+0xd4/0xfc [ 71.977725] [T1403598] FramePolicy: el0t_64_sync+0x1a0/0x1a4 [ 71.978451] [T1403598] FramePolicy: [name:report&] [ 71.979057] [T1403598] FramePolicy: [name:report&]The buggy address belongs to the physical page: [ 71.980173] [T1403598] FramePolicy: [name:debug&]page:fffffffe04ccaa00 refcount:14 mapcount:13 mapping:0000000000000000 index:0x7884c74 pfn:0x1732a8 [ 71.981849] [T1403598] FramePolicy: [name:debug&]memcg:faffff80c0241000 [ 71.982680] [T1403598] FramePolicy: [name:debug&]anon flags: 0x43c000000048003e(referenced|uptodate|dirty|lru|active|swapbacked|arch _2|zone=1|kasantag=0xf) [ 71.984446] [T1403598] FramePolicy: raw: 43c000000048003e fffffffe04b99648 fffffffe04cca308 f2ffff8103390831 [ 71.985684] [T1403598] FramePolicy: raw: 0000000007884c74 0000000000000000 0000000e0000000c faffff80c0241000 [ 71.986919] [T1403598] FramePolicy: [name:debug&]page dumped because: kasan: bad access detected [ 71.988022] [T1403598] FramePolicy: [name:report&] [ 71.988624] [T1403598] FramePolicy: [name:report&]Memory state around the buggy address: [ 71.989641] [T1403598] FramePolicy: ffffff81332a7e00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe [ 71.990811] [T1403598] FramePolicy: ffffff81332a7f00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe [ 71.991982] [T1403598] FramePolicy: >ffffff81332a8000: ff ff ff ff f0 f0 fc fc fc fc fc fc fc f0 f0 f3 [ 71.993149] [T1403598] FramePolicy: [name:report&] ^ [ 71.993972] [T1403598] FramePolicy: ffffff81332a8100: f3 f3 f3 f3 f3 f3 f0 f0 f8 f8 f8 f8 f8 f8 f8 f0 [ 71.995141] [T1403598] FramePolicy: ffffff81332a8200: f0 fb fb fb fb fb fb fb f0 f0 fe fe fe fe fe fe [ 71.996332] [T1403598] FramePolicy: [name:report&]========================================================= ========= Originally, I suspect that some userspace pages have been migrated so the page->flags will be lost and page->flags is re-generated by alloc_pages(). I try the following diff, but it didn't help. diff --git a/mm/migrate.c b/mm/migrate.c index dff333593a8a..ed2065908418 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -51,6 +51,7 @@ #include <linux/random.h> #include <linux/sched/sysctl.h> #include <linux/memory-tiers.h> +#include <linux/kasan.h> #include <asm/tlbflush.h> @@ -611,6 +612,14 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) if (!folio_test_hugetlb(folio)) mem_cgroup_migrate(folio, newfolio); + +#ifdef CONFIG_KASAN_HW_TAGS + if (kasan_hw_tags_enabled()) { + if (folio_test_skip_kasan_poison(folio)) + folio_set_skip_kasan_poison(newfolio); + page_kasan_tag_set(&newfolio->page, page_kasan_tag(&folio->page)); + } +#endif } EXPORT_SYMBOL(folio_migrate_flags); After I revert this patchset (4 patches), this issue disappear. >
