From: Andrey Konovalov Date: Tue, 24 Jan 2023 20:35:26 +0000 (+0100) Subject: kasan: reset page tags properly with sampling X-Git-Tag: v6.6.17~5460^2~195 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=420ef683b5217338bc679c33fd9361b52f53a526;p=platform%2Fkernel%2Flinux-rpi.git kasan: reset page tags properly with sampling The implementation of page_alloc poisoning sampling assumed that tag_clear_highpage resets page tags for __GFP_ZEROTAGS allocations. However, this is no longer the case since commit 70c248aca9e7 ("mm: kasan: Skip unpoisoning of user pages"). This leads to kernel crashes when MTE-enabled userspace mappings are used with Hardware Tag-Based KASAN enabled. Reset page tags for __GFP_ZEROTAGS allocations in post_alloc_hook(). Also clarify and fix related comments. [andreyknvl@google.com: update comment] Link: https://lkml.kernel.org/r/5dbd866714b4839069e2d8469ac45b60953db290.1674592780.git.andreyknvl@google.com Link: https://lkml.kernel.org/r/24ea20c1b19c2b4b56cf9f5b354915f8dbccfc77.1674592496.git.andreyknvl@google.com Fixes: 44383cef54c0 ("kasan: allow sampling page_alloc allocations for HW_TAGS") Signed-off-by: Andrey Konovalov Reported-by: Peter Collingbourne Tested-by: Peter Collingbourne Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Marco Elver Signed-off-by: Andrew Morton --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 717f12e83b85..5ebce58026f1 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2476,7 +2476,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order, bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) && !should_skip_init(gfp_flags); bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS); - bool reset_tags = !zero_tags; + bool reset_tags = true; int i; set_page_private(page, 0); @@ -2503,7 +2503,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order, * (which happens only when memory should be initialized as well). */ if (zero_tags) { - /* Initialize both memory and tags. */ + /* Initialize both memory and memory tags. */ for (i = 0; i != 1 << order; ++i) tag_clear_highpage(page + i); @@ -2521,14 +2521,15 @@ inline void post_alloc_hook(struct page *page, unsigned int order, } else { /* * KASAN decided to exclude this allocation from being - * poisoned due to sampling. Skip poisoning as well. + * (un)poisoned due to sampling. Make KASAN skip + * poisoning when the allocation is freed. */ SetPageSkipKASanPoison(page); } } /* - * If memory tags have not been set, reset the page tags to ensure - * page_address() dereferencing does not fault. + * If memory tags have not been set by KASAN, reset the page tags to + * ensure page_address() dereferencing does not fault. */ if (reset_tags) { for (i = 0; i != 1 << order; ++i)