Messages in this thread Patch in this message | | | From | andrey.konovalov@linux ... | Subject | [PATCH v2 mm] kasan: reset page tags properly with sampling | Date | Tue, 24 Jan 2023 21:40:09 +0100 |
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From: Andrey Konovalov <andreyknvl@google.com>
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.
Reported-by: Peter Collingbourne <pcc@google.com> Tested-by: Peter Collingbourne <pcc@google.com> Signed-off-by: Andrey Konovalov <andreyknvl@google.com> --- mm/page_alloc.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5514d84cc712..b917aebfd3d0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2471,7 +2471,7 @@ 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); @@ -2498,7 +2498,7 @@ 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); @@ -2516,14 +2516,15 @@ 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) -- 2.25.1
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