Commit e5b8d921 authored by Vincenzo Frascino's avatar Vincenzo Frascino Committed by Linus Torvalds
Browse files

arm64: mte: reset the page tag in page->flags 

The hardware tag-based KASAN for compatibility with the other modes stores
the tag associated to a page in page->flags.  Due to this the kernel
faults on access when it allocates a page with an initial tag and the user
changes the tags.

Reset the tag associated by the kernel to a page in all the meaningful
places to prevent kernel faults on access.

Note: An alternative to this approach could be to modify page_to_virt().
This though could end up being racy, in fact if a CPU checks the
PG_mte_tagged bit and decides that the page is not tagged but another CPU
maps the same with PROT_MTE and becomes tagged the subsequent kernel
access would fail.

Link: https://lkml.kernel.org/r/9073d4e973747a6f78d5bdd7ebe17f290d087096.1606161801.git.andreyknvl@google.com


Signed-off-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Tested-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 85f49cae

arch/arm64/kernel/hibernate.c

+5 −0
Original line number Diff line number Diff line
@@ -371,6 +371,11 @@ static void swsusp_mte_restore_tags(void) 
		unsigned long pfn = xa_state.xa_index;

		struct page *page = pfn_to_online_page(pfn);



		/*

		 * It is not required to invoke page_kasan_tag_reset(page)

		 * at this point since the tags stored in page->flags are

		 * already restored.

		 */

		mte_restore_page_tags(page_address(page), tags);



		mte_free_tag_storage(tags);

arch/arm64/kernel/mte.c

+9 −0
Original line number Diff line number Diff line
@@ -34,6 +34,15 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) 
			return;

	}



	page_kasan_tag_reset(page);

	/*

	 * We need smp_wmb() in between setting the flags and clearing the

	 * tags because if another thread reads page->flags and builds a

	 * tagged address out of it, there is an actual dependency to the

	 * memory access, but on the current thread we do not guarantee that

	 * the new page->flags are visible before the tags were updated.

	 */

	smp_wmb();

	mte_clear_page_tags(page_address(page));

}

arch/arm64/mm/copypage.c

+9 −0
Original line number Diff line number Diff line
@@ -23,6 +23,15 @@ void copy_highpage(struct page *to, struct page *from) 


	if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) {

		set_bit(PG_mte_tagged, &to->flags);

		page_kasan_tag_reset(to);

		/*

		 * We need smp_wmb() in between setting the flags and clearing the

		 * tags because if another thread reads page->flags and builds a

		 * tagged address out of it, there is an actual dependency to the

		 * memory access, but on the current thread we do not guarantee that

		 * the new page->flags are visible before the tags were updated.

		 */

		smp_wmb();

		mte_copy_page_tags(kto, kfrom);

	}

}

arch/arm64/mm/mteswap.c

+9 −0
Original line number Diff line number Diff line
@@ -53,6 +53,15 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) 
	if (!tags)

		return false;



	page_kasan_tag_reset(page);

	/*

	 * We need smp_wmb() in between setting the flags and clearing the

	 * tags because if another thread reads page->flags and builds a

	 * tagged address out of it, there is an actual dependency to the

	 * memory access, but on the current thread we do not guarantee that

	 * the new page->flags are visible before the tags were updated.

	 */

	smp_wmb();

	mte_restore_page_tags(page_address(page), tags);



	return true;