Commit 69e3b846 authored by Steven Price's avatar Steven Price Committed by Marc Zyngier
Browse files

arm64: mte: Sync tags for pages where PTE is untagged 



A KVM guest could store tags in a page even if the VMM hasn't mapped
the page with PROT_MTE. So when restoring pages from swap we will
need to check to see if there are any saved tags even if !pte_tagged().

However don't check pages for which pte_access_permitted() returns false
as these will not have been swapped out.

Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarSteven Price <steven.price@arm.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210621111716.37157-2-steven.price@arm.com
parent 8124c8a6

arch/arm64/include/asm/mte.h

+2 −2
Original line number Diff line number Diff line
@@ -37,7 +37,7 @@ void mte_free_tag_storage(char *storage); 
/* track which pages have valid allocation tags */

#define PG_mte_tagged	PG_arch_2



void mte_sync_tags(pte_t *ptep, pte_t pte);

void mte_sync_tags(pte_t old_pte, pte_t pte);

void mte_copy_page_tags(void *kto, const void *kfrom);

void mte_thread_init_user(void);

void mte_thread_switch(struct task_struct *next);
@@ -53,7 +53,7 @@ int mte_ptrace_copy_tags(struct task_struct *child, long request, 
/* unused if !CONFIG_ARM64_MTE, silence the compiler */

#define PG_mte_tagged	0



static inline void mte_sync_tags(pte_t *ptep, pte_t pte)

static inline void mte_sync_tags(pte_t old_pte, pte_t pte)

{

}

static inline void mte_copy_page_tags(void *kto, const void *kfrom)

arch/arm64/include/asm/pgtable.h

+19 −3
Original line number Diff line number Diff line
@@ -314,9 +314,25 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, 
	if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))

		__sync_icache_dcache(pte);



	if (system_supports_mte() &&

	    pte_present(pte) && pte_tagged(pte) && !pte_special(pte))

		mte_sync_tags(ptep, pte);

	/*

	 * If the PTE would provide user space access to the tags associated

	 * with it then ensure that the MTE tags are synchronised.  Although

	 * pte_access_permitted() returns false for exec only mappings, they

	 * don't expose tags (instruction fetches don't check tags).

	 */

	if (system_supports_mte() && pte_access_permitted(pte, false) &&

	    !pte_special(pte)) {

		pte_t old_pte = READ_ONCE(*ptep);

		/*

		 * We only need to synchronise if the new PTE has tags enabled

		 * or if swapping in (in which case another mapping may have

		 * set tags in the past even if this PTE isn't tagged).

		 * (!pte_none() && !pte_present()) is an open coded version of

		 * is_swap_pte()

		 */

		if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte)))

			mte_sync_tags(old_pte, pte);

	}



	__check_racy_pte_update(mm, ptep, pte);

arch/arm64/kernel/mte.c

+13 −5
Original line number Diff line number Diff line
@@ -32,10 +32,9 @@ DEFINE_STATIC_KEY_FALSE(mte_async_mode); 
EXPORT_SYMBOL_GPL(mte_async_mode);

#endif



static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)

static void mte_sync_page_tags(struct page *page, pte_t old_pte,

			       bool check_swap, bool pte_is_tagged)

{

	pte_t old_pte = READ_ONCE(*ptep);



	if (check_swap && is_swap_pte(old_pte)) {

		swp_entry_t entry = pte_to_swp_entry(old_pte);
@@ -43,6 +42,9 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) 
			return;

	}



	if (!pte_is_tagged)

		return;



	page_kasan_tag_reset(page);

	/*

	 * We need smp_wmb() in between setting the flags and clearing the
@@ -55,16 +57,22 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) 
	mte_clear_page_tags(page_address(page));

}



void mte_sync_tags(pte_t *ptep, pte_t pte)

void mte_sync_tags(pte_t old_pte, pte_t pte)

{

	struct page *page = pte_page(pte);

	long i, nr_pages = compound_nr(page);

	bool check_swap = nr_pages == 1;

	bool pte_is_tagged = pte_tagged(pte);



	/* Early out if there's nothing to do */

	if (!check_swap && !pte_is_tagged)

		return;



	/* if PG_mte_tagged is set, tags have already been initialised */

	for (i = 0; i < nr_pages; i++, page++) {

		if (!test_and_set_bit(PG_mte_tagged, &page->flags))

			mte_sync_page_tags(page, ptep, check_swap);

			mte_sync_page_tags(page, old_pte, check_swap,

					   pte_is_tagged);

	}

}