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.
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 9 +++++++--
arch/arm64/kernel/mte.c | 16 ++++++++++++++--
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0b10204e72fc..275178a810c1 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -314,8 +314,13 @@ 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))
+ /*
+ * If the PTE would provide user space access to the tags associated
+ * with it then ensure that the MTE tags are synchronised. Exec-only
+ * mappings don't expose tags (instruction fetches don't check tags).
+ */
+ if (system_supports_mte() && pte_present(pte) &&
+ pte_access_permitted(pte, false) && !pte_special(pte))
mte_sync_tags(ptep, pte);
__check_racy_pte_update(mm, ptep, pte);
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index c88e778c2fa9..a604818c52c1 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -33,11 +33,15 @@ 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 *ptep, bool check_swap,
+ bool pte_is_tagged)
{
unsigned long flags;
pte_t old_pte = READ_ONCE(*ptep);
+ if (!is_swap_pte(old_pte) && !pte_is_tagged)
+ return;
+
spin_lock_irqsave(&tag_sync_lock, flags);
/* Recheck with the lock held */
@@ -53,6 +57,9 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
}
}
+ if (!pte_is_tagged)
+ goto out;
+
page_kasan_tag_reset(page);
/*
* We need smp_wmb() in between setting the flags and clearing the
@@ -76,10 +83,15 @@ void mte_sync_tags(pte_t *ptep, pte_t pte)
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_bit(PG_mte_tagged, &page->flags))
- mte_sync_page_tags(page, ptep, check_swap);
+ mte_sync_page_tags(page, ptep, check_swap,
+ pte_is_tagged);
}
}
--
2.20.1
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