Commit 216da24f authored by Vincenzo Frascino's avatar Vincenzo Frascino
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.

Signed-off-by: Vincenzo Frascino's avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
---
Change-Id: I8451d438bb63364de2a3e68041e3a27866921d4e
parent 0f53789d
......@@ -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);
......
......@@ -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 new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_clear_page_tags(page_address(page));
}
......
......@@ -23,6 +23,7 @@ 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);
mte_copy_page_tags(kto, kfrom);
}
}
......
......@@ -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 new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_restore_page_tags(page_address(page), tags);
return true;
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment