On Thu, Apr 20, 2023 at 02:43:27PM -0700, Peter Collingbourne wrote:
The mte_sync_page_tags() function sets PG_mte_tagged if it initializes page tags. Then we return to mte_sync_tags(), which sets PG_mte_tagged again. At best, this is redundant. However, it is possible for mte_sync_page_tags() to return without having initialized tags for the page, i.e. in the case where check_swap is true (non-compound page), is_swap_pte(old_pte) is false and pte_is_tagged is false. So at worst, we set PG_mte_tagged on a page with uninitialized tags. This can happen if, for example, page migration causes a PTE for an untagged page to be replaced. If the userspace program subsequently uses mprotect() to enable PROT_MTE for that page, the uninitialized tags will be exposed to userspace.
Fix it by removing the redundant call to set_page_mte_tagged().
Fixes: e059853d14ca ("arm64: mte: Fix/clarify the PG_mte_tagged semantics") Signed-off-by: Peter Collingbourne pcc@google.com Cc: stable@vger.kernel.org # 6.1 Link: https://linux-review.googlesource.com/id/Ib02d004d435b2ed87603b858ef7480f7b1...
arch/arm64/kernel/mte.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index f5bcb0dc6267..7e89968bd282 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -66,13 +66,10 @@ void mte_sync_tags(pte_t old_pte, pte_t pte) return; /* if PG_mte_tagged is set, tags have already been initialised */
- for (i = 0; i < nr_pages; i++, page++) {
if (!page_mte_tagged(page)) {
- for (i = 0; i < nr_pages; i++, page++)
if (!page_mte_tagged(page)) mte_sync_page_tags(page, old_pte, check_swap, pte_is_tagged);
set_page_mte_tagged(page);}- }
It makes sense, not sure why I added it here when mte_sync_page_tags() was already setting the flag if needed.
Reviewed-by: Catalin Marinas catalin.marinas@arm.com