Consider the following sequence of events:
1) A page in a PROT_READ|PROT_WRITE VMA is faulted. 2) Page migration allocates a page with the KASAN allocator, causing it to receive a non-match-all tag, and uses it to replace the page faulted in 1. 3) The program uses mprotect() to enable PROT_MTE on the page faulted in 1.
As a result of step 3, we are left with a non-match-all tag for a page with tags accessible to userspace, which can lead to the same kind of tag check faults that commit e74a68468062 ("arm64: Reset KASAN tag in copy_highpage with HW tags only") intended to fix.
The general invariant that we have for pages in a VMA with VM_MTE_ALLOWED is that they cannot have a non-match-all tag. As a result of step 2, the invariant is broken. This means that the fix in the referenced commit was incomplete and we also need to reset the tag for pages without PG_mte_tagged.
Fixes: e5b8d9218951 ("arm64: mte: reset the page tag in page->flags") Cc: stable@vger.kernel.org # 5.15 Link: https://linux-review.googlesource.com/id/I7409cdd41acbcb215c2a7417c1e50d37b8... Signed-off-by: Peter Collingbourne pcc@google.com Reviewed-by: Catalin Marinas catalin.marinas@arm.com Link: https://lore.kernel.org/r/20230420210945.2313627-1-pcc@google.com Signed-off-by: Will Deacon will@kernel.org (cherry picked from commit 2efbafb91e12ff5a16cbafb0085e4c10c3fca493) --- arch/arm64/mm/copypage.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c index 0dea80bf6de4..b44931deb227 100644 --- a/arch/arm64/mm/copypage.c +++ b/arch/arm64/mm/copypage.c @@ -21,9 +21,10 @@ void copy_highpage(struct page *to, struct page *from)
copy_page(kto, kfrom);
+ page_kasan_tag_reset(to); + 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