On Fri, Jun 10, 2022 at 5:21 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> This reverts commit e5b8d9218951e59df986f627ec93569a0d22149b.
>
> Pages mapped in user-space with PROT_MTE have the allocation tags either
> zeroed or copied/restored to some user values. In order for the kernel
> to access such pages via page_address(), resetting the tag in
> page->flags was necessary. This tag resetting was deferred to
> set_pte_at() -> mte_sync_page_tags() but it can race with another CPU
> reading the flags (via page_to_virt()):
>
> P0 (mte_sync_page_tags): P1 (memcpy from virt_to_page):
> Rflags!=0xff
> Wflags=0xff
> DMB (doesn't help)
> Wtags=0
> Rtags=0 // fault
>
> Since now the post_alloc_hook() function resets the page->flags tag when
> unpoisoning is skipped for user pages (including the __GFP_ZEROTAGS
> case), revert the arm64 commit calling page_kasan_tag_reset().
>
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
> ---
> arch/arm64/kernel/hibernate.c | 5 -----
> arch/arm64/kernel/mte.c | 9 ---------
> arch/arm64/mm/copypage.c | 9 ---------
> arch/arm64/mm/mteswap.c | 9 ---------
> 4 files changed, 32 deletions(-)
>
> diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
> index 2e248342476e..af5df48ba915 100644
> --- a/arch/arm64/kernel/hibernate.c
> +++ b/arch/arm64/kernel/hibernate.c
> @@ -300,11 +300,6 @@ 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);
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index 57b30bcf9f21..7ba4d6fd1f72 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -48,15 +48,6 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte,
> if (!pte_is_tagged)
> 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 page->flags are visible before the tags were updated.
> - */
> - smp_wmb();
> mte_clear_page_tags(page_address(page));
> }
>
> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
> index 0dea80bf6de4..24913271e898 100644
> --- a/arch/arm64/mm/copypage.c
> +++ b/arch/arm64/mm/copypage.c
> @@ -23,15 +23,6 @@ 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);
> - /*
> - * 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 page->flags are visible before the tags were updated.
> - */
> - smp_wmb();
> mte_copy_page_tags(kto, kfrom);
> }
> }
> diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c
> index a9e50e930484..4334dec93bd4 100644
> --- a/arch/arm64/mm/mteswap.c
> +++ b/arch/arm64/mm/mteswap.c
> @@ -53,15 +53,6 @@ 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 page->flags are visible before the tags were updated.
> - */
> - smp_wmb();
> mte_restore_page_tags(page_address(page), tags);
>
> return true;
Acked-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
