| Message ID | 20220517180945.756303-4-catalin.marinas@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kasan: Fix ordering between MTE tag colouring and page->flags | expand |
On Tue, May 17, 2022 at 8:09 PM Catalin Marinas <catalin.marinas@arm.com> wrote: > > This reverts commit e5b8d9218951e59df986f627ec93569a0d22149b. > > On a system with MTE and KASAN_HW_TAGS enabled, when a page is allocated > kasan_unpoison_pages() sets a random tag and saves it in page->flags. > page_to_virt() re-creates the correct tagged pointer. > > If such page is mapped in user-space with PROT_MTE, the architecture > code will set the tag to 0 and a subsequent page_to_virt() dereference > will fault. The reverted commit aimed to fix this by resetting the tag > in page->flags so that it is 0xff (match-all, not faulting). However, > setting the tags and flags can race with another CPU reading the flags > (page_to_virt()) and barriers can't help: > > 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 clearing the flags in the arch code doesn't help, revert the patch > altogether. In addition, remove the page_kasan_tag_reset() call in > tag_clear_highpage() since the core kasan code should take care of > resetting the page tag. > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> > Cc: Andrey Konovalov <andreyknvl@gmail.com> > Cc: Peter Collingbourne <pcc@google.com> > --- > arch/arm64/kernel/hibernate.c | 5 ----- > arch/arm64/kernel/mte.c | 9 --------- > arch/arm64/mm/copypage.c | 9 --------- > arch/arm64/mm/fault.c | 1 - > arch/arm64/mm/mteswap.c | 9 --------- > 5 files changed, 33 deletions(-) > > diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c > index 6328308be272..7754ef328657 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 78b3e0f8e997..90994aca54f3 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -47,15 +47,6 @@ 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 b5447e53cd73..70a71f38b6a9 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/fault.c b/arch/arm64/mm/fault.c > index 77341b160aca..f2f21cd6d43f 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -926,6 +926,5 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma, > void tag_clear_highpage(struct page *page) > { > mte_zero_clear_page_tags(page_address(page)); > - page_kasan_tag_reset(page); This change is not a part of e5b8d9218951e59df986f627ec93569a0d22149b revert. I think it should go into a separate commit. > set_bit(PG_mte_tagged, &page->flags); > } > 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;
diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c index 6328308be272..7754ef328657 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 78b3e0f8e997..90994aca54f3 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -47,15 +47,6 @@ 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 b5447e53cd73..70a71f38b6a9 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/fault.c b/arch/arm64/mm/fault.c index 77341b160aca..f2f21cd6d43f 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -926,6 +926,5 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma, void tag_clear_highpage(struct page *page) { mte_zero_clear_page_tags(page_address(page)); - page_kasan_tag_reset(page); set_bit(PG_mte_tagged, &page->flags); } 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;
This reverts commit e5b8d9218951e59df986f627ec93569a0d22149b. On a system with MTE and KASAN_HW_TAGS enabled, when a page is allocated kasan_unpoison_pages() sets a random tag and saves it in page->flags. page_to_virt() re-creates the correct tagged pointer. If such page is mapped in user-space with PROT_MTE, the architecture code will set the tag to 0 and a subsequent page_to_virt() dereference will fault. The reverted commit aimed to fix this by resetting the tag in page->flags so that it is 0xff (match-all, not faulting). However, setting the tags and flags can race with another CPU reading the flags (page_to_virt()) and barriers can't help: 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 clearing the flags in the arch code doesn't help, revert the patch altogether. In addition, remove the page_kasan_tag_reset() call in tag_clear_highpage() since the core kasan code should take care of resetting the page tag. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Andrey Konovalov <andreyknvl@gmail.com> Cc: Peter Collingbourne <pcc@google.com> --- arch/arm64/kernel/hibernate.c | 5 ----- arch/arm64/kernel/mte.c | 9 --------- arch/arm64/mm/copypage.c | 9 --------- arch/arm64/mm/fault.c | 1 - arch/arm64/mm/mteswap.c | 9 --------- 5 files changed, 33 deletions(-)