arm64: kasan: Revert "arm64: mte: reset the page tag in page->flags"

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@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>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20220610152141.2148929-5-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index 2e248342476eaff93a95160aa80abfb3d1c6f63e..af5df48ba915b9274211f66c33f4e61fcbe89a1e 100644 (file)
--- 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 f6b00743c3994a19f78be4b81b52a6c570800ec3..b2b730233274b72f4e1c619d39a0e68d22835f13 100644 (file)
--- 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 0dea80bf6de469e6ab3d5b584d451cf100e77e94..24913271e898c121a9083610144ec640804f02c0 100644 (file)
--- 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 a9e50e930484aa3ce7e09f3d9344f7a72b08de6a..4334dec93bd441eb285d27b97d2b86cfdf1d00c0 100644 (file)
--- 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;