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authorVincenzo Frascino <vincenzo.frascino@arm.com>2020-12-10 15:42:11 +1100
committerStephen Rothwell <sfr@canb.auug.org.au>2020-12-16 18:02:59 +1100
commit54053196a429e2e8e56bc70378ef0a23d78a1935 (patch)
treeebd84821330c71d07f5dcc6314ba737ed95fdd12
parenta6bdf8dc80f696a9108e8e610e6c3c86774e066f (diff)
downloadlinux-54053196a429e2e8e56bc70378ef0a23d78a1935.tar.gz
arm64: mte: reset the page tag in page->flags
The hardware tag-based KASAN for compatibility with the other modes stores the tag associated to a page in page->flags. Due to this the kernel faults on access when it allocates a page with an initial tag and the user changes the tags. Reset the tag associated by the kernel to a page in all the meaningful places to prevent kernel faults on access. Note: An alternative to this approach could be to modify page_to_virt(). This though could end up being racy, in fact if a CPU checks the PG_mte_tagged bit and decides that the page is not tagged but another CPU maps the same with PROT_MTE and becomes tagged the subsequent kernel access would fail. Link: https://lkml.kernel.org/r/9073d4e973747a6f78d5bdd7ebe17f290d087096.1606161801.git.andreyknvl@google.com Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Branislav Rankov <Branislav.Rankov@arm.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Marco Elver <elver@google.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
-rw-r--r--arch/arm64/kernel/hibernate.c5
-rw-r--r--arch/arm64/kernel/mte.c9
-rw-r--r--arch/arm64/mm/copypage.c9
-rw-r--r--arch/arm64/mm/mteswap.c9
4 files changed, 32 insertions, 0 deletions
diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index 42003774d261..9c9f47e9f7f4 100644
--- a/arch/arm64/kernel/hibernate.c
+++ b/arch/arm64/kernel/hibernate.c
@@ -371,6 +371,11 @@ 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 78f81c459cb1..3a6216b0002e 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -34,6 +34,15 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
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 70a71f38b6a9..b5447e53cd73 100644
--- a/arch/arm64/mm/copypage.c
+++ b/arch/arm64/mm/copypage.c
@@ -23,6 +23,15 @@ 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 c52c1847079c..7c4ef56265ee 100644
--- a/arch/arm64/mm/mteswap.c
+++ b/arch/arm64/mm/mteswap.c
@@ -53,6 +53,15 @@ 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;