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From: Andrey Konovalov <andreyknvl@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-arm-kernel@lists.infradead.org,
	Marco Elver <elver@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Branislav Rankov <Branislav.Rankov@arm.com>,
	kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Alexander Potapenko <glider@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH mm v11 26/42] arm64: mte: Reset the page tag in page->flags
Date: Mon, 23 Nov 2020 21:07:50 +0100
Message-ID: <9073d4e973747a6f78d5bdd7ebe17f290d087096.1606161801.git.andreyknvl@google.com> (raw)
In-Reply-To: <cover.1606161801.git.andreyknvl@google.com>

From: Vincenzo Frascino <vincenzo.frascino@arm.com>

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.

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>
---
Change-Id: I8451d438bb63364de2a3e68041e3a27866921d4e
---
 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 insertions(+)

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 8f99c65837fd..86d554ce98b6 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;
-- 
2.29.2.454.gaff20da3a2-goog


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  parent reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-23 20:07 [PATCH mm v11 00/42] kasan: add hardware tag-based mode for arm64 Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 01/42] kasan: drop unnecessary GPL text from comment headers Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 02/42] kasan: KASAN_VMALLOC depends on KASAN_GENERIC Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 03/42] kasan: group vmalloc code Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 04/42] kasan: shadow declarations only for software modes Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 05/42] kasan: rename (un)poison_shadow to (un)poison_range Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 06/42] kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_* Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 07/42] kasan: only build init.c for software modes Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 08/42] kasan: split out shadow.c from common.c Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 09/42] kasan: define KASAN_MEMORY_PER_SHADOW_PAGE Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 10/42] kasan: rename report and tags files Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 11/42] kasan: don't duplicate config dependencies Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 12/42] kasan: hide invalid free check implementation Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 13/42] kasan: decode stack frame only with KASAN_STACK_ENABLE Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 14/42] kasan, arm64: only init shadow for software modes Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 15/42] kasan, arm64: only use kasan_depth " Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 16/42] kasan, arm64: move initialization message Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 17/42] kasan, arm64: rename kasan_init_tags and mark as __init Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 18/42] kasan: rename addr_has_shadow to addr_has_metadata Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 19/42] kasan: rename print_shadow_for_address to print_memory_metadata Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 20/42] kasan: rename SHADOW layout macros to META Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 21/42] kasan: separate metadata_fetch_row for each mode Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 22/42] kasan, arm64: don't allow SW_TAGS with ARM64_MTE Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 23/42] kasan: introduce CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 24/42] arm64: Enable armv8.5-a asm-arch option Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 25/42] arm64: mte: Add in-kernel MTE helpers Andrey Konovalov
2020-11-23 20:07 ` Andrey Konovalov [this message]
2020-11-23 20:07 ` [PATCH mm v11 27/42] arm64: mte: Add in-kernel tag fault handler Andrey Konovalov
2020-12-03 10:26   ` Catalin Marinas
2020-12-03 10:39     ` Vincenzo Frascino
2020-11-23 20:07 ` [PATCH mm v11 28/42] arm64: kasan: Allow enabling in-kernel MTE Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 29/42] arm64: mte: Convert gcr_user into an exclude mask Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 30/42] arm64: mte: Switch GCR_EL1 in kernel entry and exit Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 31/42] kasan, mm: untag page address in free_reserved_area Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 32/42] arm64: kasan: Align allocations for HW_TAGS Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 33/42] arm64: kasan: Add arch layer for memory tagging helpers Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 34/42] kasan: define KASAN_GRANULE_SIZE for HW_TAGS Andrey Konovalov
2020-11-23 20:07 ` [PATCH mm v11 35/42] kasan, x86, s390: update undef CONFIG_KASAN Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 36/42] kasan, arm64: expand CONFIG_KASAN checks Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 37/42] kasan, arm64: implement HW_TAGS runtime Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 38/42] kasan, arm64: print report from tag fault handler Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 39/42] kasan, mm: reset tags when accessing metadata Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 40/42] kasan, arm64: enable CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 41/42] kasan: add documentation for hardware tag-based mode Andrey Konovalov
2020-11-23 20:08 ` [PATCH mm v11 42/42] kselftest/arm64: Check GCR_EL1 after context switch Andrey Konovalov

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