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From:   Alexandru Elisei <alexandru.elisei@arm.com>
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Subject: [PATCH RFC v2 14/27] arm64: mte: Disable dynamic tag storage management if HW KASAN is enabled
Date:   Sun, 19 Nov 2023 16:57:08 +0000
Message-Id: <20231119165721.9849-15-alexandru.elisei@arm.com>
In-Reply-To: <20231119165721.9849-1-alexandru.elisei@arm.com>
References: <20231119165721.9849-1-alexandru.elisei@arm.com>
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To be able to reserve the tag storage associated with a page requires that
the tag storage page can be migrated.

When HW KASAN is enabled, the kernel allocates pages, which are now tagged,
in non-preemptible contexts, which can make reserving the associate tag
storage impossible.

Keep the tag storage pages reserved if HW KASAN is enabled.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/kernel/mte_tag_storage.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
index 427f4f1909f3..8b9bedf7575d 100644
--- a/arch/arm64/kernel/mte_tag_storage.c
+++ b/arch/arm64/kernel/mte_tag_storage.c
@@ -308,6 +308,19 @@ static int __init mte_tag_storage_activate_regions(void)
 		goto out_disabled;
 	}
 
+	/*
+	 * The kernel allocates memory in non-preemptible contexts, which makes
+	 * migration impossible when reserving the associated tag storage.
+	 *
+	 * The check is safe to make because KASAN HW tags are enabled before
+	 * the rest of the init functions are called, in smp_prepare_boot_cpu().
+	 */
+	if (kasan_hw_tags_enabled()) {
+		pr_info("KASAN HW tags incompatible with MTE tag storage management");
+		ret = 0;
+		goto out_disabled;
+	}
+
 	for (i = 0; i < num_tag_regions; i++) {
 		tag_range = &tag_regions[i].tag_range;
 		for (pfn = tag_range->start; pfn <= tag_range->end; pfn += pageblock_nr_pages)
-- 
2.42.1