[PATCH RFC v2 14/27] arm64: mte: Disable dynamic tag storage management if HW KASAN is enabled

Alexandru Elisei
2023-11-19T18:00:33Z

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