s390: add support for KFENCE

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
[hca@linux.ibm.com: simplify/rework code]
Link: https://lore.kernel.org/r/20210728190254.3921642-4-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/arch/s390/include/asm/kfence.h b/arch/s390/include/asm/kfence.h
new file mode 100644
index 000000000000..d55ba878378b
--- /dev/null
+++ b/arch/s390/include/asm/kfence.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_S390_KFENCE_H
+#define _ASM_S390_KFENCE_H
+
+#include <linux/mm.h>
+#include <linux/kfence.h>
+#include <asm/set_memory.h>
+#include <asm/page.h>
+
+void __kernel_map_pages(struct page *page, int numpages, int enable);
+
+static __always_inline bool arch_kfence_init_pool(void)
+{
+	return true;
+}
+
+#define arch_kfence_test_address(addr) ((addr) & PAGE_MASK)
+
+/*
+ * Do not split kfence pool to 4k mapping with arch_kfence_init_pool(),
+ * but earlier where page table allocations still happen with memblock.
+ * Reason is that arch_kfence_init_pool() gets called when the system
+ * is still in a limbo state - disabling and enabling bottom halves is
+ * not yet allowed, but that is what our page_table_alloc() would do.
+ */
+static __always_inline void kfence_split_mapping(void)
+{
+#ifdef CONFIG_KFENCE
+	unsigned long pool_pages = KFENCE_POOL_SIZE >> PAGE_SHIFT;
+
+	set_memory_4k((unsigned long)__kfence_pool, pool_pages);
+#endif
+}
+
+static inline bool kfence_protect_page(unsigned long addr, bool protect)
+{
+	__kernel_map_pages(virt_to_page(addr), 1, !protect);
+	return true;
+}
+
+#endif /* _ASM_S390_KFENCE_H */