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>

arch/s390/Kconfig

@@ -138,6 +138,7 @@ config S390
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN
 	select HAVE_ARCH_KASAN_VMALLOC
+	select HAVE_ARCH_KFENCE
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_SOFT_DIRTY

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 */

arch/s390/mm/fault.c

@@ -31,6 +31,7 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/hugetlb.h>
+#include <linux/kfence.h>
 #include <asm/asm-offsets.h>
 #include <asm/diag.h>
 #include <asm/gmap.h>
@@ -356,6 +357,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	unsigned long address;
 	unsigned int flags;
 	vm_fault_t fault;
+	bool is_write;
 
 	tsk = current;
 	/*
@@ -369,6 +371,8 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 
 	mm = tsk->mm;
 	trans_exc_code = regs->int_parm_long;
+	address = trans_exc_code & __FAIL_ADDR_MASK;
+	is_write = (trans_exc_code & store_indication) == 0x400;
 
 	/*
 	 * Verify that the fault happened in user space, that
@@ -379,6 +383,8 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	type = get_fault_type(regs);
 	switch (type) {
 	case KERNEL_FAULT:
+		if (kfence_handle_page_fault(address, is_write, regs))
+			return 0;
 		goto out;
 	case USER_FAULT:
 	case GMAP_FAULT:
@@ -387,12 +393,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 		break;
 	}
 
-	address = trans_exc_code & __FAIL_ADDR_MASK;
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
 	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
-	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
+	if (access == VM_WRITE || is_write)
 		flags |= FAULT_FLAG_WRITE;
 	mmap_read_lock(mm);
 

arch/s390/mm/init.c

@@ -34,6 +34,7 @@
 #include <asm/processor.h>
 #include <linux/uaccess.h>
 #include <asm/pgalloc.h>
+#include <asm/kfence.h>
 #include <asm/ptdump.h>
 #include <asm/dma.h>
 #include <asm/lowcore.h>
@@ -200,7 +201,7 @@ void __init mem_init(void)
         high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
 
 	pv_init();
-
+	kfence_split_mapping();
 	/* Setup guest page hinting */
 	cmma_init();
 

arch/s390/mm/pageattr.c

@@ -8,6 +8,7 @@
 #include <asm/cacheflush.h>
 #include <asm/facility.h>
 #include <asm/pgalloc.h>
+#include <asm/kfence.h>
 #include <asm/page.h>
 #include <asm/set_memory.h>
 
@@ -326,7 +327,7 @@ int __set_memory(unsigned long addr, int numpages, unsigned long flags)
 	return change_page_attr(addr, addr + numpages * PAGE_SIZE, flags);
 }
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
+#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KFENCE)
 
 static void ipte_range(pte_t *pte, unsigned long address, int nr)
 {