[PATCH v4 03/11] arm64, kfence: enable KFENCE for ARM64

Marco Elver
2020-09-29T13:41:17Z

Add architecture specific implementation details for KFENCE and enable
KFENCE for the arm64 architecture. In particular, this implements the
required interface in <asm/kfence.h>. Currently, the arm64 version does
not yet use a statically allocated memory pool, at the cost of a pointer
load for each is_kfence_address().

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Co-developed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Marco Elver <elver@google.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/kfence.h | 39 +++++++++++++++++++++++++++++++++
arch/arm64/mm/fault.c | 4 ++++
3 files changed, 44 insertions(+)
create mode 100644 arch/arm64/include/asm/kfence.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6d232837cbee..1acc6b2877c3 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -132,6 +132,7 @@ config ARM64
select HAVE_ARCH_JUMP_LABEL_RELATIVE
select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN
+ select HAVE_ARCH_KFENCE if (!ARM64_16K_PAGES && !ARM64_64K_PAGES)
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
new file mode 100644
index 000000000000..608dde80e5ca
--- /dev/null
+++ b/arch/arm64/include/asm/kfence.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_KFENCE_H
+#define __ASM_KFENCE_H
+
+#include <linux/kfence.h>
+#include <linux/log2.h>
+#include <linux/mm.h>
+
+#include <asm/cacheflush.h>
+
+#define KFENCE_SKIP_ARCH_FAULT_HANDLER "el1_sync"
+
+/*
+ * FIXME: Support HAVE_ARCH_KFENCE_STATIC_POOL: Use the statically allocated
+ * __kfence_pool, to avoid the extra pointer load for is_kfence_address(). By
+ * default, however, we do not have struct pages for static allocations.
+ */
+
+static inline bool arch_kfence_initialize_pool(void)
+{
+ const unsigned int num_pages = ilog2(roundup_pow_of_two(KFENCE_POOL_SIZE / PAGE_SIZE));
+ struct page *pages = alloc_pages(GFP_KERNEL, num_pages);
+
+ if (!pages)
+ return false;
+
+ __kfence_pool = page_address(pages);
+ return true;
+}
+
+static inline bool kfence_protect_page(unsigned long addr, bool protect)
+{
+ set_memory_valid(addr, 1, !protect);
+
+ return true;
+}
+
+#endif /* __ASM_KFENCE_H */
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f07333e86c2f..d5b72ecbeeea 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -10,6 +10,7 @@
#include <linux/acpi.h>
#include <linux/bitfield.h>
#include <linux/extable.h>
+#include <linux/kfence.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
@@ -310,6 +311,9 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
"Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
return;

+ if (kfence_handle_page_fault(addr))
+ return;
+
if (is_el1_permission_fault(addr, esr, regs)) {
if (esr & ESR_ELx_WNR)
msg = "write to read-only memory";
--
2.28.0.709.gb0816b6eb0-goog