new file mode 100644
@@ -0,0 +1,27 @@
+#!/bin/sh
+
+# Print out the KASAN_SHADOW_OFFSETS required to place the KASAN SHADOW
+# start address at the mid-point of the kernel VA space
+
+print_kasan_offset () {
+ printf "%02d\t" $1
+ printf "0x%08x00000000\n" $(( (0xffffffff & (-1 << ($1 - 1 - 32))) \
+ + (1 << ($1 - 32 - $2)) \
+ - (1 << (64 - 32 - $2)) ))
+}
+
+echo KASAN_SHADOW_SCALE_SHIFT = 3
+printf "VABITS\tKASAN_SHADOW_OFFSET\n"
+print_kasan_offset 48 3
+print_kasan_offset 47 3
+print_kasan_offset 42 3
+print_kasan_offset 39 3
+print_kasan_offset 36 3
+echo
+echo KASAN_SHADOW_SCALE_SHIFT = 4
+printf "VABITS\tKASAN_SHADOW_OFFSET\n"
+print_kasan_offset 48 4
+print_kasan_offset 47 4
+print_kasan_offset 42 4
+print_kasan_offset 39 4
+print_kasan_offset 36 4
@@ -297,6 +297,21 @@ config ARCH_SUPPORTS_UPROBES
config ARCH_PROC_KCORE_TEXT
def_bool y
+config KASAN_SHADOW_OFFSET
+ hex
+ depends on KASAN
+ default 0xdfffa00000000000 if (ARM64_VA_BITS_48 || ARM64_USER_VA_BITS_52) && !KASAN_SW_TAGS
+ default 0xdfffd00000000000 if ARM64_VA_BITS_47 && !KASAN_SW_TAGS
+ default 0xdffffe8000000000 if ARM64_VA_BITS_42 && !KASAN_SW_TAGS
+ default 0xdfffffd000000000 if ARM64_VA_BITS_39 && !KASAN_SW_TAGS
+ default 0xdffffffa00000000 if ARM64_VA_BITS_36 && !KASAN_SW_TAGS
+ default 0xefff900000000000 if (ARM64_VA_BITS_48 || ARM64_USER_VA_BITS_52) && KASAN_SW_TAGS
+ default 0xefffc80000000000 if ARM64_VA_BITS_47 && KASAN_SW_TAGS
+ default 0xeffffe4000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS
+ default 0xefffffc800000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS
+ default 0xeffffff900000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
+ default 0xffffffffffffffff
+
source "arch/arm64/Kconfig.platforms"
menu "Kernel Features"
@@ -126,14 +126,6 @@ KBUILD_CFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
KBUILD_CPPFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
KBUILD_AFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
-# KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
-# - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
-# in 32-bit arithmetic
-KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
- (0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 1 - 32))) \
- + (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
- - (1 << (64 - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) )) )
-
export TEXT_OFFSET GZFLAGS
core-y += arch/arm64/kernel/ arch/arm64/mm/
@@ -18,11 +18,8 @@
* KASAN_SHADOW_START: beginning of the kernel virtual addresses.
* KASAN_SHADOW_END: KASAN_SHADOW_START + 1/N of kernel virtual addresses,
* where N = (1 << KASAN_SHADOW_SCALE_SHIFT).
- */
-#define KASAN_SHADOW_START (VA_START)
-#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
-
-/*
+ *
+ * KASAN_SHADOW_OFFSET:
* This value is used to map an address to the corresponding shadow
* address by the following formula:
* shadow_addr = (address >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET
@@ -33,8 +30,8 @@
* KASAN_SHADOW_OFFSET = KASAN_SHADOW_END -
* (1ULL << (64 - KASAN_SHADOW_SCALE_SHIFT))
*/
-#define KASAN_SHADOW_OFFSET (KASAN_SHADOW_END - (1ULL << \
- (64 - KASAN_SHADOW_SCALE_SHIFT)))
+#define _KASAN_SHADOW_START(va) (KASAN_SHADOW_END - (1UL << ((va) - KASAN_SHADOW_SCALE_SHIFT)))
+#define KASAN_SHADOW_START _KASAN_SHADOW_START(VA_BITS)
void kasan_init(void);
void kasan_copy_shadow(pgd_t *pgdir);
@@ -42,7 +42,7 @@
#define PAGE_OFFSET (UL(0xffffffffffffffff) - \
(UL(1) << VA_BITS) + 1)
#define KIMAGE_VADDR (MODULES_END)
-#define BPF_JIT_REGION_START (VA_START + KASAN_SHADOW_SIZE)
+#define BPF_JIT_REGION_START (KASAN_SHADOW_END)
#define BPF_JIT_REGION_SIZE (SZ_128M)
#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
@@ -68,11 +68,13 @@
* significantly, so double the (minimum) stack size when they are in use.
*/
#ifdef CONFIG_KASAN
-#define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
+#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
+#define KASAN_SHADOW_END ((UL(1) << (64 - KASAN_SHADOW_SCALE_SHIFT)) \
+ + KASAN_SHADOW_OFFSET)
#define KASAN_THREAD_SHIFT 1
#else
-#define KASAN_SHADOW_SIZE (0)
#define KASAN_THREAD_SHIFT 0
+#define KASAN_SHADOW_END (VA_START)
#endif
#define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT)
KASAN_SHADOW_OFFSET is a constant that is supplied to gcc as a command line argument and affects the codegen of the inline address sanetiser. Essentially, for an example memory access: *ptr1 = val; The compiler will insert logic similar to the below: shadowValue = *(ptr1 >> KASAN_SHADOW_SCALE_SHIFT + KASAN_SHADOW_OFFSET) if (somethingWrong(shadowValue)) flagAnError(); This code sequence is inserted into many places, thus KASAN_SHADOW_OFFSET is essentially baked into many places in the kernel text. If we want to run a single kernel binary with multiple address spaces, then we need to do this with KASAN_SHADOW_OFFSET fixed. Thankfully, due to the way the KASAN_SHADOW_OFFSET is used to provide shadow addresses we know that the end of the shadow region is constant w.r.t. VA space size: KASAN_SHADOW_END = ~0 >> KASAN_SHADOW_SCALE_SHIFT + KASAN_SHADOW_OFFSET This means that if we increase the size of the VA space, the start of the KASAN region expands into lower addresses whilst the end of the KASAN region is fixed. Currently the arm64 code computes KASAN_SHADOW_OFFSET at build time via build scripts with the VA size used as a parameter. (There are build time checks in the C code too to ensure that expected values are being derived). It is sufficient, and indeed is a simplification, to remove the build scripts (and build time checks) entirely and instead provide KASAN_SHADOW_OFFSET values. This patch removes the logic to compute the KASAN_SHADOW_OFFSET in the arm64 Makefile, and instead we adopt the approach used by x86 to supply offset values in kConfig. To help debug/develop future VA space changes, the Makefile logic has been preserved in a script file in the arm64 Documentation folder. Signed-off-by: Steve Capper <steve.capper@arm.com> --- Changed in V5, preserved a BUILD_BUG_ON that was removed before Removed spurious KASAN_EXTRA logic --- Documentation/arm64/kasan-offsets.sh | 27 +++++++++++++++++++++++++++ arch/arm64/Kconfig | 15 +++++++++++++++ arch/arm64/Makefile | 8 -------- arch/arm64/include/asm/kasan.h | 11 ++++------- arch/arm64/include/asm/memory.h | 8 +++++--- 5 files changed, 51 insertions(+), 18 deletions(-) create mode 100644 Documentation/arm64/kasan-offsets.sh