[PATCH 5.10 76/77] riscv: Fix asan-stack clang build

[Greg Kroah-Hartman]

From: Alexandre Ghiti <alexandre.ghiti@xxxxxxxxxxxxx>

commit 54c5639d8f507ebefa814f574cb6f763033a72a5 upstream.

Nathan reported that because KASAN_SHADOW_OFFSET was not defined in
Kconfig, it prevents asan-stack from getting disabled with clang even
when CONFIG_KASAN_STACK is disabled: fix this by defining the
corresponding config.

Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Alexandre Ghiti <alexandre.ghiti@xxxxxxxxxxxxx>
Fixes: 8ad8b72721d0 ("riscv: Add KASAN support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/riscv/Kconfig             |    6 ++++++
 arch/riscv/include/asm/kasan.h |    3 +--
 arch/riscv/mm/kasan_init.c     |    3 +++
 3 files changed, 10 insertions(+), 2 deletions(-)

--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -138,6 +138,12 @@ config PAGE_OFFSET
 	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
 	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
 
+config KASAN_SHADOW_OFFSET
+	hex
+	depends on KASAN_GENERIC
+	default 0xdfffffc800000000 if 64BIT
+	default 0xffffffff if 32BIT
+
 config ARCH_FLATMEM_ENABLE
 	def_bool y
 
--- a/arch/riscv/include/asm/kasan.h
+++ b/arch/riscv/include/asm/kasan.h
@@ -14,8 +14,7 @@
 #define KASAN_SHADOW_START	KERN_VIRT_START /* 2^64 - 2^38 */
 #define KASAN_SHADOW_END	(KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
 
-#define KASAN_SHADOW_OFFSET	(KASAN_SHADOW_END - (1ULL << \
-					(64 - KASAN_SHADOW_SCALE_SHIFT)))
+#define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
 
 void kasan_init(void);
 asmlinkage void kasan_early_init(void);
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -16,6 +16,9 @@ asmlinkage void __init kasan_early_init(
 	uintptr_t i;
 	pgd_t *pgd = early_pg_dir + pgd_index(KASAN_SHADOW_START);
 
+	BUILD_BUG_ON(KASAN_SHADOW_OFFSET !=
+		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
+
 	for (i = 0; i < PTRS_PER_PTE; ++i)
 		set_pte(kasan_early_shadow_pte + i,
 			mk_pte(virt_to_page(kasan_early_shadow_page),