Re: [PATCH 1/2] riscv: Fix asan-stack clang build

From: Palmer Dabbelt
Date: Wed Oct 27 2021 - 19:06:28 EST


On Tue, 26 Oct 2021 21:58:42 PDT (-0700), alexandre.ghiti@xxxxxxxxxxxxx wrote:
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>
---
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(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c1abbc876e5b..79250b1ed54e 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -162,6 +162,12 @@ 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

I thought I posted this somewhere, but this is exactly what my first guess was. The problem is that it's hanging on boot for me. I don't really have anything exotic going on, it's just a defconfig with CONFIG_KASAN=y running in QEMU.

Does this boot for you?

+
config ARCH_FLATMEM_ENABLE
def_bool !NUMA

diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
index a2b3d9cdbc86..b00f503ec124 100644
--- a/arch/riscv/include/asm/kasan.h
+++ b/arch/riscv/include/asm/kasan.h
@@ -30,8 +30,7 @@
#define KASAN_SHADOW_SIZE (UL(1) << ((CONFIG_VA_BITS - 1) - KASAN_SHADOW_SCALE_SHIFT))
#define KASAN_SHADOW_START KERN_VIRT_START
#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);
diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index d7189c8714a9..8175e98b9073 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -17,6 +17,9 @@ asmlinkage void __init kasan_early_init(void)
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),