linux-kernel - [RFC PATCH V3 17/43] rv64ilp32_abi: riscv: Adapt kasan memory layout

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Message-Id: <20250325121624.523258-18-guoren@kernel.org>
Date: Tue, 25 Mar 2025 08:15:58 -0400
From: guoren@...nel.org
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Subject: [RFC PATCH V3 17/43] rv64ilp32_abi: riscv: Adapt kasan memory layout

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@...nel.org>

For generic KASAN, the size of each memory granule is 8, which
needs 1/8 address space. The kernel space is 2GiB in rv64ilp32,
so we need 256MiB range (0x80000000 ~ 0x90000000), and the offset
is 0x7000000 for the whole 4GiB address space.

 Virtual kernel memory layout:
       fixmap : 0x90a00000 - 0x90ffffff   (6144 kB)
       pci io : 0x91000000 - 0x91ffffff   (  16 MB)
      vmemmap : 0x92000000 - 0x93ffffff   (  32 MB)
      vmalloc : 0x94000000 - 0xb3ffffff   ( 512 MB)
      modules : 0xb4000000 - 0xb7ffffff   (  64 MB)
       lowmem : 0xc0000000 - 0xc7ffffff   ( 128 MB)
        kasan : 0x80000000 - 0x8fffffff   ( 256 MB) <=
       kernel : 0xb8000000 - 0xbfffffff   ( 128 MB)

Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@...nel.org>
---
 arch/riscv/include/asm/kasan.h | 6 +++++-
 arch/riscv/mm/kasan_init.c     | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
index e6a0071bdb56..dd3a211bc5d0 100644
--- a/arch/riscv/include/asm/kasan.h
+++ b/arch/riscv/include/asm/kasan.h
@@ -21,7 +21,7 @@
  * [KASAN_SHADOW_OFFSET, KASAN_SHADOW_END) cover all 64-bits of virtual
  * addresses. So KASAN_SHADOW_OFFSET should satisfy the following equation:
  *      KASAN_SHADOW_OFFSET = KASAN_SHADOW_END -
- *                              (1ULL << (64 - KASAN_SHADOW_SCALE_SHIFT))
+ *                              (1ULL << (BITS_PER_LONG - KASAN_SHADOW_SCALE_SHIFT))
  */
 #define KASAN_SHADOW_SCALE_SHIFT	3
 
@@ -31,7 +31,11 @@
  * aligned on PGDIR_SIZE, so force its alignment to ease its population.
  */
 #define KASAN_SHADOW_START	((KASAN_SHADOW_END - KASAN_SHADOW_SIZE) & PGDIR_MASK)
+#if defined(CONFIG_64BIT) && (BITS_PER_LONG == 32)
+#define KASAN_SHADOW_END	0x90000000UL
+#else
 #define KASAN_SHADOW_END	MODULES_LOWEST_VADDR
+#endif
 
 #ifdef CONFIG_KASAN
 #define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index 41c635d6aca4..1e864598779a 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -324,7 +324,7 @@ asmlinkage void __init kasan_early_init(void)
 	uintptr_t i;
 
 	BUILD_BUG_ON(KASAN_SHADOW_OFFSET !=
-		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
+		KASAN_SHADOW_END - (1UL << (BITS_PER_LONG - KASAN_SHADOW_SCALE_SHIFT)));
 
 	for (i = 0; i < PTRS_PER_PTE; ++i)
 		set_pte(kasan_early_shadow_pte + i,
-- 
2.40.1