riscv: Move KASAN mapping next to the kernel mapping

Now that KASAN_SHADOW_OFFSET is defined at compile time as a config, this value must remain constant whatever the size of the virtual address space, which is only possible by pushing this region at the end of the address space next to the kernel mapping. Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
ammarfaizi2 · Jan 18, 2022 · 86168d52ec671f83f5b6e7f49adfd90ee2f12f23 · 86168d5
1 parent fa55b7d
commit 86168d52ec671f83f5b6e7f49adfd90ee2f12f23
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Showing 6 changed files with 32 additions and 25 deletions.
diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst
@@ -47,12 +47,12 @@ RISC-V Linux Kernel SV39
                                                               | Kernel-space virtual memory, shared between all processes:
   ____________________________________________________________|___________________________________________________________
                     |            |                  |         |
-   ffffffc000000000 | -256    GB | ffffffc7ffffffff |   32 GB | kasan
-   ffffffcefee00000 | -196    GB | ffffffcefeffffff |    2 MB | fixmap
-   ffffffceff000000 | -196    GB | ffffffceffffffff |   16 MB | PCI io
-   ffffffcf00000000 | -196    GB | ffffffcfffffffff |    4 GB | vmemmap
-   ffffffd000000000 | -192    GB | ffffffdfffffffff |   64 GB | vmalloc/ioremap space
-   ffffffe000000000 | -128    GB | ffffffff7fffffff |  124 GB | direct mapping of all physical memory
+   ffffffc6fee00000 | -228    GB | ffffffc6feffffff |    2 MB | fixmap
+   ffffffc6ff000000 | -228    GB | ffffffc6ffffffff |   16 MB | PCI io
+   ffffffc700000000 | -228    GB | ffffffc7ffffffff |    4 GB | vmemmap
+   ffffffc800000000 | -224    GB | ffffffd7ffffffff |   64 GB | vmalloc/ioremap space
+   ffffffd800000000 | -160    GB | fffffff6ffffffff |  124 GB | direct mapping of all physical memory
+   fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
   __________________|____________|__________________|_________|____________________________________________________________
                                                               |
                                                               |

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
@@ -161,12 +161,12 @@ config PAGE_OFFSET
 	default 0xC0000000 if 32BIT && MAXPHYSMEM_1GB
 	default 0x80000000 if 64BIT && !MMU
 	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
-	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
+	default 0xffffffd800000000 if 64BIT && MAXPHYSMEM_128GB
 
 config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN_GENERIC
-	default 0xdfffffc800000000 if 64BIT
+	default 0xdfffffff00000000 if 64BIT
 	default 0xffffffff if 32BIT
 
 config ARCH_FLATMEM_ENABLE

diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
@@ -28,8 +28,8 @@
 #define KASAN_SHADOW_SCALE_SHIFT	3
 
 #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_START	(KASAN_SHADOW_END - KASAN_SHADOW_SIZE)
+#define KASAN_SHADOW_END	MODULES_LOWEST_VADDR
 #define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
 
 void kasan_init(void);

diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
@@ -33,7 +33,11 @@
  */
 #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
 
-#define KERN_VIRT_SIZE (-PAGE_OFFSET)
+/*
+ * Half of the kernel address space (half of the entries of the page global
+ * directory) is for the direct mapping.
+ */
+#define KERN_VIRT_SIZE		((PTRS_PER_PGD / 2 * PGDIR_SIZE) / 2)
 
 #ifndef __ASSEMBLY__
 

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
@@ -39,8 +39,10 @@
 
 /* Modules always live before the kernel */
 #ifdef CONFIG_64BIT
-#define MODULES_VADDR	(PFN_ALIGN((unsigned long)&_end) - SZ_2G)
-#define MODULES_END	(PFN_ALIGN((unsigned long)&_start))
+/* This is used to define the end of the KASAN shadow region */
+#define MODULES_LOWEST_VADDR	(KERNEL_LINK_ADDR - SZ_2G)
+#define MODULES_VADDR		(PFN_ALIGN((unsigned long)&_end) - SZ_2G)
+#define MODULES_END		(PFN_ALIGN((unsigned long)&_start))
 #endif
 
 /*

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
@@ -103,6 +103,9 @@ static void __init print_vm_layout(void)
 	print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
 		  (unsigned long)high_memory);
 #ifdef CONFIG_64BIT
+#ifdef CONFIG_KASAN
+	print_mlm("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);
+#endif
 	print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
 		  (unsigned long)ADDRESS_SPACE_END);
 #endif
@@ -130,18 +133,8 @@ void __init mem_init(void)
 	print_vm_layout();
 }
 
-/*
- * The default maximal physical memory size is -PAGE_OFFSET for 32-bit kernel,
- * whereas for 64-bit kernel, the end of the virtual address space is occupied
- * by the modules/BPF/kernel mappings which reduces the available size of the
- * linear mapping.
- * Limit the memory size via mem.
- */
-#ifdef CONFIG_64BIT
-static phys_addr_t memory_limit = -PAGE_OFFSET - SZ_4G;
-#else
-static phys_addr_t memory_limit = -PAGE_OFFSET;
-#endif
+/* Limit the memory size via mem. */
+static phys_addr_t memory_limit;
 
 static int __init early_mem(char *p)
 {
@@ -612,6 +605,14 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 	riscv_pfn_base = PFN_DOWN(kernel_map.phys_addr);
 
+	/*
+	 * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit
+	 * kernel, whereas for 64-bit kernel, the end of the virtual address
+	 * space is occupied by the modules/BPF/kernel mappings which reduces
+	 * the available size of the linear mapping.
+	 */
+	memory_limit = KERN_VIRT_SIZE - (IS_ENABLED(CONFIG_64BIT) ? SZ_4G : 0);
+
 	/* Sanity check alignment and size */
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
 	BUG_ON((kernel_map.phys_addr % PMD_SIZE) != 0);