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>

5 files changed, 32 insertions, 25 deletions

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7a68a4106e5a..7f8aea333291 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -160,12 +160,12 @@ config PAGE_OFFSET
 	hex
 	default 0xC0000000 if 32BIT
 	default 0x80000000 if 64BIT && !MMU
-	default 0xffffffe000000000 if 64BIT
+	default 0xffffffd800000000 if 64BIT
 
 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
index b00f503ec124..257a2495145a 100644
--- 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
index b3e5ff0125fe..a18c989e600c 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -33,8 +33,6 @@
  */
 #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
 
-#define KERN_VIRT_SIZE (-PAGE_OFFSET)
-
 #ifndef __ASSEMBLY__
 
 #define clear_page(pgaddr)			memset((pgaddr), 0, PAGE_SIZE)
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index bf204e7c1f74..fa400b2abb36 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -24,6 +24,17 @@
 #define KERNEL_LINK_ADDR	PAGE_OFFSET
 #endif
 
+/* Number of entries in the page global directory */
+#define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
+/* Number of entries in the page table */
+#define PTRS_PER_PTE    (PAGE_SIZE / sizeof(pte_t))
+
+/*
+ * 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)
+
 #define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
 #define VMALLOC_END      (PAGE_OFFSET - 1)
 #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
@@ -39,8 +50,10 @@
 
 /* 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
 
 /*
@@ -108,11 +121,6 @@
 #endif /* CONFIG_XIP_KERNEL */
 
 #ifdef CONFIG_MMU
-/* Number of entries in the page global directory */
-#define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
-/* Number of entries in the page table */
-#define PTRS_PER_PTE    (PAGE_SIZE / sizeof(pte_t))
-
 /* Number of PGD entries that a user-mode program can use */
 #define USER_PTRS_PER_PGD   (TASK_SIZE / PGDIR_SIZE)
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 24b2b8044602..f515964e9c00 100644
--- 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);