[PATCH v6 6/6] powerpc/32: enable CONFIG_KASAN for book3s hash

[Christophe Leroy <christophe.leroy@c-s.fr>]

The challenge with book3s/32 is that the hash table management
has to be set up before being able to use KASAN.

This patch adds a kasan_arch_is_ready() helper to defer
the activation of KASAN until paging is ready.

This limits KASAN to KASAN_MINIMAL mode. The downside of it
is that the 603, which doesn't use hash table, also gets
downgraded to KASAN_MINIMAL because this is no way to
activate full support dynamically because that's compiled-in.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/Makefile                 |  2 ++
 arch/powerpc/include/asm/kasan.h      | 13 +++++++++++++
 arch/powerpc/mm/kasan/kasan_init_32.c | 27 +++++++++++++++++++++++++--
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index f0738099e31e..06d085558d21 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -428,11 +428,13 @@ endif
 endif
 
 ifdef CONFIG_KASAN
+ifndef CONFIG_PPC_BOOK3S_32
 prepare: kasan_prepare
 
 kasan_prepare: prepare0
        $(eval KASAN_SHADOW_OFFSET = $(shell awk '{if ($$2 == "KASAN_SHADOW_OFFSET") print $$3;}' include/generated/asm-offsets.h))
 endif
+endif
 
 # Check toolchain versions:
 # - gcc-4.6 is the minimum kernel-wide version so nothing required.
diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index 0bc9148f5d87..97b5ccf0702f 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -16,6 +16,7 @@
 
 #include <asm/page.h>
 #include <asm/pgtable-types.h>
+#include <linux/jump_label.h>
 
 #define KASAN_SHADOW_SCALE_SHIFT	3
 
@@ -34,5 +35,17 @@
 void kasan_early_init(void);
 void kasan_init(void);
 
+extern struct static_key_false powerpc_kasan_enabled_key;
+
+static inline bool kasan_arch_is_ready(void)
+{
+	if (!IS_ENABLED(CONFIG_BOOK3S_32))
+		return true;
+	if (static_branch_likely(&powerpc_kasan_enabled_key))
+		return true;
+	return false;
+}
+#define kasan_arch_is_ready kasan_arch_is_ready
+
 #endif /* __ASSEMBLY */
 #endif
diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
index 495c908d6ee6..f24f8f56d450 100644
--- a/arch/powerpc/mm/kasan/kasan_init_32.c
+++ b/arch/powerpc/mm/kasan/kasan_init_32.c
@@ -9,6 +9,9 @@
 #include <linux/vmalloc.h>
 #include <asm/pgalloc.h>
 
+/* Used by BOOK3S_32 only */
+DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
+
 void __init kasan_early_init(void)
 {
 	unsigned long addr = KASAN_SHADOW_START;
@@ -21,7 +24,7 @@ void __init kasan_early_init(void)
 	BUILD_BUG_ON(KASAN_SHADOW_START & ~PGDIR_MASK);
 
 	if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
-		panic("KASAN not supported with Hash MMU\n");
+		return;
 
 	for (i = 0; i < PTRS_PER_PTE; i++)
 		__set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page,
@@ -32,6 +35,22 @@ void __init kasan_early_init(void)
 		next = pgd_addr_end(addr, end);
 		pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
 	} while (pmd++, addr = next, addr != end);
+
+	if (IS_ENABLED(CONFIG_PPC_BOOK3S_32)) {
+		jump_label_init();
+		static_branch_enable(&powerpc_kasan_enabled_key);
+	}
+}
+
+static void __init kasan_late_init(void)
+{
+	unsigned long addr;
+	phys_addr_t pa = __pa(kasan_early_shadow_page);
+
+	for (addr = KASAN_SHADOW_START; addr < KASAN_SHADOW_END; addr += PAGE_SIZE)
+		map_kernel_page(addr, pa, PAGE_KERNEL_RO);
+
+	static_branch_enable(&powerpc_kasan_enabled_key);
 }
 
 static void __ref *kasan_get_one_page(void)
@@ -113,6 +132,9 @@ void __init kasan_init(void)
 {
 	struct memblock_region *reg;
 
+	if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		kasan_late_init();
+
 	for_each_memblock(memory, reg) {
 		int ret = kasan_init_region(__va(reg->base), reg->size);
 
@@ -120,7 +142,8 @@ void __init kasan_init(void)
 			panic("kasan: kasan_init_region() failed");
 	}
 
-	kasan_remap_early_shadow_ro();
+	if (!early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		kasan_remap_early_shadow_ro();
 
 	clear_page(kasan_early_shadow_page);
 
-- 
2.13.3