powerpc/32: Add KASAN support

This patch adds KASAN support for PPC32. The following patch
will add an early activation of hash table for book3s. Until
then, a warning will be raised if trying to use KASAN on an
hash 6xx.

To support KASAN, this patch initialises that MMU mapings for
accessing to the KASAN shadow area defined in a previous patch.

An early mapping is set as soon as the kernel code has been
relocated at its definitive place.

Then the definitive mapping is set once paging is initialised.

For modules, the shadow area is allocated at module_alloc().

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/Makefile

@@ -26,3 +26,4 @@ obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
 obj-$(CONFIG_HIGHMEM)		+= highmem.o
 obj-$(CONFIG_PPC_COPRO_BASE)	+= copro_fault.o
 obj-$(CONFIG_PPC_PTDUMP)	+= ptdump/
+obj-$(CONFIG_KASAN)		+= kasan/

arch/powerpc/mm/init_32.c

@@ -46,6 +46,7 @@
 #include <asm/sections.h>
 #include <asm/hugetlb.h>
 #include <asm/kup.h>
+#include <asm/kasan.h>
 
 #include <mm/mmu_decl.h>
 
@@ -179,6 +180,8 @@ void __init MMU_init(void)
 	btext_unmap();
 #endif
 
+	kasan_mmu_init();
+
 	setup_kup();
 
 	/* Shortly after that, the entire linear mapping will be available */

arch/powerpc/mm/kasan/kasan_init_32.c

@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define DISABLE_BRANCH_PROFILING
+
+#include <linux/kasan.h>
+#include <linux/printk.h>
+#include <linux/memblock.h>
+#include <linux/sched/task.h>
+#include <linux/vmalloc.h>
+#include <asm/pgalloc.h>
+#include <asm/code-patching.h>
+#include <mm/mmu_decl.h>
+
+static void kasan_populate_pte(pte_t *ptep, pgprot_t prot)
+{
+	unsigned long va = (unsigned long)kasan_early_shadow_page;
+	phys_addr_t pa = __pa(kasan_early_shadow_page);
+	int i;
+
+	for (i = 0; i < PTRS_PER_PTE; i++, ptep++)
+		__set_pte_at(&init_mm, va, ptep, pfn_pte(PHYS_PFN(pa), prot), 0);
+}
+
+static int kasan_init_shadow_page_tables(unsigned long k_start, unsigned long k_end)
+{
+	pmd_t *pmd;
+	unsigned long k_cur, k_next;
+
+	pmd = pmd_offset(pud_offset(pgd_offset_k(k_start), k_start), k_start);
+
+	for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd++) {
+		pte_t *new;
+
+		k_next = pgd_addr_end(k_cur, k_end);
+		if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
+			continue;
+
+		new = pte_alloc_one_kernel(&init_mm);
+
+		if (!new)
+			return -ENOMEM;
+		kasan_populate_pte(new, PAGE_KERNEL_RO);
+		pmd_populate_kernel(&init_mm, pmd, new);
+	}
+	return 0;
+}
+
+static void __ref *kasan_get_one_page(void)
+{
+	if (slab_is_available())
+		return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+
+	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+}
+
+static int __ref kasan_init_region(void *start, size_t size)
+{
+	unsigned long k_start = (unsigned long)kasan_mem_to_shadow(start);
+	unsigned long k_end = (unsigned long)kasan_mem_to_shadow(start + size);
+	unsigned long k_cur;
+	int ret;
+	void *block = NULL;
+
+	ret = kasan_init_shadow_page_tables(k_start, k_end);
+	if (ret)
+		return ret;
+
+	if (!slab_is_available())
+		block = memblock_alloc(k_end - k_start, PAGE_SIZE);
+
+	for (k_cur = k_start; k_cur < k_end; k_cur += PAGE_SIZE) {
+		pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(k_cur), k_cur), k_cur);
+		void *va = block ? block + k_cur - k_start : kasan_get_one_page();
+		pte_t pte = pfn_pte(PHYS_PFN(__pa(va)), PAGE_KERNEL);
+
+		if (!va)
+			return -ENOMEM;
+
+		__set_pte_at(&init_mm, k_cur, pte_offset_kernel(pmd, k_cur), pte, 0);
+	}
+	flush_tlb_kernel_range(k_start, k_end);
+	return 0;
+}
+
+static void __init kasan_remap_early_shadow_ro(void)
+{
+	kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL_RO);
+
+	flush_tlb_kernel_range(KASAN_SHADOW_START, KASAN_SHADOW_END);
+}
+
+void __init kasan_mmu_init(void)
+{
+	int ret;
+	struct memblock_region *reg;
+
+	for_each_memblock(memory, reg) {
+		phys_addr_t base = reg->base;
+		phys_addr_t top = min(base + reg->size, total_lowmem);
+
+		if (base >= top)
+			continue;
+
+		ret = kasan_init_region(__va(base), top - base);
+		if (ret)
+			panic("kasan: kasan_init_region() failed");
+	}
+}
+
+void __init kasan_init(void)
+{
+	kasan_remap_early_shadow_ro();
+
+	clear_page(kasan_early_shadow_page);
+
+	/* At this point kasan is fully initialized. Enable error messages */
+	init_task.kasan_depth = 0;
+	pr_info("KASAN init done\n");
+}
+
+#ifdef CONFIG_MODULES
+void *module_alloc(unsigned long size)
+{
+	void *base = vmalloc_exec(size);
+
+	if (!base)
+		return NULL;
+
+	if (!kasan_init_region(base, size))
+		return base;
+
+	vfree(base);
+
+	return NULL;
+}
+#endif
+
+void __init kasan_early_init(void)
+{
+	unsigned long addr = KASAN_SHADOW_START;
+	unsigned long end = KASAN_SHADOW_END;
+	unsigned long next;
+	pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(addr), addr), addr);
+
+	BUILD_BUG_ON(KASAN_SHADOW_START & ~PGDIR_MASK);
+
+	kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL);
+
+	do {
+		next = pgd_addr_end(addr, end);
+		pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
+	} while (pmd++, addr = next, addr != end);
+
+	if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		WARN(true, "KASAN not supported on hash 6xx");
+}