[PATCH v3 1/5] mm: kasan: introduce generic kasan_populate_zero_shadow()

[Andrey Ryabinin <a.ryabinin@samsung.com>]

Introduce generic kasan_populate_zero_shadow(start, end).
This function maps kasan_zero_page to the [start, end] addresses.

In follow on patches it will be used for ARMv8 (and maybe other
architectures) and will replace x86_64 specific populate_zero_shadow().

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
---
 arch/x86/mm/kasan_init_64.c |   8 +--
 include/linux/kasan.h       |   8 +++
 mm/kasan/Makefile           |   2 +-
 mm/kasan/kasan_init.c       | 142 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 155 insertions(+), 5 deletions(-)
 create mode 100644 mm/kasan/kasan_init.c

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index e1840f3..2390dba 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -12,9 +12,9 @@
 extern pgd_t early_level4_pgt[PTRS_PER_PGD];
 extern struct range pfn_mapped[E820_X_MAX];
 
-static pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_bss;
-static pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_bss;
-static pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss;
+pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_bss;
+pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_bss;
+pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss;
 
 /*
  * This page used as early shadow. We don't use empty_zero_page
@@ -24,7 +24,7 @@ static pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss;
  * that allowed to access, but not instrumented by kasan
  * (vmalloc/vmemmap ...).
  */
-static unsigned char kasan_zero_page[PAGE_SIZE] __page_aligned_bss;
+unsigned char kasan_zero_page[PAGE_SIZE] __page_aligned_bss;
 
 static int __init map_range(struct range *range)
 {
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 5486d77..5ef3925 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -13,8 +13,16 @@ struct vm_struct;
 #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
 
 #include <asm/kasan.h>
+#include <asm/pgtable.h>
 #include <linux/sched.h>
 
+extern unsigned char kasan_zero_page[PAGE_SIZE];
+extern pte_t kasan_zero_pte[PTRS_PER_PTE];
+extern pmd_t kasan_zero_pmd[PTRS_PER_PMD];
+extern pud_t kasan_zero_pud[PTRS_PER_PUD];
+
+void kasan_populate_zero_shadow(const void *start, const void *end);
+
 static inline void *kasan_mem_to_shadow(const void *addr)
 {
 	return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index bd837b8..6471014 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -5,4 +5,4 @@ CFLAGS_REMOVE_kasan.o = -pg
 # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
 CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
-obj-y := kasan.o report.o
+obj-y := kasan.o report.o kasan_init.o
diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
new file mode 100644
index 0000000..37fb46a
--- /dev/null
+++ b/mm/kasan/kasan_init.c
@@ -0,0 +1,142 @@
+#include <linux/bootmem.h>
+#include <linux/init.h>
+#include <linux/kasan.h>
+#include <linux/kernel.h>
+#include <linux/memblock.h>
+#include <linux/pfn.h>
+
+#include <asm/page.h>
+#include <asm/pgalloc.h>
+
+static __init void *early_alloc(size_t size, int node)
+{
+	return memblock_virt_alloc_try_nid(size, size, __pa(MAX_DMA_ADDRESS),
+					BOOTMEM_ALLOC_ACCESSIBLE, node);
+}
+
+static int __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
+				unsigned long end)
+{
+	pte_t *pte = pte_offset_kernel(pmd, addr);
+	pte_t zero_pte;
+
+	zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
+	zero_pte = pte_wrprotect(zero_pte);
+
+	while (addr + PAGE_SIZE <= end) {
+		set_pte_at(&init_mm, addr, pte, zero_pte);
+		addr += PAGE_SIZE;
+		pte = pte_offset_kernel(pmd, addr);
+	}
+	return 0;
+}
+
+static int __init zero_pmd_populate(pud_t *pud, unsigned long addr,
+				unsigned long end)
+{
+	int ret = 0;
+	pmd_t *pmd = pmd_offset(pud, addr);
+	unsigned long next;
+
+	do {
+		next = pmd_addr_end(addr, end);
+
+		if (IS_ALIGNED(addr, PMD_SIZE) && end - addr >= PMD_SIZE) {
+			pmd_populate_kernel(&init_mm, pmd, kasan_zero_pte);
+			continue;
+		}
+
+		if (pmd_none(*pmd)) {
+			void *p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
+			if (!p)
+				return -ENOMEM;
+			pmd_populate_kernel(&init_mm, pmd, p);
+		}
+		zero_pte_populate(pmd, addr, pmd_addr_end(addr, end));
+	} while (pmd++, addr = next, addr != end);
+
+	return ret;
+}
+
+static int __init zero_pud_populate(pgd_t *pgd, unsigned long addr,
+				unsigned long end)
+{
+	int ret = 0;
+	pud_t *pud = pud_offset(pgd, addr);
+	unsigned long next;
+
+	do {
+		next = pud_addr_end(addr, end);
+		if (IS_ALIGNED(addr, PUD_SIZE) && end - addr >= PUD_SIZE) {
+			pmd_t *pmd;
+
+			pud_populate(&init_mm, pud, kasan_zero_pmd);
+			pmd = pmd_offset(pud, addr);
+			pmd_populate_kernel(&init_mm, pmd, kasan_zero_pte);
+			continue;
+		}
+
+		if (pud_none(*pud)) {
+			void *p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
+			if (!p)
+				return -ENOMEM;
+			pud_populate(&init_mm, pud, p);
+		}
+		zero_pmd_populate(pud, addr, pud_addr_end(addr, end));
+	} while (pud++, addr = next, addr != end);
+
+	return ret;
+}
+
+static int __init zero_pgd_populate(unsigned long addr, unsigned long end)
+{
+	int ret = 0;
+	pgd_t *pgd = pgd_offset_k(addr);
+	unsigned long next;
+
+	do {
+		next = pgd_addr_end(addr, end);
+
+		if (IS_ALIGNED(addr, PGDIR_SIZE) && end - addr >= PGDIR_SIZE) {
+			pud_t *pud;
+			pmd_t *pmd;
+
+			/*
+			 * kasan_zero_pud should be populated with pmds
+			 * at this moment.
+			 * [pud,pmd]_populate*() bellow needed only for
+			 * 3,2 - level page tables where we don't have
+			 * puds,pmds, so pgd_populate(), pud_populate()
+			 * is noops.
+			 */
+			pgd_populate(&init_mm, pgd, kasan_zero_pud);
+			pud = pud_offset(pgd, addr);
+			pud_populate(&init_mm, pud, kasan_zero_pmd);
+			pmd = pmd_offset(pud, addr);
+			pmd_populate_kernel(&init_mm, pmd, kasan_zero_pte);
+			continue;
+		}
+
+		if (pgd_none(*pgd)) {
+			void *p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
+			if (!p)
+				return -ENOMEM;
+			pgd_populate(&init_mm, pgd, p);
+		}
+		zero_pud_populate(pgd, addr, next);
+	} while (pgd++, addr = next, addr != end);
+
+	return ret;
+}
+
+/**
+ * kasan_populate_zero_shadow - populate shadow memory region with
+ *                               kasan_zero_page
+ * @start - start of the memory range to populate
+ * @end   - end of the memory range to populate
+ */
+void __init kasan_populate_zero_shadow(const void *start, const void *end)
+{
+	if (zero_pgd_populate((unsigned long)start, (unsigned long)end))
+		panic("kasan: unable to map zero shadow!");
+}
-- 
2.4.5