kasan: enable instrumentation of global variables

This feature let us to detect accesses out of bounds of global variables.
This will work as for globals in kernel image, so for globals in modules.
Currently this won't work for symbols in user-specified sections (e.g.
__init, __read_mostly, ...)

The idea of this is simple.  Compiler increases each global variable by
redzone size and add constructors invoking __asan_register_globals()
function.  Information about global variable (address, size, size with
redzone ...) passed to __asan_register_globals() so we could poison
variable's redzone.

This patch also forces module_alloc() to return 8*PAGE_SIZE aligned
address making shadow memory handling (
kasan_module_alloc()/kasan_module_free() ) more simple.  Such alignment
guarantees that each shadow page backing modules address space correspond
to only one module_alloc() allocation.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 99 insertions, 0 deletions

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 799c52b9826c..78fee632a7ee 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -22,6 +22,7 @@
 #include <linux/memblock.h>
 #include <linux/memory.h>
 #include <linux/mm.h>
+#include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -395,6 +396,57 @@ void kasan_kfree_large(const void *ptr)
 			KASAN_FREE_PAGE);
 }
 
+int kasan_module_alloc(void *addr, size_t size)
+{
+	void *ret;
+	size_t shadow_size;
+	unsigned long shadow_start;
+
+	shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
+	shadow_size = round_up(size >> KASAN_SHADOW_SCALE_SHIFT,
+			PAGE_SIZE);
+
+	if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
+		return -EINVAL;
+
+	ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
+			shadow_start + shadow_size,
+			GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
+			PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
+			__builtin_return_address(0));
+	return ret ? 0 : -ENOMEM;
+}
+
+void kasan_module_free(void *addr)
+{
+	vfree(kasan_mem_to_shadow(addr));
+}
+
+static void register_global(struct kasan_global *global)
+{
+	size_t aligned_size = round_up(global->size, KASAN_SHADOW_SCALE_SIZE);
+
+	kasan_unpoison_shadow(global->beg, global->size);
+
+	kasan_poison_shadow(global->beg + aligned_size,
+		global->size_with_redzone - aligned_size,
+		KASAN_GLOBAL_REDZONE);
+}
+
+void __asan_register_globals(struct kasan_global *globals, size_t size)
+{
+	int i;
+
+	for (i = 0; i < size; i++)
+		register_global(&globals[i]);
+}
+EXPORT_SYMBOL(__asan_register_globals);
+
+void __asan_unregister_globals(struct kasan_global *globals, size_t size)
+{
+}
+EXPORT_SYMBOL(__asan_unregister_globals);
+
 #define DEFINE_ASAN_LOAD_STORE(size)				\
 	void __asan_load##size(unsigned long addr)		\
 	{							\
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 1fcc1d81a9cf..4986b0acab21 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -11,6 +11,7 @@
 #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
 #define KASAN_KMALLOC_REDZONE   0xFC  /* redzone inside slub object */
 #define KASAN_KMALLOC_FREE      0xFB  /* object was freed (kmem_cache_free/kfree) */
+#define KASAN_GLOBAL_REDZONE    0xFA  /* redzone for global variable */
 
 /*
  * Stack redzone shadow values
@@ -21,6 +22,10 @@
 #define KASAN_STACK_RIGHT       0xF3
 #define KASAN_STACK_PARTIAL     0xF4
 
+/* Don't break randconfig/all*config builds */
+#ifndef KASAN_ABI_VERSION
+#define KASAN_ABI_VERSION 1
+#endif
 
 struct kasan_access_info {
 	const void *access_addr;
@@ -30,6 +35,26 @@ struct kasan_access_info {
 	unsigned long ip;
 };
 
+/* The layout of struct dictated by compiler */
+struct kasan_source_location {
+	const char *filename;
+	int line_no;
+	int column_no;
+};
+
+/* The layout of struct dictated by compiler */
+struct kasan_global {
+	const void *beg;		/* Address of the beginning of the global variable. */
+	size_t size;			/* Size of the global variable. */
+	size_t size_with_redzone;	/* Size of the variable + size of the red zone. 32 bytes aligned */
+	const void *name;
+	const void *module_name;	/* Name of the module where the global variable is declared. */
+	unsigned long has_dynamic_init;	/* This needed for C++ */
+#if KASAN_ABI_VERSION >= 4
+	struct kasan_source_location *location;
+#endif
+};
+
 void kasan_report_error(struct kasan_access_info *info);
 void kasan_report_user_access(struct kasan_access_info *info);
 
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 866732ef3db3..680ceedf810a 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -23,6 +23,8 @@
 #include <linux/types.h>
 #include <linux/kasan.h>
 
+#include <asm/sections.h>
+
 #include "kasan.h"
 #include "../slab.h"
 
@@ -61,6 +63,7 @@ static void print_error_description(struct kasan_access_info *info)
 		break;
 	case KASAN_PAGE_REDZONE:
 	case KASAN_KMALLOC_REDZONE:
+	case KASAN_GLOBAL_REDZONE:
 	case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
 		bug_type = "out of bounds access";
 		break;
@@ -80,6 +83,20 @@ static void print_error_description(struct kasan_access_info *info)
 		info->access_size, current->comm, task_pid_nr(current));
 }
 
+static inline bool kernel_or_module_addr(const void *addr)
+{
+	return (addr >= (void *)_stext && addr < (void *)_end)
+		|| (addr >= (void *)MODULES_VADDR
+			&& addr < (void *)MODULES_END);
+}
+
+static inline bool init_task_stack_addr(const void *addr)
+{
+	return addr >= (void *)&init_thread_union.stack &&
+		(addr <= (void *)&init_thread_union.stack +
+			sizeof(init_thread_union.stack));
+}
+
 static void print_address_description(struct kasan_access_info *info)
 {
 	const void *addr = info->access_addr;
@@ -107,6 +124,11 @@ static void print_address_description(struct kasan_access_info *info)
 		dump_page(page, "kasan: bad access detected");
 	}
 
+	if (kernel_or_module_addr(addr)) {
+		if (!init_task_stack_addr(addr))
+			pr_err("Address belongs to variable %pS\n", addr);
+	}
+
 	dump_stack();
 }