kasan: add kernel address sanitizer infrastructure

Kernel Address sanitizer (KASan) is a dynamic memory error detector.  It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.

KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required.  v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.

This patch only adds infrastructure for kernel address sanitizer.  It's
not available for use yet.  The idea and some code was borrowed from [1].

Basic idea:

The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.

Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.

Here is function to translate address to corresponding shadow address:

     unsigned long kasan_mem_to_shadow(unsigned long addr)
     {
                return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
     }

where KASAN_SHADOW_SCALE_SHIFT = 3.

So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible.  Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).

To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.

These functions check whether memory region is valid to access or not by
checking corresponding shadow memory.  If access is not valid an error
printed.

Historical background of the address sanitizer from Dmitry Vyukov:

	"We've developed the set of tools, AddressSanitizer (Asan),
	ThreadSanitizer and MemorySanitizer, for user space. We actively use
	them for testing inside of Google (continuous testing, fuzzing,
	running prod services). To date the tools have found more than 10'000
	scary bugs in Chromium, Google internal codebase and various
	open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
	lots of others): [2] [3] [4].
	The tools are part of both gcc and clang compilers.

	We have not yet done massive testing under the Kernel AddressSanitizer
	(it's kind of chicken and egg problem, you need it to be upstream to
	start applying it extensively). To date it has found about 50 bugs.
	Bugs that we've found in upstream kernel are listed in [5].
	We've also found ~20 bugs in out internal version of the kernel. Also
	people from Samsung and Oracle have found some.

	[...]

	As others noted, the main feature of AddressSanitizer is its
	performance due to inline compiler instrumentation and simple linear
	shadow memory. User-space Asan has ~2x slowdown on computational
	programs and ~2x memory consumption increase. Taking into account that
	kernel usually consumes only small fraction of CPU and memory when
	running real user-space programs, I would expect that kernel Asan will
	have ~10-30% slowdown and similar memory consumption increase (when we
	finish all tuning).

	I agree that Asan can well replace kmemcheck. We have plans to start
	working on Kernel MemorySanitizer that finds uses of unitialized
	memory. Asan+Msan will provide feature-parity with kmemcheck. As
	others noted, Asan will unlikely replace debug slab and pagealloc that
	can be enabled at runtime. Asan uses compiler instrumentation, so even
	if it is disabled, it still incurs visible overheads.

	Asan technology is easily portable to other architectures. Compiler
	instrumentation is fully portable. Runtime has some arch-dependent
	parts like shadow mapping and atomic operation interception. They are
	relatively easy to port."

Comparison with other debugging features:
========================================

KMEMCHECK:

  - KASan can do almost everything that kmemcheck can.  KASan uses
    compile-time instrumentation, which makes it significantly faster than
    kmemcheck.  The only advantage of kmemcheck over KASan is detection of
    uninitialized memory reads.

    Some brief performance testing showed that kasan could be
    x500-x600 times faster than kmemcheck:

$ netperf -l 30
		MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
		Recv   Send    Send
		Socket Socket  Message  Elapsed
		Size   Size    Size     Time     Throughput
		bytes  bytes   bytes    secs.    10^6bits/sec

no debug:	87380  16384  16384    30.00    41624.72

kasan inline:	87380  16384  16384    30.00    12870.54

kasan outline:	87380  16384  16384    30.00    10586.39

kmemcheck: 	87380  16384  16384    30.03      20.23

  - Also kmemcheck couldn't work on several CPUs.  It always sets
    number of CPUs to 1.  KASan doesn't have such limitation.

DEBUG_PAGEALLOC:
	- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
	  granularity level, so it able to find more bugs.

SLUB_DEBUG (poisoning, redzones):
	- SLUB_DEBUG has lower overhead than KASan.

	- SLUB_DEBUG in most cases are not able to detect bad reads,
	  KASan able to detect both reads and writes.

	- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
	  bugs only on allocation/freeing of object. KASan catch
	  bugs right before it will happen, so we always know exact
	  place of first bad read/write.

[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies

Based on work by Andrey Konovalov.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.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>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 209 insertions, 0 deletions

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
new file mode 100644
index 000000000000..5835d69563f5
--- /dev/null
+++ b/mm/kasan/report.c
@@ -0,0 +1,209 @@
+/*
+ * This file contains error reporting code.
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Author: Andrey Ryabinin <a.ryabinin@samsung.com>
+ *
+ * Some of code borrowed from https://github.com/xairy/linux by
+ *        Andrey Konovalov <adech.fo@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/kasan.h>
+
+#include "kasan.h"
+
+/* Shadow layout customization. */
+#define SHADOW_BYTES_PER_BLOCK 1
+#define SHADOW_BLOCKS_PER_ROW 16
+#define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
+#define SHADOW_ROWS_AROUND_ADDR 2
+
+static const void *find_first_bad_addr(const void *addr, size_t size)
+{
+        u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
+        const void *first_bad_addr = addr;
+
+        while (!shadow_val && first_bad_addr < addr + size) {
+                first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
+                shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
+        }
+        return first_bad_addr;
+}
+
+static void print_error_description(struct kasan_access_info *info)
+{
+        const char *bug_type = "unknown crash";
+        u8 shadow_val;
+
+        info->first_bad_addr = find_first_bad_addr(info->access_addr,
+                                                info->access_size);
+
+        shadow_val = *(u8 *)kasan_mem_to_shadow(info->first_bad_addr);
+
+        switch (shadow_val) {
+        case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
+                bug_type = "out of bounds access";
+                break;
+        }
+
+        pr_err("BUG: KASan: %s in %pS at addr %p\n",
+                bug_type, (void *)info->ip,
+                info->access_addr);
+        pr_err("%s of size %zu by task %s/%d\n",
+                info->is_write ? "Write" : "Read",
+                info->access_size, current->comm, task_pid_nr(current));
+}
+
+static void print_address_description(struct kasan_access_info *info)
+{
+        dump_stack();
+}
+
+static bool row_is_guilty(const void *row, const void *guilty)
+{
+        return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
+}
+
+static int shadow_pointer_offset(const void *row, const void *shadow)
+{
+        /* The length of ">ff00ff00ff00ff00: " is
+         *    3 + (BITS_PER_LONG/8)*2 chars.
+         */
+        return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
+                (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
+}
+
+static void print_shadow_for_address(const void *addr)
+{
+        int i;
+        const void *shadow = kasan_mem_to_shadow(addr);
+        const void *shadow_row;
+
+        shadow_row = (void *)round_down((unsigned long)shadow,
+                                        SHADOW_BYTES_PER_ROW)
+                - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
+
+        pr_err("Memory state around the buggy address:\n");
+
+        for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
+                const void *kaddr = kasan_shadow_to_mem(shadow_row);
+                char buffer[4 + (BITS_PER_LONG/8)*2];
+
+                snprintf(buffer, sizeof(buffer),
+                        (i == 0) ? ">%p: " : " %p: ", kaddr);
+
+                kasan_disable_current();
+                print_hex_dump(KERN_ERR, buffer,
+                        DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
+                        shadow_row, SHADOW_BYTES_PER_ROW, 0);
+                kasan_enable_current();
+
+                if (row_is_guilty(shadow_row, shadow))
+                        pr_err("%*c\n",
+                                shadow_pointer_offset(shadow_row, shadow),
+                                '^');
+
+                shadow_row += SHADOW_BYTES_PER_ROW;
+        }
+}
+
+static DEFINE_SPINLOCK(report_lock);
+
+void kasan_report_error(struct kasan_access_info *info)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&report_lock, flags);
+        pr_err("================================="
+                "=================================\n");
+        print_error_description(info);
+        print_address_description(info);
+        print_shadow_for_address(info->first_bad_addr);
+        pr_err("================================="
+                "=================================\n");
+        spin_unlock_irqrestore(&report_lock, flags);
+}
+
+void kasan_report_user_access(struct kasan_access_info *info)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&report_lock, flags);
+        pr_err("================================="
+                "=================================\n");
+        pr_err("BUG: KASan: user-memory-access on address %p\n",
+                info->access_addr);
+        pr_err("%s of size %zu by task %s/%d\n",
+                info->is_write ? "Write" : "Read",
+                info->access_size, current->comm, task_pid_nr(current));
+        dump_stack();
+        pr_err("================================="
+                "=================================\n");
+        spin_unlock_irqrestore(&report_lock, flags);
+}
+
+void kasan_report(unsigned long addr, size_t size,
+                bool is_write, unsigned long ip)
+{
+        struct kasan_access_info info;
+
+        if (likely(!kasan_enabled()))
+                return;
+
+        info.access_addr = (void *)addr;
+        info.access_size = size;
+        info.is_write = is_write;
+        info.ip = ip;
+        kasan_report_error(&info);
+}
+
+
+#define DEFINE_ASAN_REPORT_LOAD(size)                     \
+void __asan_report_load##size##_noabort(unsigned long addr) \
+{                                                         \
+        kasan_report(addr, size, false, _RET_IP_);        \
+}                                                         \
+EXPORT_SYMBOL(__asan_report_load##size##_noabort)
+
+#define DEFINE_ASAN_REPORT_STORE(size)                     \
+void __asan_report_store##size##_noabort(unsigned long addr) \
+{                                                          \
+        kasan_report(addr, size, true, _RET_IP_);          \
+}                                                          \
+EXPORT_SYMBOL(__asan_report_store##size##_noabort)
+
+DEFINE_ASAN_REPORT_LOAD(1);
+DEFINE_ASAN_REPORT_LOAD(2);
+DEFINE_ASAN_REPORT_LOAD(4);
+DEFINE_ASAN_REPORT_LOAD(8);
+DEFINE_ASAN_REPORT_LOAD(16);
+DEFINE_ASAN_REPORT_STORE(1);
+DEFINE_ASAN_REPORT_STORE(2);
+DEFINE_ASAN_REPORT_STORE(4);
+DEFINE_ASAN_REPORT_STORE(8);
+DEFINE_ASAN_REPORT_STORE(16);
+
+void __asan_report_load_n_noabort(unsigned long addr, size_t size)
+{
+        kasan_report(addr, size, false, _RET_IP_);
+}
+EXPORT_SYMBOL(__asan_report_load_n_noabort);
+
+void __asan_report_store_n_noabort(unsigned long addr, size_t size)
+{
+        kasan_report(addr, size, true, _RET_IP_);
+}
+EXPORT_SYMBOL(__asan_report_store_n_noabort);