在kernel中使用内存检测
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目录
一般的内存访问错误如下：
- 越界访问
- 访问已经释放的内存
- 重复释放
- 内存泄露
- 栈溢出
在内核中提供了内存检测的工具slub与kasan，在开发时可以将检测的功能打开。
一、slub内存检测
在linux内核中，对于小块内存分配，大量使用slab/slub分配器，在内存访问中比较容易出错的地方如下：
- 访问已经释放的内存
- 越界访问
- 重复释放
内核配置
CONFIG_SLUB=y
CONFIG_SLUB_DEBUG_ON=y
CONFIG_SLUB_STATS=y
使用的工具tools/vm/slabinfo
1、越界访问
static noinline void __init kmalloc_pagealloc_oob_right(void)
char *ptr;
size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
/* Allocate a chunk that does not fit into a SLUB cache to trigger
* the page allocator fallback.
*/
pr_info("kmalloc pagealloc allocation: out-of-bounds to right\\n");
ptr = kmalloc(size, GFP_KERNEL);
if (!ptr)
pr_err("Allocation failed\\n");
return;
ptr[size] = 0;
kfree(ptr);
2、释放后再访问
static noinline void __init kmalloc_pagealloc_uaf(void)
char *ptr;
size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
pr_info("kmalloc pagealloc allocation: use-after-free\\n");
ptr = kmalloc(size, GFP_KERNEL);
if (!ptr)
pr_err("Allocation failed\\n");
return;
kfree(ptr);
ptr[0] = 0;
3、无效的释放
static noinline void __init kmalloc_pagealloc_invalid_free(void)
char *ptr;
size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
pr_info("kmalloc pagealloc allocation: invalid-free\\n");
ptr = kmalloc(size, GFP_KERNEL);
if (!ptr)
pr_err("Allocation failed\\n");
return;
kfree(ptr + 1);
4、实验输出
- 内存越界访问Redzone overwritten、Object padding overwritten
- 重复释放Object already free
- 访问已释放内存为Posion overwritten
# insmod slub3.ko
[ 997.342740] :access free memory
benshushu:slub_test_3# [ 997.436270] =============================================================================
[ 997.437705] BUG kmalloc-128 (Tainted: G B OE ): Redzone overwritten
[ 997.438153] -----------------------------------------------------------------------------
[ 997.438153]
[ 997.440009] INFO: 0x000000001c0937b9-0x0000000065391b57. First byte 0x55 instead of 0xcc
[ 997.442519] INFO: Allocated in create_slub_error+0x30/0x94 [slub3] age=63120 cpu=1 pid=1602
有的时候需要使用slabinfo -v才能输出错误
slub_test# ./slabinfo -v
[ 1112.602383] =============================================================================
[ 1112.602945] BUG kmalloc-128 (Tainted: G B OE ): Redzone overwritten
[ 1112.603254] -----------------------------------------------------------------------------
[ 1112.603254]
[ 1112.603773] INFO: 0x00000000583020f8-0x00000000583020f8. First byte 0x55 instead of 0xcc
[ 1112.604214] INFO: Allocated in create_slub_error+0x34/0xdc [slub4] age=4071 cpu=0 pid=1687
[ 1112.604661] __slab_alloc+0x64/0xb0
[ 1112.604822] __kmalloc+0x558/0xee4
[ 1112.605002] create_slub_error+0x34/0xdc [slub4]
二、KASAN 内存检测
KASAN(Kernal Address SANtizer)在Linux4.0版本中合并到官方的内核。是动态检测内存错误的工具。可以检查内存越界和使用已经释放的内存等问题。KASAN比kmemcheck工具检测速度快。
内核配置
CONFIG_HAVE_ARCH_KASAN=y
CONFIG_KASAN=y
CONFIG_KASAN_OUTLINE=y
CONFIG_KASAN_INLINE=y
CONFIG_TEST_KASAN=m //编译test_kasan.ko测试模块
内核源码中的测试程序/lib/test_ksacn.c
static int __init kmalloc_tests_init(void)
/*
* Temporarily enable multi-shot mode. Otherwise, we'd only get a
* report for the first case.
*/
bool multishot = kasan_save_enable_multi_shot();
kmalloc_oob_right();
kmalloc_oob_left();
kmalloc_node_oob_right();
#ifdef CONFIG_SLUB
kmalloc_pagealloc_oob_right();
kmalloc_pagealloc_uaf();
kmalloc_pagealloc_invalid_free();
#endif
kmalloc_large_oob_right();
kmalloc_oob_krealloc_more();
kmalloc_oob_krealloc_less();
kmalloc_oob_16();
kmalloc_oob_in_memset();
kmalloc_oob_memset_2();
kmalloc_oob_memset_4();
kmalloc_oob_memset_8();
kmalloc_oob_memset_16();
kmalloc_uaf();
kmalloc_uaf_memset();
kmalloc_uaf2();
kmem_cache_oob();
memcg_accounted_kmem_cache();
kasan_stack_oob();
kasan_global_oob();
kasan_alloca_oob_left();
kasan_alloca_oob_right();
ksize_unpoisons_memory();
copy_user_test();
use_after_scope_test();
kmem_cache_double_free();
kmem_cache_invalid_free();
kasan_memchr();
kasan_memcmp();
kasan_strings();
kasan_restore_multi_shot(multishot);
return -EAGAIN;
从上选择其中两个解析
1、数组越界
static noinline void __init kmalloc_oob_right(void)
char *ptr;
size_t size = 123;
pr_info("out-of-bounds to right\\n");
ptr = kmalloc(size, GFP_KERNEL);
if (!ptr)
pr_err("Allocation failed\\n");
return;
ptr[size] = 'x';
kfree(ptr);
2、栈的越界访问
static noinline void __init kasan_stack_oob(void)
char stack_array[10];
volatile int i = 0;
char *p = &stack_array[ARRAY_SIZE(stack_array) + i];
pr_info("out-of-bounds on stack\\n");
*(volatile char *)p;
3、实验输出
1）在内核中同时开启ksasn与slub的检测的检测，内存错误优先被kasan检测到，如下所示：
slub_test_1# insmod slub1.ko
[ 744.870946] slub1: loading out-of-tree module taints kernel.
[ 744.886482] slub1: module verification failed: signature and/or required key missing - tainting kernel
[ 744.958499] module init
[ 744.959688] ==================================================================
[ 744.962726] BUG: KASAN: slab-out-of-bounds in create_slub_error+0x6c/0x78 [slub1]
[ 744.963528] Write of size 130 at addr ffff800019ea1200 by task insmod/1602
[ 744.964141] slub_test_2# insmod slub2.ko
[ 874.303487] my module init
[ 874.304834] ben:double free test
[ 874.305266] ==================================================================
[ 874.306672] BUG: KASAN: double-free or invalid-free in create_slub_error+0x98/0xa4 [slub2]
[ 874.307269]
2）将test_kasan.ko加载后，所有的打印输出有所缩减，把检测到的提示错误保留
slab-out-of-bounds， use-after-free，double-free or invalid-free，alloca-out-of-bounds
insmod test_kasan.ko
[ 96.717377] test_kasan: module verification failed: signature and/or required key missing - tainting kernel
[ 96.788908] kasan test: kmalloc_oob_right out-of-bounds to right
[ 96.790675] ==================================================================
[ 96.794556] BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xc8/0xe4 [test_kasan]
[ 96.796122] Write of size 1 at addr ffff80001cebcffb by task insmod/569
[ 96.796619]
[ 96.797727] CPU: 0 PID: 569 Comm: insmod Kdump: loaded Tainted: G E 5.0.0+ #2
[ 96.798290] Hardware name: linux,dummy-virt (DT)
[ 96.799205] Call trace:
[ 96.800667] dump_backtrace+0x0/0x97c
[ 96.801030] show_stack+0x24/0x30
[ 96.801283] __dump_stack+0x20/0x2c
[ 96.801673] dump_stack+0x318/0x690
[ 96.802003] print_address_description+0x38/0x42c
[ 96.802371] kasan_report+0x194/0x1e8
[ 96.802727] __asan_report_store1_noabort+0x30/0x3c
[ 96.803462] kmalloc_oob_right+0xc8/0xe4 [test_kasan]
[ 96.805821] kmalloc_tests_init+0x14/0x640 [test_kasan]
[ 96.806516] do_one_initcall+0xc8c/0x1ca4
[ 96.806802] do_init_module+0x1d8/0x784
[ 96.807130] load_module+0x1210/0x1920
[ 96.808033] __se_sys_finit_module+0x1c8/0x224
[ 96.808527] __arm64_sys_finit_module+0xbc/0xc8
[ 96.809137] __invoke_syscall+0x24/0x2c
[ 96.809389] invoke_syscall+0xcc/0x128
[ 96.809557] el0_svc_common+0x1c4/0x2d0
[ 96.809746] el0_svc_handler+0x91c/0x960
[ 96.809946] el0_svc+0x8/0xc
[ 96.810422]
[ 96.810770] Allocated by task 569:
[ 96.811245] __kasan_kmalloc+0x148/0x290
[ 96.811886] kasan_kmalloc+0x30/0x38
[ 96.812672] __kmalloc+0xea4/0xee4
[ 96.813049] kmalloc_oob_right+0x48/0xe4 [test_kasan]
[ 96.813561] kmalloc_tests_init+0x14/0x640 [test_kasan]
[ 96.814003] do_one_initcall+0xc8c/0x1ca4
[ 96.814363] do_init_module+0x1d8/0x784
[ 96.814589] load_module+0x1210/0x1920
[ 96.814829] __se_sys_finit_module+0x1c8/0x224
[ 96.815093] __arm64_sys_finit_module+0xbc/0xc8
[ 96.816164] __invoke_syscall+0x24/0x2c
[ 96.816581] invoke_syscall+0xcc/0x128
[ 96.817567] el0_svc_common+0x1c4/0x2d0
[ 96.817836] el0_svc_handler+0x91c/0x960
[ 96.818363] el0_svc+0x8/0xc
[ 96.818832]
[ 96.819123] Freed by task 0:
[ 96.820128] (stack is not available)
[ 96.820582]
[ 96.820839] The buggy address belongs to the object at ffff80001cebcf80
[ 96.820839] which belongs to the cache kmalloc-128 of size 128
[ 96.821736] The buggy address is located 123 bytes inside of
[ 96.821736] 128-byte region [ffff80001cebcf80, ffff80001cebd000)
[ 96.823027] The buggy address belongs to the page:
[ 96.827418] page:ffff7e000073af00 count:1 mapcount:0 mapping:ffff800021c0c400 index:0xffff80001cebed80 compound_mapcount: 0
[ 96.830608] flags: 0xffff00000010200(slab|head)
[ 96.831566] raw: 0ffff00000010200 ffff7e0000752f08 ffff800021c03c90 ffff800021c0c400
[ 96.833056] raw: ffff80001cebed80 0000000000190012 00000001ffffffff 0000000000000000
[ 96.833864] page dumped because: kasan: bad access detected
[ 96.834505]
[ 96.834866] Memory state around the buggy address:
[ 96.836134] ffff80001cebce80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 96.837813] ffff80001cebcf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 96.839023] >ffff80001cebcf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03
[ 96.840070] ^
[ 96.840943] ffff80001cebd000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 96.841405] ffff80001cebd080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 96.841988] ==================================================================
[ 96.842481] Disabling lock debugging due to kernel taint
[ 96.844009] kasan test: kmalloc_oob_left out-of-bounds to left
[ 96.845114] ==================================================================
[ 96.849223] BUG: KASAN: slab-out-of-bounds in kmalloc_oob_left+0xc0/0x134 [test_kasan]
[ 96.850317] Read of size 1 at addr ffff80001cebed7f by task insmod/569
[ 96.895962] ==================================================================
[ 96.898866] kasan test: kmalloc_node_oob_right kmalloc_node(): out-of-bounds to right
[ 96.902638] ==================================================================
[ 96.905146] BUG: KASAN: slab-out-of-bounds in kmalloc_node_oob_right+0xd0/0xe8 [test_kasan]
[ 96.906247] Write of size 1 at addr ffff800015826a80 by task insmod/569
[ 96.907658]
[ 96.967853] ==================================================================
[ 96.970577] kasan test: kmalloc_pagealloc_oob_right kmalloc pagealloc allocation: out-of-bounds to right
[ 96.973391] ==================================================================
[ 96.974297] BUG: KASAN: slab-out-of-bounds in kmalloc_pagealloc_oob_right+0xc8/0xe0 [test_kasan]
[ 96.976085] Write of size 1 at addr ffff80001c0be00a by task insmod/569
[ 97.009774] ==================================================================
[ 97.013784] kasan test: kmalloc_pagealloc_uaf kmalloc pagealloc allocation: use-after-free
[ 97.015457] ==================================================================
[ 97.016937] BUG: KASAN: use-after-free in kmalloc_pagealloc_uaf+0xc0/0xd0 [test_kasan]
[ 97.018264] Write of size 1 at addr ffff80001c0bc000 by task insmod/569
[ 97.021236]
[ 97.058048] ==================================================================
[ 97.062012] kasan test: kmalloc_pagealloc_invalid_free kmalloc pagealloc allocation: invalid-free
[ 97.063042] ==================================================================
[ 97.064403] BUG: KASAN: double-free or invalid-free in kmalloc_pagealloc_invalid_free+0x78/0x80 [test_kasan]
[ 97.563543] ==================================================================
[ 97.565871] kasan test: kmalloc_oob_memset_16 out-of-bounds in memset16
[ 97.566822] ==================================================================
[ 97.567581] BUG: KASAN: slab-out-of-bounds in kmalloc_oob_memset_16+0x80/0x90 [test_kasan]
[ 97.568841] Write of size 16 at addr ffff80001d4bc081 by task insmod/569
[ 97.618222] ==================================================================
[ 97.620924] kasan test: kmalloc_uaf use-after-free
[ 97.622887] ==================================================================
[ 97.624507] BUG: KASAN: use-after-free in kmalloc_uaf+0xcc/0xe0 [test_kasan]
[ 97.626212] Write of size 1 at addr ffff80001d4bc588 by task insmod/569
[ 97.627438]
[ 97.672285] ==================================================================
[ 97.673872] kasan test: kmalloc_uaf_memset use-after-free in memset
[ 97.674501] ==================================================================
[ 97.675046] BUG: KASAN: use-after-free in kmalloc_uaf_memset+0x84/0x8c [test_kasan]
[ 97.675620] Write of size 33 at addr ffff80001d4bf500 by task insmod/569
[ 97.676672] ==================================================================
[ 98.023758] kasan test: memcg_accounted_kmem_cache allocate memcg accounted object
[ 98.674484] kasan test: kasan_stack_oob out-of-bounds on stack
[ 98.675223] ==================================================================
[ 98.678286] BUG: KASAN: stack-out-of-bounds in kasan_stack_oob+0xf8/0x144 [test_kasan]
[ 98.679094] Read of size 1 at addr ffff8000197df39a by task insmod/569
[ 98.679522] [ 98.735804]
[ 98.867912] ==================================================================
[ 98.870386] kasan test: copy_user_test out-of-bounds in copy_from_user()
[ 98.871485] ==================================================================
[ 98.872960] BUG: KASAN: slab-out-of-bounds in copy_user_test+0x28c/0x8d8 [test_kasan]
[ 98.874518] Write of size 11 at addr ffff80001c007000 by task insmod/569
[ 98.875381][ 98.932274] ==================================================================
[ 98.934343] kasan test: copy_user_test out-of-bounds in copy_to_user()
[ 98.935494] ==================================================================
[ 98.936524] BUG: KASAN: slab-out-of-bounds in copy_user_test+0x500/0x8d8 [test_kasan]
[ 98.937066] Read of size 11 at addr ffff80001c007000 by task insmod/569
[ 98.938636][ 98.993046]
[ 99.049702] ==================================================================
[ 99.051988] kasan test: copy_user_test out-of-bounds in __copy_to_user()
[ 99.052711] ==================================================================
[ 99.054365] BUG: KASAN: slab-out-of-bounds in copy_user_test+0x67c/0x8d8 [test_kasan]
[ 99.056035] Read of size 11 at addr ffff80001c007000 by task insmod/569
[ 99.057768]
[ 99.297345] ==================================================================
[ 99.303983] kasan test: use_after_scope_test use-after-scope on int
[ 99.305426] kasan test: use_after_scope_test use-after-scope on array
[ 99.319414] kasan test: kmem_cache_double_free double-free on heap object
[ 99.321611] ==================================================================
[ 99.322758] BUG: KASAN: double-free or invalid-free in kmem_cache_double_free+0xc4/0xd4 [test_kasan]
[ 99.324030]
[ 99.718299] ==================================================================
[ 99.719678] kasan test: kasan_memcmp out-of-bounds in memcmp
[ 99.721512] ==================================================================
[ 99.722675] BUG: KASAN: slab-out-of-bounds in memcmp+0x7c/0x138
[ 99.723387] Read of size 1 at addr ffff80001d62b798 by task insmod/569
[ 99.723956]
[ 99.808130] ==================================================================
[ 99.810907] kasan test: kasan_strings use-after-free in strchr
[ 99.812133] ==================================================================
[ 99.812909] BUG: KASAN: use-after-free in strchr+0xd0/0xf4
[ 99.813602] Read of size 1 at addr ffff80001d629c10 by task insmod/569
[ 99.814186]
[ 100.231048] ==================================================================
[ 100.232472] kasan test: kasan_strings use-after-free in strncmp
[ 100.235615] ==================================================================
[ 100.241922] BUG: KASAN: use-after-free in strncmp+0x74/0x148
[ 100.243947] Read of size 1 at addr ffff80001d629c10 by task insmod/569
[ 100.244851]
[ 100.293083] ffff80001d629c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 100.293951] ffff80001d629d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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