Re: [PATCH v3] mm/kasan: dump alloc and free stack for page allocator

Qian Cai
2019-09-11T15:19:24Z

> On Sep 11, 2019, at 4:39 AM, Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> This patch is KASAN's report adds the alloc/free stack for page allocator
> in order to help programmer to see memory corruption caused by the page.
>
> By default, KASAN doesn't record alloc or free stack for page allocator.
> It is difficult to fix up the page use-after-free or double-free issue.
>
> We add the following changing:
> 1) KASAN enable PAGE_OWNER by default to get the alloc stack of the page.
> 2) Add new feature option to get the free stack of the page.
>
> The new feature KASAN_DUMP_PAGE depends on DEBUG_PAGEALLOC, it will help
> to record free stack of the page, it is very helpful for solving the page
> use-after-free or double-free issue.
>
> When KASAN_DUMP_PAGE is enabled then KASAN's report will show the last
> alloc and free stack of the page, it should be:
>
> BUG: KASAN: use-after-free in kmalloc_pagealloc_uaf+0x70/0x80
> Write of size 1 at addr ffffffc0d60e4000 by task cat/115
> ...
> prep_new_page+0x1c8/0x218
> get_page_from_freelist+0x1ba0/0x28d0
> __alloc_pages_nodemask+0x1d4/0x1978
> kmalloc_order+0x28/0x58
> kmalloc_order_trace+0x28/0xe0
> kmalloc_pagealloc_uaf+0x2c/0x80
> page last free stack trace:
> __free_pages_ok+0x116c/0x1630
> __free_pages+0x50/0x78
> kfree+0x1c4/0x250
> kmalloc_pagealloc_uaf+0x38/0x80
>
> Changes since v1:
> - slim page_owner and move it into kasan
> - enable the feature by default
>
> Changes since v2:
> - enable PAGE_OWNER by default
> - use DEBUG_PAGEALLOC to get page information
>
> cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> cc: Vlastimil Babka <vbabka@suse.cz>
> cc: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> ---
> lib/Kconfig.kasan | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index 4fafba1a923b..4d59458c0c5a 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -41,6 +41,7 @@ config KASAN_GENERIC
> select SLUB_DEBUG if SLUB
> select CONSTRUCTORS
> select STACKDEPOT
> + select PAGER_OWNER
> help
> Enables generic KASAN mode.
> Supported in both GCC and Clang. With GCC it requires version 4.9.2
> @@ -63,6 +64,7 @@ config KASAN_SW_TAGS
> select SLUB_DEBUG if SLUB
> select CONSTRUCTORS
> select STACKDEPOT
> + select PAGER_OWNER
> help
> Enables software tag-based KASAN mode.
> This mode requires Top Byte Ignore support by the CPU and therefore
> @@ -135,6 +137,19 @@ config KASAN_S390_4_LEVEL_PAGING
> to 3TB of RAM with KASan enabled). This options allows to force
> 4-level paging instead.
>
> +config KASAN_DUMP_PAGE
> + bool "Dump the last allocation and freeing stack of the page"
> + depends on KASAN
> + select DEBUG_PAGEALLOC
> + help
> + By default, KASAN enable PAGE_OWNER only to record alloc stack
> + for page allocator. It is difficult to fix up page use-after-free
> + or double-free issue.
> + This feature depends on DEBUG_PAGEALLOC, it will extra record
> + free stack of page. It is very helpful for solving the page
> + use-after-free or double-free issue.
> + This option will have a small memory overhead.
> +
> config TEST_KASAN
> tristate "Module for testing KASAN for bug detection"
> depends on m && KASAN
> —

The new config looks redundant and confusing. It looks to me more of a document update
in Documentation/dev-tools/kasan.txt to educate developers to select PAGE_OWNER and
DEBUG_PAGEALLOC if needed.