Messages in this thread | | | Subject | Re: [PATCH v2 0/2] mm/kasan: dump alloc/free stack for page allocator | From | Vlastimil Babka <> | Date | Mon, 9 Sep 2019 15:07:45 +0200 |
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On 9/9/19 10:24 AM, walter-zh.wu@mediatek.com wrote: > From: Walter Wu <walter-zh.wu@mediatek.com> > > This patch is KASAN report adds the alloc/free stacks for page allocator > in order to help programmer to see memory corruption caused by page. > > By default, KASAN doesn't record alloc and free stack for page allocator. > It is difficult to fix up page use-after-free or dobule-free issue. > > Our patchsets will record the last stack of pages. > It is very helpful for solving the page use-after-free or double-free. > > KASAN report will show the last stack of page, it may be: > a) If page is in-use state, then it prints alloc stack. > It is useful to fix up page out-of-bound issue.
I still disagree with duplicating most of page_owner functionality for the sake of using a single stack handle for both alloc and free (while page_owner + debug_pagealloc with patches in mmotm uses two handles). It reduces the amount of potentially important debugging information, and I really doubt the u32-per-page savings are significant, given the rest of KASAN overhead.
> BUG: KASAN: slab-out-of-bounds in kmalloc_pagealloc_oob_right+0x88/0x90 > Write of size 1 at addr ffffffc0d64ea00a by task cat/115 > ... > Allocation stack of page: > set_page_stack.constprop.1+0x30/0xc8 > kasan_alloc_pages+0x18/0x38 > prep_new_page+0x5c/0x150 > get_page_from_freelist+0xb8c/0x17c8 > __alloc_pages_nodemask+0x1a0/0x11b0 > kmalloc_order+0x28/0x58 > kmalloc_order_trace+0x28/0xe0 > kmalloc_pagealloc_oob_right+0x2c/0x68 > > b) If page is freed state, then it prints free stack. > It is useful to fix up page use-after-free or double-free issue. > > BUG: KASAN: use-after-free in kmalloc_pagealloc_uaf+0x70/0x80 > Write of size 1 at addr ffffffc0d651c000 by task cat/115 > ... > Free stack of page: > kasan_free_pages+0x68/0x70 > __free_pages_ok+0x3c0/0x1328 > __free_pages+0x50/0x78 > kfree+0x1c4/0x250 > kmalloc_pagealloc_uaf+0x38/0x80 > > This has been discussed, please refer below link. > https://bugzilla.kernel.org/show_bug.cgi?id=203967
That's not a discussion, but a single comment from Dmitry, which btw contains "provide alloc *and* free stacks for it" ("it" refers to page, emphasis mine). It would be nice if he or other KASAN guys could clarify.
> Changes since v1: > - slim page_owner and move it into kasan > - enable the feature by default > > Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com> > --- > include/linux/kasan.h | 1 + > lib/Kconfig.kasan | 2 ++ > mm/kasan/common.c | 32 ++++++++++++++++++++++++++++++++ > mm/kasan/kasan.h | 5 +++++ > mm/kasan/report.c | 27 +++++++++++++++++++++++++++ > 5 files changed, 67 insertions(+)
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