Messages in this thread | | | Date | Mon, 17 Apr 2017 10:48:03 +0900 | From | Sergey Senozhatsky <> | Subject | copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram: do not use copy_page with non-page alinged address") |
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Hello,
I'll fork it into a separate thread and Cc more MM people. sorry for top-posting.
Minchan reported that doing copy_page() on a kmalloc(PAGE_SIZE) page with DEBUG_SLAB enabled can cause a memory corruption (See below or lkml.kernel.org/r/1492042622-12074-2-git-send-email-minchan@kernel.org )
that's an interesting problem. arm64 copy_page(), for instance, wants src and dst to be page aligned, which is reasonable, while generic copy_page(), on the contrary, simply does memcpy(). there are, probably, other callpaths that do copy_page() on kmalloc-ed pages and I'm wondering if there is some sort of a generic fix to the problem.
> > On (04/13/17 09:17), Minchan Kim wrote: > > > The copy_page is optimized memcpy for page-alinged address. > > > If it is used with non-page aligned address, it can corrupt memory which > > > means system corruption. With zram, it can happen with > > > > > > 1. 64K architecture > > > 2. partial IO > > > 3. slub debug > > > > > > Partial IO need to allocate a page and zram allocates it via kmalloc. > > > With slub debug, kmalloc(PAGE_SIZE) doesn't return page-size aligned > > > address. And finally, copy_page(mem, cmem) corrupts memory. > > > > which would be the case for many other copy_page() calls in the kernel. > > right? if so - should the fix be in copy_page() then? > > I thought about it but was not sure it's good idea by several reasons > (but don't want to discuss it in this thread). > > Anyway, it's stable stuff so I don't want to make the patch bloat. > If you believe it is right direction and valuable, you could be > a volunteer. :)
-ss
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