Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 13 Dec 2016 08:40:00 -0800 | Subject | Re: [PATCH] keys/encrypted: Fix two crypto-on-the-stack bugs |
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[add some people who might know]
On Tue, Dec 13, 2016 at 4:20 AM, David Laight <David.Laight@aculab.com> wrote: > From: Andy Lutomirski >> Sent: 12 December 2016 20:53 >> The driver put a constant buffer of all zeros on the stack and >> pointed a scatterlist entry at it in two places. This doesn't work >> with virtual stacks. Use a static 16-byte buffer of zeros instead. > ... > > I didn't think you could dma from static data either.
According to lib/dma-debug.c, you can't dma to or from kernel text or rodata, but you can dma to or from kernel bss or data. So empty_zero_page should be okay, because it's not rodata right now.
But I think this is rather silly. Joerg, Linus, etc: would it be okay to change lib/dma-debug.c to allow DMA *from* rodata? After all, rodata is ordinary memory, is backed by struct page, etc. And DMA from the zero page had better be okay because I think it happens if you mmap some zeros, don't write to them, and then direct I/O them to a device. Then I could also move empty_zero_page to rodata.
--Andy
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