Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK

From	Herbert Xu <herbert@gondor.apana.org.au>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK
Date	2016-12-10 09:20 +0100
Message-ID	<sML2W-6Rq-9@gated-at.bofh.it> (permalink)
References	<sMJ18-57L-13@gated-at.bofh.it>
Organization	Core

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Why did you drop me from the CC list when you were replying to
my email?

Eric Biggers <ebiggers3@gmail.com> wrote:
> On Sat, Dec 10, 2016 at 01:32:08PM +0800, Herbert Xu wrote:
>
>> Are you sure? Any instance of *_ON_STACK must only be used with
>> sync algorithms and most drivers under drivers/crypto declare
>> themselves as async.
> 
> Why exactly is that?  Obviously, it wouldn't work if you returned from the stack
> frame before the request completed, but does anything stop someone from using an
> *_ON_STACK() request and then waiting for the request to complete before
> returning from the stack frame?

The *_ON_STACK variants (except SHASH of course) were simply hacks
to help legacy crypto API users to cope with the new async interface.
In general we should avoid using the sync interface when possible.

It's a bad idea for the obvious reason that most of our async
algorithms want to DMA and that doesn't work very well when you're
using memory from the stack.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Thread

Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 00:10 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-10 06:30 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 06:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:10 +0100
        Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 09:20 +0100
          Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 09:40 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 06:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-10 15:50 +0100
        Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-10 18:50 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:00 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-11 20:20 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-12 00:40 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-12 19:40 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-13 04:40 +0100
      Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-13 18:10 +0100
        Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-14 06:00 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-13 04:50 +0100

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