linux-kernel - Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library

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Date:   Thu, 20 Sep 2018 09:01:36 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Neves <sneves@....uc.pt>,
        Andy Lutomirski <luto@...nel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library



> On Sep 20, 2018, at 8:41 AM, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> 
> (+ Arnd, Eric)
> 
> On 18 September 2018 at 09:16, Jason A. Donenfeld <Jason@...c4.com> wrote:
> ...
> 
>> diff --git a/lib/zinc/Makefile b/lib/zinc/Makefile
>> new file mode 100644
>> index 000000000000..83dfd63988c0
>> --- /dev/null
>> +++ b/lib/zinc/Makefile
>> @@ -0,0 +1,4 @@
> 
> Apologies for not spotting these before:
> 
>> +ccflags-y := -O3
> 
> -O3 optimization has been problematic in the past, at least on x86 but
> I think on other architectures as well. Please stick with -O2.
> 
>> +ccflags-y += -Wframe-larger-than=$(if (CONFIG_KASAN),16384,8192)
> 
> There is no way we can support code in the kernel with that kind of
> stack space requirements. I will let Arnd comment on what we typically
> allow, since he deals with such issues on a regular basis.

To make matters worse, KASAN is incompatible with VMAP_STACK right now, and KASAN is not so good at detecting stack overflow.

> 
>> +ccflags-y += -D'pr_fmt(fmt)="zinc: " fmt'
>> +ccflags-$(CONFIG_ZINC_DEBUG) += -DDEBUG
>> --
>> 2.19.0
>>