linux-kernel - Re: [PATCH 1/4] x86/crypto: camellia: Fix function prototypes

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Message-ID: <15bd0d05-e046-1b35-9f14-91e507e6b162@suse.de>
Date:   Mon, 16 Apr 2018 11:35:58 -0300
From:   João Moreira <jmoreira@...e.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, herbert@...dor.apana.org.au, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        gregkh@...uxfoundation.org, keescook@...omium.org
Subject: Re: [PATCH 1/4] x86/crypto: camellia: Fix function prototypes

> 
>> +static inline void camellia_enc_blk(void *ctx, u8 *dst, const u8 *src)
>>   {
>> -	__camellia_enc_blk(ctx, dst, src, false);
>> +	__camellia_enc_blk((struct camellia_ctx *) ctx, dst, src, false);
>>   }
> 
> I don't see how this is an improvement: instead of having a proper type there's
> now an opaque type and an ugly (and dangerous) type cast.
> 
> What does "compatible with CFI requirements" mean?

For "compatible with CFI requirements", I meant: given a set of 
functions that are invoked through a given set of pointers, all 
functions and pointers in these sets have the same prototype. I added a 
note about this CFI heuristic in the cover letter, but I guess I should 
have been clearer there and added something more substantial to the 
commit message.

Regarding the changes, this was the most straight-forward way I found to 
make the sources compliant with the above, not requiring deeper semantic 
changes to the underneath invoking code. On the other hand, I agree that 
there is a collateral damage and that an ideal fix would be the other 
way around -- removing the opaque type from the pointer instead of 
adding it to the functions.

I'll try to think of another way and send if I come to something.

Tks,
João.