linux-kernel - Re: [PATCH] x86: asm/io.h: Harden virt_to_phys/isa_virt_to

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Date:   Fri, 14 Apr 2023 20:23:39 -0700
From:   Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Stanislav Kinsburskii <stanislav.kinsburskii@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Chris Down <chris@...isdown.name>,
        Helge Deller <deller@....de>, Omar Sandoval <osandov@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: asm/io.h: Harden virt_to_phys/isa_virt_to_bus
 prototypes

On Sat, Apr 22, 2023 at 11:02:33AM +0200, Arnd Bergmann wrote:
> On Fri, Apr 14, 2023, at 11:40, Stanislav Kinsburskii wrote:
> > From: Stanislav Kinsburskii <stanislav.kinsburskii@...il.com>
> >
> > These two helper functions - virt_to_phys and isa_virt_to_bus - don't need the
> > address pointer to be mutable.
> >
> > In the same time expecting it to be mutable leads to the following build
> > warning for constant pointers:
> >
> >   warning: passing argument 1 of ‘virt_to_phys’ discards ‘const’ 
> > qualifier from pointer target type
> >
> 
> The change looks fine, and this is clearly useful for spreading
> more 'const' annotations, but I have two concerns:
> 
> - I'd really like this to be done consistently across architectures,
>   so at least the asm-generic/io.h version should get the same
>   annotation, or ideally all of them in one patch.
> 

Sure, let me come up with the a series to cover other architectures.

> - I would not describe this change itself as "hardening", as it
>   also does the opposite, when you have a pointer that is actually
>   "const" but converting it through virt_to_phys() and back
>   through phys_to_virt() ends up losing the annotation.
>

Indeen, I didn't think about this way.
Let me then just state what the change does (i.e. "Make virt_to_phys to
allow unmutable pointers"), unless you have a better option to advice.

Thanks,
Stanislav

>      Arnd