linux-kernel - Re: [PATCH v3 02/22] compat: provide compat

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Date:   Tue, 07 Jan 2020 13:05:22 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Arnd Bergmann <arnd@...db.de>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        James Hogan <jhogan@...nel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Robert Richter <rric@...nel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        oprofile-list@...ts.sf.net, linux-s390@...r.kernel.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 02/22] compat: provide compat_ptr() on all architectures

Arnd Bergmann <arnd@...db.de> writes:
> In order to avoid needless #ifdef CONFIG_COMPAT checks,
> move the compat_ptr() definition to linux/compat.h
> where it can be seen by any file regardless of the
> architecture.
>
> Only s390 needs a special definition, this can use the
> self-#define trick we have elsewhere.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/arm64/include/asm/compat.h   | 17 -----------------
>  arch/mips/include/asm/compat.h    | 18 ------------------
>  arch/parisc/include/asm/compat.h  | 17 -----------------
>  arch/powerpc/include/asm/compat.h | 17 -----------------
>  arch/powerpc/oprofile/backtrace.c |  2 +-

LGTM.

Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)

One minor comment:

> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 68f79d855c3d..11083d84eb23 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -958,4 +958,22 @@ static inline bool in_compat_syscall(void) { return false; }
>  
>  #endif /* CONFIG_COMPAT */
>  
> +/*
> + * A pointer passed in from user mode. This should not
> + * be used for syscall parameters, just declare them
> + * as pointers because the syscall entry code will have
> + * appropriately converted them already.
> + */
> +#ifndef compat_ptr
> +static inline void __user *compat_ptr(compat_uptr_t uptr)
> +{
> +	return (void __user *)(unsigned long)uptr;
> +}
> +#endif
> +
> +static inline compat_uptr_t ptr_to_compat(void __user *uptr)
> +{
> +	return (u32)(unsigned long)uptr;
> +}

Is there a reason we cast to u32 directly instead of using compat_uptr_t?

cheers