linux-kernel - RE: AW: [PATCH] amd64: Fix csum_partial_copy

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Date:   Sun, 22 Oct 2023 11:03:39 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Al Viro' <viro@...iv.linux.org.uk>,
        Eric Dumazet <edumazet@...gle.com>
CC:     gus Gusenleitner Klaus <gus@...a.com>,
        Al Viro <viro@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: RE: AW: [PATCH] amd64: Fix csum_partial_copy_generic()

From: Al Viro
> Sent: 21 October 2023 23:22
> 
> > I don't think -rc7 is a good time for that, though.  At the
> > very least it needs a review on linux-arch - I think I hadn't
> > fucked the ABI for returning u64 up, but...
> >
> > Anyway, completely untested patch follows:
> 
> ... and now something that at least builds (with some brainos fixed); it's still
> slightly suboptimal representation on big-endian 32bit - there it would be better to
> have have the csum in upper half of the 64bit getting returned and use the lower
> half as fault indicator, but dealing with that cleanly takes some massage of
> includes in several places, so I'd left that alone for now.  In any case, the
> overhead of that is pretty much noise.
> 
> diff --git a/arch/alpha/include/asm/checksum.h b/arch/alpha/include/asm/checksum.h
> index 99d631e146b2..80c57b370edb 100644
> --- a/arch/alpha/include/asm/checksum.h
> +++ b/arch/alpha/include/asm/checksum.h
> @@ -43,7 +43,7 @@ extern __wsum csum_partial(const void *buff, int len, __wsum sum);
>   */
>  #define _HAVE_ARCH_COPY_AND_CSUM_FROM_USER
>  #define _HAVE_ARCH_CSUM_AND_COPY
> -__wsum csum_and_copy_from_user(const void __user *src, void *dst, int len);
> +__u64 csum_and_copy_from_user(const void __user *src, void *dst, int len);
...
> +			return -1;

If you are going to return -1 the return type should be signed.

	David

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