linux-kernel - Re: [PATCH] parisc: Fix csum_ipv6

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Date: Fri, 16 Feb 2024 07:31:17 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Helge Deller <deller@...nel.org>
Cc: Helge Deller <deller@....de>,
 "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
 linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
 Charlie Jenkins <charlie@...osinc.com>, Palmer Dabbelt <palmer@...osinc.com>
Subject: Re: [PATCH] parisc: Fix csum_ipv6_magic on 64-bit systems

Hi Helge,

On 2/16/24 04:38, Helge Deller wrote:
> * Guenter Roeck <linux@...ck-us.net>:
>> hppa 64-bit systems calculates the IPv6 checksum using 64-bit add
>> operations. The last add folds protocol and length fields into the 64-bit
>> result. While unlikely, this operation can overflow. The overflow can be
>> triggered with a code sequence such as the following.
>>
>> 	/* try to trigger massive overflows */
>> 	memset(tmp_buf, 0xff, sizeof(struct in6_addr));
>> 	csum_result = csum_ipv6_magic((struct in6_addr *)tmp_buf,
>> 				      (struct in6_addr *)tmp_buf,
>> 				      0xffff, 0xff, 0xffffffff);
>>
>> Fix the problem by adding any overflows from the final add operation into
>> the calculated checksum. Fortunately, we can do this without additional
>> cost by replacing the add operation used to fold the checksum into 32 bit
>> with "add,dc" to add in the missing carry.
> 
> 
> Gunter,
> 
> Thanks for your patch for 32- and 64-bit systems.
> But I think it's time to sunset the parisc inline assembly for ipv4/ipv6
> checksumming.
> The patch below converts the code to use standard C-coding (taken from the
> s390 header file) and it survives the v8 lib/checksum patch.
> 
> Opinions?
> 

Works for me.

> Helge
> 
> Subject: [PATCH] parisc: Fix csum_ipv6_magic on 32- and 64-bit machines
> 
> Guenter noticed that the 32- and 64-bit checksum functions may calculate
> wrong values under certain circumstances. He fixed it by usining

using

> corrected carry-flags added, but overall I think it's better to convert
> away from inline assembly to generic C-coding.  That way the code is
> much cleaner and the compiler can do much better optimizations based on
> the target architecture (32- vs. 64-bit). Furthermore, the compiler
> generates nowadays much better code, so inline assembly usually won't
> give any benefit any longer.
> 
> Signed-off-by: Helge Deller <deller@....de>
> Noticed-by: Guenter Roeck <linux@...ck-us.net>

That would be a new tag. Maybe use "Reported-by:", or just drop it.

Maybe also consider adding

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Other than that,

Tested-by: Guenter Roeck <linux@...ck-us.net>

Thanks,
Guenter