netdev - Re: [PATCH net-next v4] net: skb: prevent the split of kfree_skb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 18 Aug 2022 10:09:46 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     menglong8.dong@...il.com
Cc:     miguel.ojeda.sandonis@...il.com, ojeda@...nel.org,
        ndesaulniers@...gle.com, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, asml.silence@...il.com, imagedong@...cent.com,
        luiz.von.dentz@...el.com, vasily.averin@...ux.dev,
        jk@...econstruct.com.au, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH net-next v4] net: skb: prevent the split of
 kfree_skb_reason() by gcc

On Tue, 16 Aug 2022 11:28:46 +0800 menglong8.dong@...il.com wrote:
> From: Menglong Dong <imagedong@...cent.com>
> 
> Sometimes, gcc will optimize the function by spliting it to two or
> more functions. In this case, kfree_skb_reason() is splited to
> kfree_skb_reason and kfree_skb_reason.part.0. However, the
> function/tracepoint trace_kfree_skb() in it needs the return address
> of kfree_skb_reason().
> 
> This split makes the call chains becomes:
>   kfree_skb_reason() -> kfree_skb_reason.part.0 -> trace_kfree_skb()
> 
> which makes the return address that passed to trace_kfree_skb() be
> kfree_skb().
> 
> Therefore, prevent this kind of optimization to kfree_skb_reason() by
> making the optimize level to "O1". I think these should be better
> method instead of this "O1", but I can't figure it out......
> 
> This optimization CAN happen, which depend on the behavior of gcc.
> I'm not able to reproduce it in the latest kernel code, but it happens
> in my kernel of version 5.4.119. Maybe the latest code already do someting
> that prevent this happen?
> 
> Signed-off-by: Menglong Dong <imagedong@...cent.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>

Sorry for a late and possibly off-topic chime in, is the compiler
splitting it because it thinks that skb_unref() is going to return 
true? I don't think that's the likely case, so maybe we're better 
off wrapping that skb_unref() in unlikely()?