linux-kernel - Re: [PATCH 1/1] cfi: Use rcu_read_{un}lock_sched

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Date:   Thu, 12 Aug 2021 20:33:27 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Sami Tolvanen <samitolvanen@...gle.com>,
        <linux-kernel@...r.kernel.org>,
        Jinlong Mao <jinlmao@...eaurora.org>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>,
        Trilok Soni <tsoni@...eaurora.org>
Subject: Re: [PATCH 1/1] cfi: Use rcu_read_{un}lock_sched_notrace

Hi Kees,

On 8/11/2021 1:10 PM, Kees Cook wrote:
> On Wed, Aug 11, 2021 at 08:59:14AM -0700, Elliot Berman wrote:
>> If rcu_read_lock_sched tracing is enabled, the tracing subsystem can
>> perform a jump which needs to be checked by CFI. For example, stm_ftrace
>> source is enabled as a module and hooks into enabled ftrace events. This
>> can cause an recursive loop where find_shadow_check_fn ->
>> rcu_read_lock_sched -> (call to stm_ftrace generates cfi slowpath) ->
>> find_shadow_check_fn -> rcu_read_lock_sched -> ...
>>
>> To avoid the recursion, either the ftrace codes needs to be marked with
>> __no_cfi or CFI should not trace. Use the "_notrace" in CFI to avoid
>> tracing so that CFI can guard ftrace.
>>
>> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
> 
> Thanks for this patch! While applying it I noticed that the DKIM
> signature failed. This is actually even visible in the lore archive:
> https://lore.kernel.org/lkml/20210811155914.19550-1-quic_eberman@quicinc.com/raw
> (DKIM_INVALID)
> 
> $ b4 am -tls https://lore.kernel.org/lkml/20210811155914.19550-1-quic_eberman@quicinc.com/
> Grabbing thread from lore.kernel.org/lkml/20210811155914.19550-1-quic_eberman%40quicinc.com/t.mbox.gz
> Analyzing 2 messages in the thread
> Checking attestation on all messages, may take a moment...
> ---
>    ✗ [PATCH 1/1] cfi: Use rcu_read_{un}lock_sched_notrace
>      + Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com> (✓ DKIM/google.com)
>      + Signed-off-by: Kees Cook <keescook@...omium.org>
>      + Link: https://lore.kernel.org/r/20210811155914.19550-1-quic_eberman@quicinc.com
>    ---
>    ✗ BADSIG: DKIM/quicinc.com
> 
> 
> 
> Do you know if qualcomm is mangling outbound emails? (i.e. was the
> trailing body suffix added after calculating the DKIM signature?)

It's possible. I will check with our IT department. You may be aware 
that Qualcomm was previously using @codeaurora.org mails and this is my 
first time using new mail address.

I tried sending a patch to my personal Gmail address and it looked to be 
happy with the DKIM signature provided.

Please let me know if I should resend the patch a different way for you 
to be able to pull it in.

> 
> Thanks!
> 
> -Kees
>