Re: [PATCH 1/1] cfi: Use rcu_read_{un}lock_sched_notrace

[Elliot Berman]

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@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx/raw
> (DKIM_INVALID)
>
> $ b4 am -tls https://lore.kernel.org/lkml/20210811155914.19550-1-quic_eberman@xxxxxxxxxxx/
> 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@xxxxxxxxxx> (✓ DKIM/google.com)
>      + Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>      + Link: https://lore.kernel.org/r/20210811155914.19550-1-quic_eberman@xxxxxxxxxxx
>    ---
>    ✗ 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