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

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Message-ID: <202108111306.527943F39@keescook>
Date:   Wed, 11 Aug 2021 13:10:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, Jinlong Mao <jinlmao@...eaurora.org>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>
Subject: Re: [PATCH 1/1] cfi: Use rcu_read_{un}lock_sched_notrace

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?)

Thanks!

-Kees

-- 
Kees Cook