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Date:   Wed, 13 Oct 2021 15:20:07 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     x86@kernel.org, Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Subject: Re: [PATCH v5 05/15] tracepoint: Exclude tp_stub_func from CFI
 checking
Message-ID: <20211013152007.7b2e57f4@gandalf.local.home>
In-Reply-To: <20211013181658.1020262-6-samitolvanen@google.com>
References: <20211013181658.1020262-1-samitolvanen@google.com>
        <20211013181658.1020262-6-samitolvanen@google.com>
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On Wed, 13 Oct 2021 11:16:48 -0700
Sami Tolvanen <samitolvanen@google.com> wrote:

> If allocate_probes fails, func_remove replaces the old function
> with a pointer to tp_stub_func, which is called using a mismatching
> function pointer that will always trip indirect call checks with
> CONFIG_CFI_CLANG. Use DEFINE_CFI_IMMEDATE_RETURN_STUB to define
> tp_stub_func to allow it to pass CFI checking.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> ---
>  kernel/tracepoint.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 64ea283f2f86..8a0d463c8507 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -9,6 +9,7 @@
>  #include <linux/list.h>
>  #include <linux/rcupdate.h>
>  #include <linux/tracepoint.h>
> +#include <linux/cfi.h>
>  #include <linux/err.h>
>  #include <linux/slab.h>
>  #include <linux/sched/signal.h>
> @@ -99,10 +100,7 @@ struct tp_probes {
>  };
>  
>  /* Called in removal of a func but failed to allocate a new tp_funcs */
> -static void tp_stub_func(void)
> -{
> -	return;
> -}
> +static DEFINE_CFI_IMMEDIATE_RETURN_STUB(tp_stub_func);

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

>  
>  static inline void *allocate_probes(int count)
>  {