linux-kernel - Re: [PATCH v4 05/15] tracepoint: Exclude tp_stub

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Message-ID: <CAKwvOdnJ6EPPd5UbhZhdggPRzCXmdrnxg_tO=Bq_+Gcgarvw1g@mail.gmail.com>
Date:   Thu, 30 Sep 2021 11:50:57 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     x86@...nel.org, Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v4 05/15] tracepoint: Exclude tp_stub_func from CFI checking

On Thu, Sep 30, 2021 at 11:05 AM Sami Tolvanen <samitolvanen@...gle.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@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  kernel/tracepoint.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 64ea283f2f86..58acc7d86c3f 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c

looking at 4+5/15 together, I wonder if this TU should explicitly
include linux/cfi.h?

> @@ -99,10 +99,7 @@ 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);
>
>  static inline void *allocate_probes(int count)
>  {
> --
> 2.33.0.800.g4c38ced690-goog
>


-- 
Thanks,
~Nick Desaulniers