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Message-ID: <20200615161738.18d07ce6@oasis.local.home>
Date: Mon, 15 Jun 2020 16:17:38 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Oscar Carter <oscar.carter@....com>
Cc: Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/trace: Remove function callback casts
On Sun, 14 Jun 2020 09:01:54 +0200
Oscar Carter <oscar.carter@....com> wrote:
> In an effort to enable -Wcast-function-type in the top-level Makefile to
> support Control Flow Integrity builds, remove all the function callback
> casts.
>
> To do this, use the ftrace_ops_list_func function as a wrapper when the
> arch not supports ftrace ops instead of the use of a function cast.
>
We need more tricker than this.
> Signed-off-by: Oscar Carter <oscar.carter@....com>
> ---
> kernel/trace/ftrace.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c163c3531faf..ed1efc0e3a25 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -119,13 +119,12 @@ struct ftrace_ops __rcu *ftrace_ops_list __read_mostly = &ftrace_list_end;
> ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
> struct ftrace_ops global_ops;
>
> -#if ARCH_SUPPORTS_FTRACE_OPS
> static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *op, struct pt_regs *regs);
> -#else
> +
> +#if !ARCH_SUPPORTS_FTRACE_OPS
> /* See comment below, where ftrace_ops_list_func is defined */
> static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
> -#define ftrace_ops_list_func ((ftrace_func_t)ftrace_ops_no_ops)
The reason for the typecast is because this gets called from asm with only two parameters.
> #endif
>
> static inline void ftrace_ops_init(struct ftrace_ops *ops)
> @@ -6860,6 +6859,12 @@ static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> }
> NOKPROBE_SYMBOL(ftrace_ops_list_func);
> #else
> +static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *op, struct pt_regs *regs)
> +{
> + ftrace_ops_no_ops(ip, parent_ip);
> +}
> +
> static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip)
> {
> __ftrace_ops_list_func(ip, parent_ip, NULL, NULL);
> --
> 2.20.1
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