linux-kernel - Re: [PATCH 2/2] overflow, tracing: Define the is_signed

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Date:   Mon, 29 Aug 2022 12:30:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Isabella Basso <isabbasso@...eup.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sander Vanheule <sander@...nheule.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yury Norov <yury.norov@...il.com>
Subject: Re: [PATCH 2/2] overflow, tracing: Define the is_signed_type() macro
 once

On Fri, Aug 26, 2022 at 09:21:16AM -0700, Bart Van Assche wrote:
> There are two definitions of the is_signed_type() macro: one in
> <linux/overflow.h> and a second definition in <linux/trace_events.h>.
> 
> As suggested by Linus Torvalds, move the definition of the
> is_signed_type() macro into the <linux/compiler.h> header file. Change
> the definition of the is_signed_type() macro to make sure that it does
> not trigger any sparse warnings with future versions of sparse for
> bitwise types. See also:
> https://lore.kernel.org/all/CAHk-=whjH6p+qzwUdx5SOVVHjS3WvzJQr6mDUwhEyTf6pJWzaQ@mail.gmail.com/
> https://lore.kernel.org/all/CAHk-=wjQGnVfb4jehFR0XyZikdQvCZouE96xR_nnf5kqaM5qqQ@mail.gmail.com/
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Isabella Basso <isabbasso@...eup.net>
> Cc: "Jason A. Donenfeld" <Jason@...c4.com>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: Luc Van Oostenryck <luc.vanoostenryck@...il.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> Cc: Sander Vanheule <sander@...nheule.net>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Yury Norov <yury.norov@...il.com>
> Signed-off-by: Bart Van Assche <bvanassche@....org>
> ---
>  include/linux/compiler.h     | 6 ++++++
>  include/linux/overflow.h     | 1 -
>  include/linux/trace_events.h | 2 --
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 01ce94b58b42..7713d7bcdaea 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -239,6 +239,12 @@ static inline void *offset_to_ptr(const int *off)
>  /* &a[0] degrades to a pointer: a different type from an array */
>  #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
>  
> +/*
> + * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
> + * bool and also pointer types.
> + */
> +#define is_signed_type(type) (((type)(-1)) < (__force type)1)
> +
>  /*
>   * This is needed in functions which generate the stack canary, see
>   * arch/x86/kernel/smpboot.c::start_secondary() for an example.
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index f1221d11f8e5..0eb3b192f07a 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -30,7 +30,6 @@
>   * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
>   * credit to Christian Biere.
>   */
> -#define is_signed_type(type)       (((type)(-1)) < (type)1)
>  #define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
>  #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
>  #define type_min(T) ((T)((T)-type_max(T)-(T)1))
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index b18759a673c6..8401dec93c15 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -814,8 +814,6 @@ extern int trace_add_event_call(struct trace_event_call *call);
>  extern int trace_remove_event_call(struct trace_event_call *call);
>  extern int trace_event_get_offsets(struct trace_event_call *call);
>  
> -#define is_signed_type(type)	(((type)(-1)) < (type)1)
> -
>  int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set);
>  int trace_set_clr_event(const char *system, const char *event, int set);
>  int trace_array_set_clr_event(struct trace_array *tr, const char *system,

Yeah, this looks good. I'll take these as part of the hardening tree
since it's touching overflow.h, unless I hear otherwise. :)

-- 
Kees Cook