lkml.org 
[lkml]   [2019]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception handler
From
Date
In-Reply-To: 20190819234111.9019-8-keescook@chromium.org

Le 20/08/2019 à 18:47, Kees Cook a écrit :
> The original clean up of "cut here" missed the WARN_ON() case (that
> does not have a printk message), which was fixed recently by adding
> an explicit printk of "cut here". This had the downside of adding a
> printk() to every WARN_ON() caller, which reduces the utility of using
> an instruction exception to streamline the resulting code. By making
> this a new BUGFLAG, all of these can be removed and "cut here" can be
> handled by the exception handler.
>
> This was very pronounced on PowerPC, but the effect can be seen on
> x86 as well. The resulting text size of a defconfig build shows some
> small savings from this patch:
>
> text data bss dec hex filename
> 19691167 5134320 1646664 26472151 193eed7 vmlinux.before
> 19676362 5134260 1663048 26473670 193f4c6 vmlinux.after
>
> This change also opens the door for creating something like BUG_MSG(),
> where a custom printk() before issuing BUG(), without confusing the "cut
> here" line.
>
> Reported-by: Christophe Leroy <christophe.leroy@c-s.fr>
> Fixes: Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
> Signed-off-by: Kees Cook <keescook@chromium.org>

Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>

> ---
> v2:
> - rename BUGFLAG_PRINTK to BUGFLAG_NO_CUT_HERE (peterz, christophe)
> ---
> include/asm-generic/bug.h | 8 +++-----
> lib/bug.c | 11 +++++++++--
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index 588dd59a5b72..a21e83f8a274 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -10,6 +10,7 @@
> #define BUGFLAG_WARNING (1 << 0)
> #define BUGFLAG_ONCE (1 << 1)
> #define BUGFLAG_DONE (1 << 2)
> +#define BUGFLAG_NO_CUT_HERE (1 << 3) /* CUT_HERE already sent */
> #define BUGFLAG_TAINT(taint) ((taint) << 8)
> #define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
> #endif
> @@ -86,13 +87,10 @@ void warn_slowpath_fmt(const char *file, const int line, unsigned taint,
> warn_slowpath_fmt(__FILE__, __LINE__, taint, arg)
> #else
> extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
> -#define __WARN() do { \
> - printk(KERN_WARNING CUT_HERE); \
> - __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN)); \
> - } while (0)
> +#define __WARN() __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
> #define __WARN_printf(taint, arg...) do { \
> __warn_printk(arg); \
> - __WARN_FLAGS(BUGFLAG_TAINT(taint)); \
> + __WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
> } while (0)
> #define WARN_ON_ONCE(condition) ({ \
> int __ret_warn_on = !!(condition); \
> diff --git a/lib/bug.c b/lib/bug.c
> index 1077366f496b..8c98af0bf585 100644
> --- a/lib/bug.c
> +++ b/lib/bug.c
> @@ -181,6 +181,15 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
> }
> }
>
> + /*
> + * BUG() and WARN_ON() families don't print a custom debug message
> + * before triggering the exception handler, so we must add the
> + * "cut here" line now. WARN() issues its own "cut here" before the
> + * extra debugging message it writes before triggering the handler.
> + */
> + if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
> + printk(KERN_DEFAULT CUT_HERE);
> +
> if (warning) {
> /* this is a WARN_ON rather than BUG/BUG_ON */
> __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
> @@ -188,8 +197,6 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
> return BUG_TRAP_TYPE_WARN;
> }
>
> - printk(KERN_DEFAULT CUT_HERE);
> -
> if (file)
> pr_crit("kernel BUG at %s:%u!\n", file, line);
> else
>

\
 
 \ /
  Last update: 2019-08-23 16:57    [W:0.126 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site