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SubjectRe: [PATCH 7/7] bug: Move WARN_ON() "cut here" into exception handler
On Tue, Aug 20, 2019 at 12:58:49PM +0200, Christophe Leroy wrote:
> Le 20/08/2019 à 12:06, Peter Zijlstra a écrit :
> > On Mon, Aug 19, 2019 at 04:41:11PM -0700, Kees Cook wrote:
> >
> > > diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> > > index 588dd59a5b72..da471fcc5487 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_PRINTK (1 << 3)
> > > #define BUGFLAG_TAINT(taint) ((taint) << 8)
> > > #define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
> > > #endif
> >
> > > diff --git a/lib/bug.c b/lib/bug.c
> > > index 1077366f496b..6c22e8a6f9de 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_PRINTK) == 0)
> > > + printk(KERN_DEFAULT CUT_HERE);
> >
> > I'm not loving that BUGFLAG_PRINTK name, BUGFLAG_CUT_HERE makes more
> > sense to me.

That's fine -- easy rename. :)

> Actually it would be BUGFLAG_NO_CUT_HERE then, otherwise all arches not
> using the generic macros will have to add the flag to get the "cut here"
> line.

I am testing for the lack of the flag (so that only the
CONFIG_GENERIC_BUG with __WARN_FLAGS case needs to set it). I was
thinking of the flag to mean "this reporting flow has already issued
cut-here". It sounds like it would be more logical to have it named
BUGFLAG_NO_CUT_HERE to mean "do not issue a cut-here; it has already
happened"? I will update the patch.

Thanks!

--
Kees Cook

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