Re: [PATCH v3] ubsan: introducing CONFIG_UBSAN_LOCAL_BOUNDS for Clang

[Marco Elver]

On Fri, 2 Oct 2020 at 16:43, George Popescu <georgepope@xxxxxxxxxx> wrote:
>
> Is this patch ready to be merged?

Andrew already picked this up and it's in the -mm tree:
https://lore.kernel.org/mm-commits/20200922170717.qhs0j%25akpm@xxxxxxxxxxxxxxxxxxxx/

You have to wait for the next merge window, which will likely start in
1.5 weeks (or, on Monday, but unlikely:
https://lwn.net/Articles/832733/).

Thanks,
-- Marco

> Best regards,
> George
>
>
> On Tue, Sep 22, 2020 at 10:43 AM George-Aurelian Popescu
> <georgepope@xxxxxxxxxx> wrote:
> >
> > From: George Popescu <georgepope@xxxxxxxxxxx>
> >
> > When the kernel is compiled with Clang, -fsanitize=bounds expands to
> > -fsanitize=array-bounds and -fsanitize=local-bounds.
> >
> > Enabling -fsanitize=local-bounds with Clang has the unfortunate
> > side-effect of inserting traps; this goes back to its original intent,
> > which was as a hardening and not a debugging feature [1]. The same feature
> > made its way into -fsanitize=bounds, but the traps remained. For that
> > reason, -fsanitize=bounds was split into 'array-bounds' and
> > 'local-bounds' [2].
> >
> > Since 'local-bounds' doesn't behave like a normal sanitizer, enable
> > it with Clang only if trapping behaviour was requested by
> > CONFIG_UBSAN_TRAP=y.
> >
> > Add the UBSAN_BOUNDS_LOCAL config to Kconfig.ubsan to enable the
> > 'local-bounds' option by default when UBSAN_TRAP is enabled.
> >
> > [1] http://lists.llvm.org/pipermail/llvm-dev/2012-May/049972.html
> > [2] http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20131021/091536.html
> >
> > Suggested-by: Marco Elver <elver@xxxxxxxxxx>
> > Reviewed-by: David Brazdil <dbrazdil@xxxxxxxxxx>
> > Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> > Signed-off-by: George Popescu <georgepope@xxxxxxxxxxx>
> >
> > ---
> > v2: changed the name of the config, in Kconfig, to UBSAN_LOCAL_BOUNDS
> > ---
> > v3: added Reviewed-by tag
> > ---
> >  lib/Kconfig.ubsan      | 14 ++++++++++++++
> >  scripts/Makefile.ubsan | 10 +++++++++-
> >  2 files changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> > index 774315de555a..58f8d03d037b 100644
> > --- a/lib/Kconfig.ubsan
> > +++ b/lib/Kconfig.ubsan
> > @@ -47,6 +47,20 @@ config UBSAN_BOUNDS
> >           to the {str,mem}*cpy() family of functions (that is addressed
> >           by CONFIG_FORTIFY_SOURCE).
> >
> > +config UBSAN_LOCAL_BOUNDS
> > +       bool "Perform array local bounds checking"
> > +       depends on UBSAN_TRAP
> > +       depends on CC_IS_CLANG
> > +       depends on !UBSAN_KCOV_BROKEN
> > +       help
> > +         This option enables -fsanitize=local-bounds which traps when an
> > +         exception/error is detected. Therefore, it should be enabled only
> > +         if trapping is expected.
> > +         Enabling this option detects errors due to accesses through a
> > +         pointer that is derived from an object of a statically-known size,
> > +         where an added offset (which may not be known statically) is
> > +         out-of-bounds.
> > +
> >  config UBSAN_MISC
> >         bool "Enable all other Undefined Behavior sanity checks"
> >         default UBSAN
> > diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> > index 27348029b2b8..4e3fff0745e8 100644
> > --- a/scripts/Makefile.ubsan
> > +++ b/scripts/Makefile.ubsan
> > @@ -4,7 +4,15 @@ ifdef CONFIG_UBSAN_ALIGNMENT
> >  endif
> >
> >  ifdef CONFIG_UBSAN_BOUNDS
> > -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> > +      ifdef CONFIG_CC_IS_CLANG
> > +            CFLAGS_UBSAN += -fsanitize=array-bounds
> > +      else
> > +            CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> > +      endif
> > +endif
> > +
> > +ifdef CONFIG_UBSAN_LOCAL_BOUNDS
> > +      CFLAGS_UBSAN += -fsanitize=local-bounds
> >  endif
> >
> >  ifdef CONFIG_UBSAN_MISC
> > --
> > 2.28.0.681.g6f77f65b4e-goog
> >