On Thu, Aug 27, 2020 at 10:55:32AM -0700, Linus Torvalds wrote:
> On Thu, Aug 27, 2020 at 10:34 AM Linus Torvalds
> <torva...@linux-foundation.org> wrote:
> >
> > How are you guys testing? I have UBSAN and GCOV on, and don't see
> > crazy frames on either i386 or x86-64.
>
> Oh, never mind. I also have COMPILE_TEST on, so it ends up disabling
> GCOV_PROFILE_ALL and UBSAN_SANITIZE_ALL.
>
> And yeah, this seems to be a gcc bug. It generates a ton of stack
> slots for temporaries. It's -fsanitize=object-size that seems to do
> it.
>
> And "-fstack-reuse=all" doesn't seem to make any difference.
>
> So I think
>
> (a) our stack size check is good to catch this
>
> (b) gcc and -fsanitize=object-size is basically an unusable combination
>
> and it's not a bug in the kernel.
Do you mean you checked both gcc and clang and it was only a problem with gcc?
(If so, I can tweak the "depends" below...)
This should let us avoid it, I'm currently testing:
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 774315de555a..24091315c251 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -47,6 +47,19 @@ config UBSAN_BOUNDS
to the {str,mem}*cpy() family of functions (that is addressed
by CONFIG_FORTIFY_SOURCE).
+config UBSAN_OBJECT_SIZE
+ bool "Check for accesses beyond known object sizes"
+ default UBSAN
+ depends on !COMPILE_TEST
+ help
+ This option enables detection of cases where accesses may
+ happen beyond the end of an object's size, which happens in
+ places like invalid downcasts, or calling function pointers
+ through invalid pointers.
+
+ This uses much more stack space, and isn't recommended for
+ cases were stack utilization depth is a concern.
+
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..3ff67e9b17fd 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -7,12 +7,15 @@ ifdef CONFIG_UBSAN_BOUNDS
CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
endif
+ifdef CONFIG_UBSAN_OBJECT_SIZE
+ CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
+endif
+
ifdef CONFIG_UBSAN_MISC
CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow)
- CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum)
endif
--
Kees Cook
