On 10/02/2017 11:40 AM, Arnd Bergmann wrote: > The hardened strlen() function causes rather large stack usage > in at least one file in the kernel when CONFIG_KASAN is enabled: > > drivers/media/usb/em28xx/em28xx-dvb.c: In function 'em28xx_dvb_init': > drivers/media/usb/em28xx/em28xx-dvb.c:2062:1: error: the frame size of 3256 bytes is larger than 204 bytes [-Werror=frame-larger-than=] > > Analyzing this problem led to the discovery that gcc fails to > merge the stack slots for the i2c_board_info[] structures after > we strlcpy() into them, due to the 'noreturn' attribute on the > source string length check. > > The compiler behavior should get fixed in gcc-8, but for users > of existing gcc versions, we can work around it using an empty > inline assembly statement before the call to fortify_panic(). > > The workaround is unfortunately very ugly, and I tried my best > to limit it being applied to affected versions of gcc when > KASAN is used. Alternative suggestions welcome. > I don't have a really strong preference, so this approach is fine by me, but s/strlcpy/[strncpy|memcpy] approach seems a little better to me, because it's not ugly. This ugly workaround would make more sense if we a had lot of cases like in em28xx_dvb_init(). > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365 > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- > include/linux/string.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/include/linux/string.h b/include/linux/string.h > index c7a1132cdc93..1bf5ecdf8e01 100644 > --- a/include/linux/string.h > +++ b/include/linux/string.h > @@ -228,6 +228,16 @@ static inline const char *kbasename(const char *path) > #define __RENAME(x) __asm__(#x) > > void fortify_panic(const char *name) __noreturn __cold; > + > +/* work around GCC PR82365 */ > +#if defined(CONFIG_KASAN) && !defined(__clang__) && GCC_VERSION <= 80000 > +#define fortify_panic(x) \ > + do { \ > + asm volatile(""); \ > + fortify_panic(x); \ > + } while (0) > +#endif > + > void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter"); > void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter"); > void __read_overflow3(void) __compiletime_error("detected read beyond size of object passed as 3rd parameter"); > -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
