On Mon, Dec 16, 2019 at 10:26:56AM +0000, Will Deacon wrote: > Hi Kees, > > On Thu, Nov 21, 2019 at 10:15:17AM -0800, Kees Cook wrote: > > The Undefined Behavior Sanitizer can operate in two modes: warning > > reporting mode via lib/ubsan.c handler calls, or trap mode, which uses > > __builtin_trap() as the handler. Using lib/ubsan.c means the kernel > > image is about 5% larger (due to all the debugging text and reporting > > structures to capture details about the warning conditions). Using the > > trap mode, the image size changes are much smaller, though at the loss > > of the "warning only" mode. > > > > In order to give greater flexibility to system builders that want > > minimal changes to image size and are prepared to deal with kernel code > > being aborted and potentially destabilizing the system, this introduces > > CONFIG_UBSAN_TRAP. The resulting image sizes comparison: > > > > text data bss dec hex filename > > 19533663 6183037 18554956 44271656 2a38828 vmlinux.stock > > 19991849 7618513 18874448 46484810 2c54d4a vmlinux.ubsan > > 19712181 6284181 18366540 44362902 2a4ec96 vmlinux.ubsan-trap > > > > CONFIG_UBSAN=y: image +4.8% (text +2.3%, data +18.9%) > > CONFIG_UBSAN_TRAP=y: image +0.2% (text +0.9%, data +1.6%) > > > > Additionally adjusts the CONFIG_UBSAN Kconfig help for clarity and > > removes the mention of non-existing boot param "ubsan_handle". > > > > Suggested-by: Elena Petrova <lenaptr@xxxxxxxxxx> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > lib/Kconfig.ubsan | 22 ++++++++++++++++++---- > > lib/Makefile | 2 ++ > > scripts/Makefile.ubsan | 9 +++++++-- > > 3 files changed, 27 insertions(+), 6 deletions(-) > > > > diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan > > index 0e04fcb3ab3d..9deb655838b0 100644 > > --- a/lib/Kconfig.ubsan > > +++ b/lib/Kconfig.ubsan > > @@ -5,11 +5,25 @@ config ARCH_HAS_UBSAN_SANITIZE_ALL > > config UBSAN > > bool "Undefined behaviour sanity checker" > > help > > - This option enables undefined behaviour sanity checker > > + This option enables the Undefined Behaviour sanity checker. > > Compile-time instrumentation is used to detect various undefined > > - behaviours in runtime. Various types of checks may be enabled > > - via boot parameter ubsan_handle > > - (see: Documentation/dev-tools/ubsan.rst). > > + behaviours at runtime. For more details, see: > > + Documentation/dev-tools/ubsan.rst > > + > > +config UBSAN_TRAP > > + bool "On Sanitizer warnings, abort the running kernel code" > > + depends on UBSAN > > + depends on $(cc-option, -fsanitize-undefined-trap-on-error) > > + help > > + Building kernels with Sanitizer features enabled tends to grow > > + the kernel size by around 5%, due to adding all the debugging > > + text on failure paths. To avoid this, Sanitizer instrumentation > > + can just issue a trap. This reduces the kernel size overhead but > > + turns all warnings (including potentially harmless conditions) > > + into full exceptions that abort the running kernel code > > + (regardless of context, locks held, etc), which may destabilize > > + the system. For some system builders this is an acceptable > > + trade-off. > > Slight nit, but I wonder if it would make sense to move all this under a > 'menuconfig UBSAN' entry, so the dependencies can be dropped? Then you could > have all of the suboptions default to on and basically choose which > individual compiler options to disable based on your own preferences. Sure; I can do that. I'll respin the series. -- Kees Cook
