On Thu, Sep 17, 2020 at 08:37:07AM +0200, Marco Elver wrote: > On Wed, 16 Sep 2020 at 15:40, Marco Elver <elver@xxxxxxxxxx> wrote: > > On Wed, Sep 16, 2020 at 12:14PM +0000, George Popescu wrote: > > > On Wed, Sep 16, 2020 at 10:32:40AM +0200, Marco Elver wrote: > > > > On Wed, 16 Sep 2020 at 09:40, George Popescu <georgepope@xxxxxxxxxx> wrote: > > > > > On Tue, Sep 15, 2020 at 07:32:28PM +0200, Marco Elver wrote: > > > > > > On Tue, 15 Sep 2020 at 14:01, George Popescu <georgepope@xxxxxxxxxx> wrote: > > > > > > > On Tue, Sep 15, 2020 at 01:18:11PM +0200, Marco Elver wrote: > > > > > > > > On Tue, 15 Sep 2020 at 12:25, George Popescu <georgepope@xxxxxxxxxx> wrote: > > > > > > > > > On Mon, Sep 14, 2020 at 03:13:14PM -0700, Kees Cook wrote: > > > > > > > > > > On Mon, Sep 14, 2020 at 05:27:42PM +0000, George-Aurelian Popescu wrote: > > > > > > > > > > > From: George Popescu <georgepope@xxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > When the kernel is compiled with Clang, UBSAN_BOUNDS inserts a brk after > > > > > > > > > > > the handler call, preventing it from printing any information processed > > > > > > > > > > > inside the buffer. > > > > > > > > > > > For Clang -fsanitize=bounds expands to -fsanitize=array-bounds and > > > > > > > > > > > -fsanitize=local-bounds, and the latter adds a brk after the handler > > > > > > > > > > > call > > > > > > > > > > > > > > > > > > > This would mean losing the local-bounds coverage. I tried to test it without > > > > > > > > > local-bounds and with a locally defined array on the stack and it works fine > > > > > > > > > (the handler is called and the error reported). For me it feels like > > > > > > > > > --array-bounds and --local-bounds are triggered for the same type of > > > > > > > > > undefined_behaviours but they are handling them different. > > > > > > > > > > > > > > > > Does -fno-sanitize-trap=bounds help? > > [...] > > > > Your full config would be good, because it includes compiler version etc. > > > My full config is: > > > > Thanks. Yes, I can reproduce, and the longer I keep digging I start > > wondering why we have local-bounds at all. > > > > It appears that local-bounds finds a tiny subset of the issues that > > KASAN finds: > > > > http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20131021/091536.html > > http://llvm.org/viewvc/llvm-project?view=revision&revision=193205 > > > > fsanitize=undefined also does not include local-bounds: > > > > https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#available-checks > > > > And the reason is that we do want to enable KASAN and UBSAN together; > > but local-bounds is useless overhead if we already have KASAN. > > > > I'm inclined to say that what you propose is reasonable (but the commit > > message needs to be more detailed explaining the relationship with > > KASAN) -- but I have no idea if this is going to break somebody's > > usecase (e.g. find some OOB bugs, but without KASAN -- but then why not > > use KASAN?!) > > So, it seems that local-bounds can still catch some rare OOB accesses, > where KASAN fails to catch it because the access might skip over the > redzone. > > The other more interesting bit of history is that > -fsanitize=local-bounds used to be -fbounds-checking, and meant for > production use as a hardening feature: > http://lists.llvm.org/pipermail/llvm-dev/2012-May/049972.html > > And local-bounds just does not behave like any other sanitizer as a > result, it just traps. The fact that it's enabled via > -fsanitize=local-bounds (or just bounds) but hasn't much changed in > behaviour is a little unfortunate. > I suppose there are 3 options: > > 1. George implements trap handling somehow. Is this feasible? If not, > why not? Maybe that should also have been explained in the commit > message. > > 2. Only enable -fsanitize=local-bounds if UBSAN_TRAP was selected, at > least for as long as Clang traps for local-bounds. I think this makes > sense either way, because if we do not expect UBSAN to trap, it really > should not trap! > > 3. Change the compiler. As always, this will take a while to implement > and then to reach whoever should have that updated compiler. > > Preferences? Considering of what you said above, I find option 2 the most elegant. The first one doesn't sound doable for the moment, also the third. I will edit this patch considering your comments and resend it to the list. Thank you for your support. Thanks, George
