linux-hardening - Re: [GIT PULL] Block fixes for 6.3-rc3

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Date:   Fri, 17 Mar 2023 15:56:16 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Jens Axboe <axboe@...nel.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        linux-hardening@...r.kernel.org
Subject: Re: [GIT PULL] Block fixes for 6.3-rc3

On Fri, Mar 17, 2023 at 2:00 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Fri, Mar 17, 2023 at 1:51 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > but I would *really* like clang to be fixed to not silently generate
> > code that does insane things and would be basically impossible to
> > debug if it ever triggers.
>
> Side note: the key word here is "silently".
>
> If clang notices that it generates crazy code, a warning at build-time
> would be preferable to the "oh, we noticed the crazy code generation
> because we do sanity checking that just happened to catch it".

That's fair.  I have something hacked up locally that can spot the
fallthough from m5mols_set_fmt() as objtool did. With some polish, we
can likely ship that as a compiler warning.  Then we can have these
checks regardless of objtool arch support.

First I need to teach LLVM that __stack_chk_fail is noreturn, though
I've only verified that thus far in glibc, musl, and bionic; I still
need to check that's the case for the BSDs' libcs.
-- 
Thanks,
~Nick Desaulniers