linux-kernel - Re: linux-next: Tree for Mar 18 (objtool)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <202003201131.9B688BC@keescook>
Date:   Fri, 20 Mar 2020 11:35:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: Tree for Mar 18 (objtool)

On Fri, Mar 20, 2020 at 09:26:13AM +0100, Peter Zijlstra wrote:
> On Thu, Mar 19, 2020 at 12:45:50PM -0500, Josh Poimboeuf wrote:
> > > On Thu, Mar 19, 2020 at 12:33:31PM -0500, Josh Poimboeuf wrote:
> 
> > > > Actually I suspect it's the __builtin_unreachable() annotation which is
> > > > making UBSAN add the __builtin_trap()...  because I don't see any double
> > > > UD2s for WARNs.
> 
> > Actually, removing __builtin_unreachable() *does* make the extra UD2 go
> > away -- I forgot I had some silly debug code.
> 
> LOL, check this:
> 
> "Built-in Function: void __builtin_unreachable (void)
> 
>     If control flow reaches the point of the __builtin_unreachable, the
>     program is undefined. It is useful in situations where the compiler
>     cannot deduce the unreachability of the code. "
> 
> Which, I bet, is what makes UBSAN insert that __builtin_trap().
> 
> What a friggin mess :/

What I'd like is to be able to specify to UBSAN what function to call
for the trap. I'd prefer to specify a well-defined exception handler,
but at present, UBSAN just inserts __builtin_trap().

Can't objtool be told to ignore a ud2 that lacks an execution path to it?

-- 
Kees Cook