Message-ID: <63dc0a89.170a0220.49507.0091@mx.google.com>
Date:   Thu, 2 Feb 2023 19:10:00 +0000
From:   Kees Cook <keescook@chromium.org>
To:     John Stultz <jstultz@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Ard Biesheuvel <ardb@kernel.org>
Cc:     Yongqin Liu <yongqin.liu@linaro.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Nishanth Menon <nm@ti.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Won Chung <wonchung@google.com>,
        David Gow <davidgow@google.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Andy Shevchenko <andriy.shevchenko@intel.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org,
        llvm@lists.linux.dev, Sumit Semwal <sumit.semwal@linaro.org>
Subject: Re: [PATCH 5/6] driver core: Add __alloc_size hint to devm allocators
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 <20221101223321.1326815-5-keescook@chromium.org>
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On Thu, Feb 02, 2023 at 10:56:29AM -0800, John Stultz wrote:
> That said, making sense of the error message isn't completely trivial
> either. I've been seeing a few cases recently of some of the new
> compiler tooling (I pinged you earlier on a CFI one) causing errors
> that developers aren't really sure how to address.  I know sometimes
> it's not easy to surface the errors with context to what was wrong,
> but at the risk of intense bike shedding, is there some way to provide
> something like "Likely array bounds error" instead of just "BRK
> handler: Fatal exception"?

Yeah, this is a result of the size trade-off that resulted in config
CONFIG_UBSAN_TRAP -- there ends up being no message about what went
wrong. I'd really like to have cleaner handling of this -- perhaps what
was done for KCFI could be applied to UBSAN as well, though this is an
area I don't know well myself. (i.e. encoding "this was a UBSAN trap"
in the trap itself.)

Sami or Ard, is this something that could be improved for arm64?

-- 
Kees Cook