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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Thu, 2 Feb 2023 12:11:47 -0800
Message-ID: <CABCJKueSasiWQvO2jZ-8KUF+c-dNgf87pR45sfHHCQMyyTvL0Q@mail.gmail.com>
Subject: Re: [PATCH 5/6] driver core: Add __alloc_size hint to devm allocators
To:     Kees Cook <keescook@chromium.org>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        John Stultz <jstultz@google.com>,
        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>,
        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>
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On Thu, Feb 2, 2023 at 11:53 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Feb 02, 2023 at 11:49:42AM -0800, Sami Tolvanen wrote:
> > A quick look at Clang's source code suggests that Intrinsic::ubsantrap
> > already accepts the handler ID (from the SanitizerHandler enum) as an
> > argument and the arm64 LLVM back-end appears to encode the value as an
> > immediate for the brk instruction. I didn't confirm that this actually
> > works, but perhaps we just need to teach the kernel about the possible
> > values?
>
> Oh excellent. Yeah, if that's all that's needed here that would be
> great. What are the values?

The arm64 brk immediate encoding seems to be "ubsantrap arg | 'U' << 8":

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64InstrInfo.td#L7571

The argument values come from the SanitizerHandler enum, which is
populated from this list:

https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenFunction.h#L113

Therefore, according to the tests, for ubsantrap(12) we'll get brk
#0x550c, for example:

https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/AArch64/ubsantrap.ll

Sami