linux-hardening - Re: [PATCH 1/4] Compiler Attributes: Add Clang's __pass_object

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Date:   Wed, 2 Feb 2022 02:11:51 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev,
        George Burgess IV <gbiv@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 1/4] Compiler Attributes: Add Clang's __pass_object_size

On Wed, Feb 2, 2022 at 1:30 AM Kees Cook <keescook@...omium.org> wrote:
>
> +/*
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size

For attributes that are not supported under all compilers, we have the
"Optional" lines in the comment. From a quick look in Godbolt,
`__pass_object_size__` and `__overloadable__` are supported for all
Clang >= 11 but not GCC/ICC. Thus, could you please add to the
comment:

    * Optional: not supported by gcc.
    * Optional: not supported by icc.

to those two patches?

For `__diagnose_as_builtin__`, I only see it on Clang trunk, so I
assume >= 14, thus could you please add:

    * Optional: only supported since clang >= 14.

?

Thanks!

> + * The "type" argument should match the __builtin_object_size(p, type) usage.

This should go above on top of the comment (it is true there is one
case that does not follow it, but that one has to be cleaned up).

Also, this bit seems to be explained in the Clang documentation (i.e.
not kernel-specific). Do you think we need it here?

Cheers,
Miguel