Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <c01cb530-a937-4eba-92d0-0e7cc497929e@kernel.dk>
Date:   Wed, 10 Aug 2022 19:06:00 -0600
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101
 Thunderbird/91.10.0
Subject: Re: [PATCH v2 0/2] link with -z noexecstack --no-warn-rwx-segments
Content-Language: en-US
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Fangrui Song <maskray@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nick Clifton <nickc@redhat.com>, brijesh.singh@amd.com,
        hpa@zytor.com, kirill.shutemov@linux.intel.com,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        michael.roth@amd.com, n.schier@avm.de, nathan@kernel.org,
        sathyanarayanan.kuppuswamy@linux.intel.com, trix@redhat.com,
        x86@kernel.org
References: <20220809013653.xtmeekefwkbo46vk@google.com>
 <20220810222442.2296651-1-ndesaulniers@google.com>
 <20220810222442.2296651-3-ndesaulniers@google.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <20220810222442.2296651-3-ndesaulniers@google.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 8/10/22 4:24 PM, Nick Desaulniers wrote:
> Users of GNU ld (BFD) from binutils 2.39+ will observe multiple
> instances of a new warning when linking kernels in the form:
> 
>   ld: warning: vmlinux: missing .note.GNU-stack
>   section implies executable stack
>   ld: NOTE: This behaviour is deprecated and will be removed in a future
>   version of the linker
>   ld: warning: vmlinux has a LOAD segment with RWX permissions
> 
> Generally, we would like to avoid the stack being executable. Because
> there could be a need for the stack to be executable, assembler sources
> have to opt-in to this security feature via explicit creation of the
> .note.GNU-stack feature (which compilers create by default) or command
> line flag --noexecstack. Or we can simply tell the linker the production
> of such sections is irrelevant and to link the stack as --noexecstack.
> 
> LLVM's LLD linker defaults to -z noexecstack, so this flag isn't
> strictly necessary when linking with LLD, only BFD, but it doesn't hurt
> to be explicit here for all linkers IMO. --no-warn-rwx-segments is
> currently BFD specific and only available in the current latest release,
> so it's wrapped in an ld-option check.
> 
> While the kernel makes extensive usage of ELF sections, it doesn't use
> permissions from ELF segments.
> 
> Broken up into 2 patches; one for the top level vmlinux, one x86
> specific since a few places in the x86 build reset KBUILD_LDFLAGS.

For x86-64:

Tested-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe