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Date:   Mon, 17 Jan 2022 17:54:14 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Mark Brown <broonie@kernel.org>
Cc:     Jeremy Linton <jeremy.linton@arm.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        Will Deacon <will@kernel.org>,
        "H . J . Lu" <hjl.tools@gmail.com>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        libc-alpha@sourceware.org, Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v7 0/4] arm64: Enable BTI for the executable as well as
 the interpreter
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On Fri, Jan 07, 2022 at 12:01:17PM +0000, Catalin Marinas wrote:
> I think we can look at this from two angles:
> 
> 1. Ignoring MDWE, should whoever does the original mmap() also honour
>    PROT_BTI? We do this for static binaries but, for consistency, should
>    we extend it to dynamic executable?
> 
> 2. A 'simple' fix to allow MDWE together with BTI.

Thinking about it, (1) is not that different from the kernel setting
PROT_EXEC on the main executable when the dynamic loader could've done
it as well. There is a case for making this more consistent: whoever
does the mmap() should use the full attributes.

Question for the toolchain people: would the compiler ever generate
relocations in the main executable that the linker needs to resolve via
an mprotect(READ|WRITE) followed by mprotect(READ|EXEC)? If yes, we'd
better go for a proper MDWE implementation in the kernel.

-- 
Catalin