linux-kernel - Re: [PATCH] fs: Preventing READ_IMPLIES

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Date:   Tue, 18 Apr 2017 21:01:52 +0100
From:   Peter Maydell <peter.maydell@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     "dongbo (E)" <dongbo4@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Maydell <Peter.Maydell@....com>,
        Will Deacon <will.deacon@....com>,
        Linuxarm <linuxarm@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] fs: Preventing READ_IMPLIES_EXEC Propagation

On 18 April 2017 at 18:01, Catalin Marinas <catalin.marinas@....com> wrote:
> On Thu, Apr 13, 2017 at 08:33:52PM +0800, dongbo (E) wrote:
>> From: Dong Bo <dongbo4@...wei.com>
>>
>> In load_elf_binary(), once the READ_IMPLIES_EXEC flag is set,
>> the flag is propagated to its child processes, even the elf
>> files are marked as not requiring executable stack. It may
>> cause superfluous operations on some arch, e.g.
>> __sync_icache_dcache on aarch64 due to a PROT_READ mmap is
>> also marked as PROT_EXEC.

> That's affecting most architectures with a risk of ABI breakage. We
> could do it on arm64 only, though I'm not yet clear on the ABI
> implications (at a first look, there shouldn't be any).

Is there a reason why it isn't just straightforwardly a bug
(which we could fix) to make READ_IMPLIES_EXEC propagate to
child processes? AFAICT this should be per-process: just because
init happens not to have been (re)compiled to permit non-executable
stacks doesn't mean every process on the system needs to have
an executable stack. Behaviour shouldn't be variable across
architectures either, I would hope.

thanks
-- PMM