linux-kernel - Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures

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Date:   Fri, 23 Oct 2020 10:02:32 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Topi Miettinen <toiwoton@...il.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Jeremy Linton <jeremy.linton@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, libc-alpha@...rceware.org,
        systemd-devel@...ts.freedesktop.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Dave Martin <dave.martin@....com>,
        Will Deacon <will.deacon@....com>,
        Salvatore Mesoraca <s.mesoraca16@...il.com>,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org
Subject: Re: BTI interaction between seccomp filters in systemd and glibc
 mprotect calls, causing service failures

On Thu, Oct 22, 2020 at 01:02:18PM -0700, Kees Cook wrote:
> Regardless, it makes sense to me to have the kernel load the executable
> itself with BTI enabled by default. I prefer gaining Catalin's suggested
> patch[2]. :)
[...]
> [2] https://lore.kernel.org/linux-arm-kernel/20201022093104.GB1229@gaia/

I think I first heard the idea at Mark R ;).

It still needs glibc changes to avoid the mprotect(), or at least ignore
the error. Since this is an ABI change and we don't know which kernels
would have it backported, maybe better to still issue the mprotect() but
ignore the failure.

-- 
Catalin