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From:   Florian Weimer <fweimer@redhat.com>
To:     Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc:     libc-alpha@sourceware.org, Jeremy Linton <jeremy.linton@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Salvatore Mesoraca <s.mesoraca16@gmail.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        Topi Miettinen <toiwoton@gmail.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel-hardening@lists.openwall.com,
        linux-hardening@vger.kernel.org
Subject: Re: [PATCH 3/4] aarch64: Use mmap to add PROT_BTI instead of
 mprotect [BZ #26831]
References: <cover.1604393169.git.szabolcs.nagy@arm.com>
        <f5eaa74cb7538382b2fd2439755386ac68f7c8db.1604393169.git.szabolcs.nagy@arm.com>
Date:   Tue, 03 Nov 2020 11:34:22 +0100
In-Reply-To: <f5eaa74cb7538382b2fd2439755386ac68f7c8db.1604393169.git.szabolcs.nagy@arm.com>
        (Szabolcs Nagy's message of "Tue, 3 Nov 2020 10:26:29 +0000")
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* Szabolcs Nagy:

> Re-mmap executable segments if possible instead of using mprotect
> to add PROT_BTI. This allows using BTI protection with security
> policies that prevent mprotect with PROT_EXEC.
>
> If the fd of the ELF module is not available because it was kernel
> mapped then mprotect is used and failures are ignored.  It is
> expected that linux kernel will add PROT_BTI when mapping a module
> (current linux as of version 5.9 does not do this).
>
> Computing the mapping parameters follows the logic of
> _dl_map_object_from_fd more closely now.

What's the performance of this on execve-heavy workloads, such as kernel
or glibc builds?  Hopefully it's cheap because these mappings have not
been faulted in yet.

Thanks,
Florian
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