linux-kernel - Re: [PATCH] Kconfig: Make STRICT_DEVMEM default-y on x86 and arm64

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Message-ID: <CAGXu5j+Nj-u3GXDTAoCR0wymMWzOKy3KvRLUybY4ApctCQiL9Q@mail.gmail.com>
Date:   Mon, 4 Dec 2017 10:19:26 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH] Kconfig: Make STRICT_DEVMEM default-y on x86 and arm64

On Mon, Dec 4, 2017 at 7:56 AM, Will Deacon <will.deacon@....com> wrote:
> On Fri, Dec 01, 2017 at 12:10:00PM -0800, Kees Cook wrote:
>> Distros have been shipping with CONFIG_STRICT_DEVMEM=y for years now. It
>> is probably time to flip this default for x86 and arm64.
>
> Should we be defaulting IO_STRICT_DEVMEM on as well?

I'd love to see that, but I haven't seen a long history on this
setting yet. It may be that arm64 can do it, since it doesn't have the
x86 hardware legacy stuff ... If you're willing to give it a shot, I'm
all for it. :)

-Kees

>
> Will
>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  lib/Kconfig.debug | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> index 947d3e2ed5c2..39b123d04a36 100644
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -1985,7 +1985,7 @@ config STRICT_DEVMEM
>>       bool "Filter access to /dev/mem"
>>       depends on MMU && DEVMEM
>>       depends on ARCH_HAS_DEVMEM_IS_ALLOWED
>> -     default y if TILE || PPC
>> +     default y if TILE || PPC || X86 || ARM64
>>       ---help---
>>         If this option is disabled, you allow userspace (root) access to all
>>         of memory, including kernel and userspace memory. Accidental
>> --
>> 2.7.4
>>
>>
>> --
>> Kees Cook
>> Pixel Security



-- 
Kees Cook
Pixel Security