Re: [PATCH] hpet, allow user controlled mmap for user processes

From: Clemens Ladisch
Date: Tue Mar 19 2013 - 03:43:33 EST

Prarit Bhargava wrote:
> The CONFIG_HPET_MMAP Kconfig option exposes the memory map of the HPET
> registers to userspace. The Kconfig help points out that in some cases this
> can be a security risk as some systems may erroneously configure the map such
> that additional data is exposed to userspace.
> This is a problem for distributions -- some users want the MMAP functionality
> but it comes with a significant security risk. In an effort to mitigate this
> risk, and due to the low number of users of the MMAP functionality, I've
> introduced a kernel parameter, hpet_mmap_enable, that is required in order
> to actually have the HPET MMAP exposed.
> [v2]: Clemens suggested modifying the Kconfig help text and making the
> default setting configurable.
> Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
> Cc: Clemens Ladisch <clemens@xxxxxxxxxx>

> +++ b/Documentation/kernel-parameters.txt
> + hpet_mmap_enable [X86, HPET_MMAP] option to expose HPET MMAP to
> + userspace. By default this is disabled.

This now takes a value.

> + int "Enable HPET MMAP access by default"
> + range 0 1

Shouldn't this be bool?

> + default 0

This breaks backwards compatibility.

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