linux-kernel - Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

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Message-ID: <1297108754.4d504f1281802@imp.free.fr>
Date:	Mon, 07 Feb 2011 20:59:14 +0100
From:	castet.matthieu@...e.fr
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	castet.matthieu@...e.fr, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Matthias Hopf <mhopf@...e.de>, rjw@...k.pl,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

Thanks for cleaning the patch.

Selon "H. Peter Anvin" <hpa@...or.com>:
> On 02/05/2011 08:46 AM, castet.matthieu@...e.fr wrote:
>
> No, the problem is that the code is braindamaged and don't take into
> account reserved areas or have a mechanism for marking the reserved
> areas so that kernel_physical_mapping_init can do the right thing... and
> then it's hacked around instead of done properly.
>
> We obviously need to reserve this memory very early in order to make
> sure it exists, and init_memory_mapping() ->
> kernel_physical_mapping_init() really should be able to deal with that
> (for example by walking the list of reserved memory regions and look
> which ones of them should have specific protection bits -- not just NX
> -- set appropriately.)
>
> The trampoline unification patch could have made this less broken, but
> that code is certainly not ready for .38.
>
For .39 I hope we could remove most of the RWX rights after init (This means
make low memory trampoline NX or !RW).
This should be possible on :
- 32 bit if wakeup use trampoline_32 [1] that doesn't enable paging in low
memory (can be NX)
- trampoline_64 need fix to support NX on data section. It tries to read data
section before enabling NX. A possible fix is to use its own page table [2]. And
the kernel one can be NX.


Matthieu


[1]
http://marc.info/?l=linux-acpi&m=129616540303575&w=2

[2]
http://marc.info/?l=linux-kernel&m=129590778414274&w=2
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