From: "H. Peter Anvin" <hpa@zytor.com>
To: Matthew Garrett <mjg@redhat.com>
Cc: T Makphaibulchoke <tmac@hp.com>,
tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
akpm@linux-foundation.org, yinghai@kernel.org, tiwai@suse.de,
viro@zeniv.linux.org.uk, aarcange@redhat.com,
tony.luck@intel.com, mgorman@suse.de, weiyang@linux.vnet.ibm.com,
octavian.purdila@intel.com, paul.gortmaker@windriver.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
Date: Tue, 02 Oct 2012 22:27:10 -0700 [thread overview]
Message-ID: <506BCCAE.5030203@zytor.com> (raw)
In-Reply-To: <20121003051522.GA27113@srcf.ucam.org>
On 10/02/2012 10:15 PM, Matthew Garrett wrote:
> On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote:
>
>> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem
>> *does*. The above is an exception (which is really obsolete, too: we
>> should simply disallow access to anything which is treated as system
>> RAM, which doesn't include the BIOS regions in question; the only reason
>> we don't is that some versions of X take a checksum of the RAM in the
>> first megabyte as some kind of idiotic random seed.)
>
> Oh, right, got you. In that case I think we potentially need a
> finer-grained check on EFI platforms - the EFI memory map is kind enough
> to tell us the difference between unusable regions and io regions, and
> we could avoid access to the unusable ones.
>
Well, we have the same in BIOS space with "reserved" regions. The
problem is that they are actually I/O regions as far as programs like X,
dmidecode and so on.
-hpa
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WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: Matthew Garrett <mjg@redhat.com>
Cc: T Makphaibulchoke <tmac@hp.com>,
tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
akpm@linux-foundation.org, yinghai@kernel.org, tiwai@suse.de,
viro@zeniv.linux.org.uk, aarcange@redhat.com,
tony.luck@intel.com, mgorman@suse.de, weiyang@linux.vnet.ibm.com,
octavian.purdila@intel.com, paul.gortmaker@windriver.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
Date: Tue, 02 Oct 2012 22:27:10 -0700 [thread overview]
Message-ID: <506BCCAE.5030203@zytor.com> (raw)
In-Reply-To: <20121003051522.GA27113@srcf.ucam.org>
On 10/02/2012 10:15 PM, Matthew Garrett wrote:
> On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote:
>
>> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem
>> *does*. The above is an exception (which is really obsolete, too: we
>> should simply disallow access to anything which is treated as system
>> RAM, which doesn't include the BIOS regions in question; the only reason
>> we don't is that some versions of X take a checksum of the RAM in the
>> first megabyte as some kind of idiotic random seed.)
>
> Oh, right, got you. In that case I think we potentially need a
> finer-grained check on EFI platforms - the EFI memory map is kind enough
> to tell us the difference between unusable regions and io regions, and
> we could avoid access to the unusable ones.
>
Well, we have the same in BIOS space with "reserved" regions. The
problem is that they are actually I/O regions as far as programs like X,
dmidecode and so on.
-hpa
next prev parent reply other threads:[~2012-10-03 5:27 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-02 21:32 [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine T Makphaibulchoke
2012-10-02 21:32 ` T Makphaibulchoke
2012-10-02 21:50 ` H. Peter Anvin
2012-10-02 21:50 ` H. Peter Anvin
2012-10-03 4:31 ` Matthew Garrett
2012-10-03 4:31 ` Matthew Garrett
2012-10-03 4:44 ` H. Peter Anvin
2012-10-03 4:44 ` H. Peter Anvin
2012-10-03 5:15 ` Matthew Garrett
2012-10-03 5:15 ` Matthew Garrett
2012-10-03 5:13 ` Thavatchai Makphaibulchoke
2012-10-03 5:13 ` Thavatchai Makphaibulchoke
2012-10-03 5:28 ` Matthew Garrett
2012-10-03 5:28 ` Matthew Garrett
2012-10-03 5:35 ` H. Peter Anvin
2012-10-03 5:35 ` H. Peter Anvin
2012-10-03 5:27 ` H. Peter Anvin [this message]
2012-10-03 5:27 ` H. Peter Anvin
[not found] <jQim6-6MC-7@gated-at.bofh.it>
[not found] ` <jQiFt-6UB-13@gated-at.bofh.it>
[not found] ` <jQoUx-33k-3@gated-at.bofh.it>
[not found] ` <jQp4d-37r-3@gated-at.bofh.it>
[not found] ` <jQpxf-3Cv-1@gated-at.bofh.it>
2012-10-04 20:07 ` Randy Wright
2012-10-04 21:06 ` H. Peter Anvin
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