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Subject: Re: x86/mm: Found insecure W+X mapping at address (ptrval)/0xc00a0000
To:     Borislav Petkov <bp@alien8.de>,
        =?UTF-8?B?SsO2cmcgUsO2ZGVs?= <joro@8bytes.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-mm@kvack.org,
        x86@kernel.org, lkml <linux-kernel@vger.kernel.org>
References: <e75fa739-4bcc-dc30-2606-25d2539d2653@molgen.mpg.de>
 <alpine.DEB.2.21.1809191004580.1468@nanos.tec.linutronix.de>
 <0922cc1b-ed51-06e9-df81-57fd5aa8e7de@molgen.mpg.de>
 <alpine.DEB.2.21.1809210045220.1434@nanos.tec.linutronix.de>
 <c8da5778-3957-2fab-69ea-42f872a5e396@molgen.mpg.de>
 <alpine.DEB.2.21.1809281653270.2004@nanos.tec.linutronix.de>
 <20181003212255.GB28361@zn.tnic> <20181004080321.GA3630@8bytes.org>
 <20181004081429.GB1864@zn.tnic>
From:   Paul Menzel <pmenzel@molgen.mpg.de>
Message-ID: <6cbb9135-7e89-748f-1d55-ac105a9f8091@molgen.mpg.de>
Date:   Thu, 4 Oct 2018 10:40:49 +0200
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Dear Borislav,


On 10/04/18 10:14, Borislav Petkov wrote:
> On Thu, Oct 04, 2018 at 10:03:21AM +0200, Joerg Roedel wrote:
>> I also triggered this when working in the PTI-x32 code. It always
>> happens on a 32-bit PAE kernel for me.
>>
>> Tracking it down I ended up in (iirc) arch/x86/mm/pageattr.c
>> 	function static_protections():
>>
>> 		/*
>> 		 * The BIOS area between 640k and 1Mb needs to be executable for
>> 		 * PCI BIOS based config access (CONFIG_PCI_GOBIOS) support.
>> 		 */
>> 	#ifdef CONFIG_PCI_BIOS
>> 		if (pcibios_enabled && within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_EN=
D >> PAGE_SHIFT))
>> 			pgprot_val(forbidden) |=3D _PAGE_NX;
>> 	#endif
>>
>> I think that is the reason we are seeing this in that configuration.
>=20
> So looking at this, BIOS_BEGIN and BIOS_END is the same range as the IS=
A
> range:
>=20
> #define ISA_START_ADDRESS       0x000a0000
> #define ISA_END_ADDRESS         0x00100000
>=20
> #define BIOS_BEGIN              0x000a0000
> #define BIOS_END                0x00100000
>=20
> and I did try marking the ISA range RO in mark_rodata_ro() but the=20
> machine wouldn't boot after. So I'm guessing BIOS needs to write
> there some crap.

Do you have a commit, I could test. My board is supported by coreboot,
and maybe it boots, so I can check, if the warning is gone.


Kind regards,

Paul


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