RE: [PATCH] ACPICA: Tables: Skip NULL entries in RSDT and XSDT.

[Zheng, Lv]

Hi,

> From: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx]
> Sent: Friday, April 18, 2014 10:44 AM
> 
> On Fri, Apr 18, 2014 at 09:53:19AM +0800, Lv Zheng wrote:
> > Note that this patch is only used for stable kernels, upstream kernels
> > will have this problem fixed in ACPICA 201303-04 release.  So upstream
> > kernels shouldn't merge this commit.
> 
> What kernel commit fixed this issue in "upstream"?
> 
> > It is reported that there are buggy BIOSes in the world: AMI uses a XSDt
> > compiler for early BIOSes, this compiler will generate XSDT with a NULL
> > entry.  The affected BIOS versions are "AMI BIOS F2-F4".
> >
> > Original solution on Linux is to use an alternative heathy root table
> > instead of the ill one.  This commit is refined by the following ACPICA
> > commit that tries to reduce the source code differences between Linux and
> > ACPICA upstream.
> >   Commit: 671cc68dc61f029d44b43a681356078e02d8dab8
> >   Subject: ACPICA: Back port and refine validation of the XSDT root table.
> > But according to the bug report, the XSDT in fact is not broken, we should
> > just add NULL entry sanity check before installing a table address from
> > XSDT.
> >
> > With the NULL entry sanity check implemented, the XSDT validation is
> > useless because:
> > 1. If XSDT contains NULL entries, it can be bypassed by the new sanity
> >    check mechanism;
> > 2. If RSDP contains a bad XSDT address, invoking XSDT validation will still
> >    lead to kernel crash.
> >
> > This patch deletes XSDT validation logics and adds code to skip NULL
> > entries that can be found in RSDT or XSDT. Lv Zheng.
> >
> > Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=73911
> > Buglink: https://bugs.archlinux.org/task/39811
> > Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx>
> > Reported-and-tested-by: Bruce Chiarelli <mano155@xxxxxxxxx>
> > Reported-and-tested-by: Spyros Stathopoulos <spystath@xxxxxxxxx>
> > Cc: Zhao Yakui <yakui.zhao@xxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx> # 3.14.x: 671cc68: ACPICA: Back port and refine validation of the XSDT root table.
> 
> So this fix is only needed for 3.14?  Or older?  I'm confused here...

Only 3.14.1 - 3.15.1 kernels are affected.  Others are fine.
Possibly this urgent commit is useful for the users currently running 3.14 on such broken platforms.
I haven't obtained Rafael's ACKs on this.  We may discuss it in next week.

Thanks and best regards
-Lv

> greg k-h
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