linux-kernel - Re: [PATCH AUTOSEL 5.2 51/76] x86/boot/compressed/64: Fix boot on machines with broken E820 table

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Date:   Fri, 30 Aug 2019 08:06:38 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>
Subject: Re: [PATCH AUTOSEL 5.2 51/76] x86/boot/compressed/64: Fix boot on
 machines with broken E820 table

On Fri, Aug 30, 2019 at 01:17:23AM +0300, Kirill A. Shutemov wrote:
>On Thu, Aug 29, 2019 at 02:12:46PM -0400, Sasha Levin wrote:
>> From: "Kirill A. Shutemov" <kirill@...temov.name>
>>
>> [ Upstream commit 0a46fff2f9108c2c44218380a43a736cf4612541 ]
>>
>> BIOS on Samsung 500C Chromebook reports very rudimentary E820 table that
>> consists of 2 entries:
>>
>>   BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] usable
>>   BIOS-e820: [mem 0x00000000fffff000-0x00000000ffffffff] reserved
>>
>> It breaks logic in find_trampoline_placement(): bios_start lands on the
>> end of the first 4k page and trampoline start gets placed below 0.
>>
>> Detect underflow and don't touch bios_start for such cases. It makes
>> kernel ignore E820 table on machines that doesn't have two usable pages
>> below BIOS_START_MAX.
>>
>> Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Signed-off-by: Borislav Petkov <bp@...e.de>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: x86-ml <x86@...nel.org>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203463
>> Link: https://lkml.kernel.org/r/20190813131654.24378-1-kirill.shutemov@linux.intel.com
>> Signed-off-by: Sasha Levin <sashal@...nel.org>
>
>Please postpone backporting the patch (and into other trees). There's a
>fixup for it:
>
>http://lore.kernel.org/r/20190826133326.7cxb4vbmiawffv2r@box

Sure. Should I just queue it up for a week or two later (along with the
fixes), or do you want to let me know when?

--
Thanks,
Sasha