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 01:17:23 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Sasha Levin <sashal@...nel.org>
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 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

-- 
 Kirill A. Shutemov