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

From: Sasha Levin
Date: Fri Aug 30 2019 - 08:06:42 EST

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@xxxxxxxxxxxxx>

[ 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

Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

Please postpone backporting the patch (and into other trees). There's a
fixup for it:


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?