[bug #55849] GRUB2 wrongly uses EBDA

[Chu-Hsuan]

URL:
  <https://savannah.gnu.org/bugs/?55849>

                 Summary: GRUB2 wrongly uses EBDA
                 Project: GNU GRUB
            Submitted by: chuhsuan
            Submitted on: Thu 07 Mar 2019 09:48:22 AM UTC
                Category: Booting
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: 2.02
         Reproducibility: Every Time
         Planned Release: None

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Details:

In grub_acpi_create_ebda() in grub-core/commands/acpi.c, it wrongly use EBDA
with hard code.

1. It should not copy only first 0x400 bytes to new EBDA. The total size
should be copied to new EBDA is based on original size. If original EBDA size
is 0x2 (the first word of EBDA), it means it should copy 2*0x400 bytes to new
EBDA.

2. It should not hard code to add "1" to new EBDA size. It should calculate
based on how much size it created. For example, original EBDA is 9f80:0 and
size is 0x2 (unit is 1K) and new EBDA is 9e80:0. Because 9f80:0 - 9e80:0 is
4K, the new EBDA size should be 0x2+0x4 = 0x6.

3. Keep original data at the same offset and use higher memory partion. For
example, original EBDA is 9f80:0 and size is 0x2 and new EBDA is 9e80:0. In
this case, it should copy data from 9f80:0 ~ 9fff:f to 9e80:0 ~ 9eff:f and new
9f00:0 to 9fff:f is available for GRUB2.

I know there is a "--no-ebda" option, but it should not wrongly use EBDA since
it decide to use it.





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