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Bug 655381 - Wrong VESA VBE BIOS support in GRUB
Summary: Wrong VESA VBE BIOS support in GRUB
Alias: None
Product: Fedora
Classification: Fedora
Component: grub
Version: 14
Hardware: i686
OS: Linux
Target Milestone: ---
Assignee: Peter Jones
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2010-11-20 18:47 UTC by Martin Decky
Modified: 2012-08-16 19:49 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2012-08-16 19:49:06 UTC
Type: ---

Attachments (Terms of Use)
Patch changing the size of "struct vbe_mode" to 256 bytes (409 bytes, patch)
2010-11-20 18:48 UTC, Martin Decky
no flags Details | Diff

Description Martin Decky 2010-11-20 18:47:04 UTC
Description of problem:

GRUB has two builtin commands "vbeprobe" and "testvbe" which are intended to test VESA VBE BIOS graphics modes (e.g. for manually testing the correct Linux VESA framebuffer mode before setting the vga= kernel command line value).

However, on many recent graphics cards which are VESA 3.0 compliant these commands do not work. The reason is a wrong definition of the vbe_mode structure in stage2/shared.h. The VBE mode info structure should be 256 bytes long, but here it is actually only 255 bytes long, the array "unsigned char reserved3[189]" should be actually declared as "unsigned char reserved3[190]" (frankly, the same mistake is also present in the official VESA VBE 3.0 specification document).

As the vbe_mode structure is allocated on stack in vbeprobe_func() and testvbe_func() (stage2/builtins.c), if the VESA BIOS actually stores all 256 bytes in the 0x4f01 call (Get Mode Info), the last byte overruns the structure and ends in a different variable on the stack (mode_number in case of vbeprobe_func()), thus rendering both routines unfunctional.

Version-Release number of selected component (if applicable):

grub-0.97-68.fc14.x86_64 (affects probably all releases of GRUB Legacy)

How reproducible:

Always on many recent graphics cards with VGA BIOS compliant to VESA VBE 3.0 which actually store 256 bytes in the 0x4f01 call.

Steps to Reproduce:

1. While in GRUB (during boot time) go to the command line.
2. Try using the "vbeprobe" or "testvbe" commands.
Actual results:

No list of supported VESA modes is printed and no VESA mode can be tested (even those which are definitively supported by the hardware).

Expected results:

The "vbeprobe" should print out a list of supported VESA modes and "testvbe" should be able to test them.

Comment 1 Martin Decky 2010-11-20 18:48:38 UTC
Created attachment 461753 [details]
Patch changing the size of "struct vbe_mode" to 256 bytes

Comment 2 Fedora End Of Life 2012-08-16 19:49:08 UTC
This message is a notice that Fedora 14 is now at end of life. Fedora 
has stopped maintaining and issuing updates for Fedora 14. It is 
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