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linux_trampoline: use trampoline RAM for the GDT 

The linux trampoline was modifying the existing GDT
to add the 0x10 and 0x18 descriptors for Linux.
This will not work when the existing GDT is in ROM.

Change the code to set up a new GDT in what we know to be
RAM.

Tested by booting a linux payload. The main reason this works
is that Linux almost immediately loads its own GDT and then
segment registers. This GDT is a very temporary bridge.

Note that none of this change used to be necessary; the coreboot
GDT was originally compatible with Linux (ca 2000);
then Linux changed.

Change-Id: I13990052fbfd6a500adab8a2db8f7aead1d24fa6
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/27529
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
This commit is contained in:
Ronald G. Minnich 2018-07-18 07:19:30 -07:00
parent ebde659503
commit eeb83b6b53
2 changed files with 13 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
util/cbfstool/linux_trampoline.S
View File

@ -31,7 +31,6 @@
#define E820_OFFSET 0x2d0
.trampoline_start:
cld
xor %edx, %edx
mov $0, %ecx
@ -114,12 +113,13 @@ jnz .tableScan
** Use TRAMPOLINE_ENTRY_LOC as a scratchpad.
*/
mov $TRAMPOLINE_ENTRY_LOC, %eax
sgdt (%eax)
mov 2(%eax), %ebx
movl $0x0000ffff, 16(%ebx)
movl $0x00cf9b00, 20(%ebx)
movl $0x0000ffff, 24(%ebx)
movl $0x00cf9300, 28(%ebx)
movl $0x0000ffff, 16(%eax) // Set up the 2 new descriptors
movl $0x00cf9b00, 20(%eax)
movl $0x0000ffff, 24(%eax)
movl $0x00cf9300, 28(%eax)
movb $0x2b, 0(%eax) // Set the size
movl %eax, 2(%eax) // Set pointer to new GDT
lgdt (%eax) // Load it
/* finally: jump to kernel */
mov $LINUX_PARAM_LOC, %esi
@ -129,5 +129,4 @@ jmp *(LINUX_PARAM_LOC + LINUX_ENTRY_OFFSET)
2:
hlt
jmp 2b
.trampoline_end:

12
util/cbfstool/linux_trampoline.c
View File

@ -2,15 +2,15 @@
unsigned char trampoline[] = {
0xfc, 0x31, 0xd2, 0xb9, 0x00, 0x00, 0x00, 0x00, 0xbb, 0x00, 0x00, 0x01, 0x00, 0x01, 0xcb, 0x8b,
0x01, 0x3d, 0x4c, 0x42, 0x49, 0x4f, 0x74, 0x07, 0x83, 0xc1, 0x10, 0x39, 0xcb, 0x75, 0xe9, 0x39,
0xcb, 0x0f, 0x84, 0x87, 0x00, 0x00, 0x00, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83,
0xcb, 0x0f, 0x84, 0x8a, 0x00, 0x00, 0x00, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83,
0x3b, 0x11, 0x75, 0x05, 0x8b, 0x4b, 0x08, 0xeb, 0xcf, 0x83, 0x3b, 0x01, 0x75, 0x33, 0x8b, 0x43,
0x04, 0x83, 0xe8, 0x08, 0xc1, 0xe8, 0x02, 0x3d, 0xa0, 0x00, 0x00, 0x00, 0x7e, 0x05, 0xb8, 0xa0,
0x00, 0x00, 0x00, 0x89, 0xc6, 0xbf, 0x05, 0x00, 0x00, 0x00, 0xf7, 0xf7, 0xa3, 0xe8, 0x01, 0x09,
0x00, 0x89, 0xf0, 0x91, 0x8d, 0x73, 0x08, 0xbf, 0xd0, 0x02, 0x09, 0x00, 0xf3, 0xa5, 0x91, 0xeb,
0x05, 0x83, 0x3b, 0x12, 0x75, 0x00, 0x03, 0x5b, 0x04, 0x49, 0x75, 0xb3, 0xb8, 0x00, 0x00, 0x04,
0x00, 0x0f, 0x01, 0x00, 0x8b, 0x58, 0x02, 0xc7, 0x43, 0x10, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x43,
0x14, 0x00, 0x9b, 0xcf, 0x00, 0xc7, 0x43, 0x18, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x43, 0x1c, 0x00,
0x93, 0xcf, 0x00, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14, 0x02, 0x09, 0x00, 0xf4, 0xeb,
0xfd
0x00, 0xc7, 0x40, 0x10, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x40, 0x14, 0x00, 0x9b, 0xcf, 0x00, 0xc7,
0x40, 0x18, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x40, 0x1c, 0x00, 0x93, 0xcf, 0x00, 0xc6, 0x00, 0x2b,
0x89, 0x40, 0x02, 0x0f, 0x01, 0x10, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14, 0x02, 0x09,
0x00, 0xf4, 0xeb, 0xfd
};
unsigned int trampoline_len = 177;
unsigned int trampoline_len = 180;