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>

2 files changed, 13 insertions, 14 deletions

diff --git a/util/cbfstool/linux_trampoline.S b/util/cbfstool/linux_trampoline.S
index 65819e948b..3b4e730b33 100644
--- a/util/cbfstool/linux_trampoline.S
+++ b/util/cbfstool/linux_trampoline.S
@@ -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:
diff --git a/util/cbfstool/linux_trampoline.c b/util/cbfstool/linux_trampoline.c
index c3df214f69..87f174ceb3 100644
--- a/util/cbfstool/linux_trampoline.c
+++ b/util/cbfstool/linux_trampoline.c
@@ -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;