cbfstool:linux_trampoline: config CS and DS segment descriptors

The Linux trampoline code does not set up the segment descriptors for
__BOOT_CS and __BOOT_DS as described in the Linux kernel
documentation:

  ... a GDT must be loaded with the descriptors for selectors
  __BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G
  flat segment; __BOOT_CS must have execute/read permission, and
  __BOOT_DS must have read/write permission;

This is not a problem when launching a Linux payload from coreboot, as
coreboot configures the segment descriptors at selectors 0x10 and
0x18.  Coreboot configures these selectors in the ramstage to match
what the Linux kernel expects (see
coreboot/src/arch/x86/lib/c_start.S).

When the cbfs payload is launched in other environments, SeaBIOS for
example, the segment descriptors are configured differently and the
cbfs Linux payload does not work.

If the cbfs Linux payload is to be used in multiple environments
should the trampoline needs to take care of the descriptors that Linux
requires.

This patch updates the Linux trampoline code to configure the 4G flat
descriptors that Linux expects.  The configuration is borrowed from
the descriptor configs in coreboot/src/arch/x86/lib/c_start.S for
selectors 0x10 and 0x18.

The linux_trampoline code is slightly refractored by defining the
trampoline entry address, 0x40000, as TRAMPOLINE_ENTRY_LOC.  This
definition is moved into a separate header file, linux_trampoline.h.
This header file is now included by both the trampoline assembly
language code and the trampoline loader C code.

The trampoline assembly language code can now use TRAMPOLINE_ENTRY_LOC
as scratch space for the sgdt CPU instruction.

Testing Done:

Verified the Linux payload is booted correctly in the following
environments:

1.  Coreboot -> Linux Payload

2.  Coreboot -> SeaBIOS -> Linux Payload: (previously did not work)

Change-Id: I888f74ff43073a6b7318f6713a8d4ecb804c0162
Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
Reviewed-on: http://review.coreboot.org/6796
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

4 files changed, 79 insertions, 16 deletions

diff --git a/util/cbfstool/cbfs-payload-linux.c b/util/cbfstool/cbfs-payload-linux.c
index 33a5e1a..9e9a874 100644
--- a/util/cbfstool/cbfs-payload-linux.c
+++ b/util/cbfstool/cbfs-payload-linux.c
@@ -302,9 +302,8 @@ int parse_bzImage_to_payload(const struct buffer *input,
 	                   PAYLOAD_SEGMENT_CODE, kernel_base);
 
 	/* trampoline */
-	uint64_t entrypoint = 0x40000; /*TODO: any better place? */
 	bzp_output_segment(&bzp, &bzp.trampoline,
-	                   PAYLOAD_SEGMENT_CODE, entrypoint);
+	                   PAYLOAD_SEGMENT_CODE, TRAMPOLINE_ENTRY_LOC);
 
 	/* cmdline */
 	bzp_output_segment(&bzp, &bzp.cmdline,
@@ -315,7 +314,7 @@ int parse_bzImage_to_payload(const struct buffer *input,
 	                   PAYLOAD_SEGMENT_DATA, initrd_base);
 
 	/* Terminating entry segment. */
-	bzp_output_segment(&bzp, NULL, PAYLOAD_SEGMENT_ENTRY, entrypoint);
+	bzp_output_segment(&bzp, NULL, PAYLOAD_SEGMENT_ENTRY, TRAMPOLINE_ENTRY_LOC);
 
 	/* Set size of buffer taking into account potential compression. */
 	buffer_set_size(&bzp.output, bzp.offset);
diff --git a/util/cbfstool/linux.h b/util/cbfstool/linux.h
index 20837e3..ae747e6 100644
--- a/util/cbfstool/linux.h
+++ b/util/cbfstool/linux.h
@@ -26,17 +26,13 @@
  */
 
 #include <stdint.h>
+#include "linux_trampoline.h"
 
 typedef uint8_t u8;
 typedef uint16_t u16;
 typedef uint32_t u32;
 typedef uint64_t u64;
 
-#define LINUX_PARAM_LOC 0x90000
-#define COMMAND_LINE_LOC 0x91000
-#define GDT_LOC 0x92000
-#define STACK_LOC 0x93000
-
 #define E820MAX	32		/* number of entries in E820MAP */
 struct e820entry {
 	unsigned long long addr;	/* start of memory segment */
diff --git a/util/cbfstool/linux_trampoline.c b/util/cbfstool/linux_trampoline.c
index 368d63a..649bb64 100644
--- a/util/cbfstool/linux_trampoline.c
+++ b/util/cbfstool/linux_trampoline.c
@@ -24,12 +24,13 @@
  */
 .code32
 .data
+
+#include "linux_trampoline.h"
 #define HEADER_SIG 0x4f49424c // LBIO little endian
 #define CB_TAG_FORWARD 0x11
 #define CB_TAG_MEMORY 0x1
 #define CB_TAG_FRAMEBUFFER 0x12
 
-#define LINUX_PARAM_LOC 0x90000
 #define E820_NR_OFFSET 0x1e8
 #define LINUX_ENTRY_OFFSET 0x214
 #define E820_OFFSET 0x2d0
@@ -101,6 +102,30 @@ add 4(%ebx), %ebx
 dec %ecx
 jnz .tableScan
 
+/* Setup basic code and data segment selectors for Linux
+**
+** Flat code segment descriptor:
+**   selector: 0x10
+**   base    : 0x00000000
+**   limit   : 0xFFFFFFFF
+**   type    : code, execute, read
+**
+** Flat data segment descriptor:
+**   selector: 0x18
+**   base    : 0x00000000
+**   limit   : 0xFFFFFFFF
+**   type    : data, read/write
+**
+** 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)
+
 /* finally: jump to kernel */
 mov $LINUX_PARAM_LOC, %esi
 jmp *(LINUX_PARAM_LOC + LINUX_ENTRY_OFFSET)
@@ -128,13 +153,16 @@ trampoline_size:
 const 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, 0x74, 0x60, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83, 0x3b, 0x11, 0x75, 0x05,
-0x8b, 0x4b, 0x08, 0xeb, 0xd3, 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, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14,
-0x02, 0x09, 0x00, 0xf4, 0xeb, 0xfd
+0xcb, 0x0f, 0x84, 0x85, 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
 };
 
 const void * const trampoline_start = &trampoline;
diff --git a/util/cbfstool/linux_trampoline.h b/util/cbfstool/linux_trampoline.h
new file mode 100644
index 0000000..ed5b824
--- /dev/null
+++ b/util/cbfstool/linux_trampoline.h
@@ -0,0 +1,40 @@
+/*
+ * This file is part of coreboot..
+ *
+ * Based on work by Patrick Georgi <patrick@georgi-clan.de>
+ * Copyright 2014 Curt Brune <curt@cumulusnetworks.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+/*
+ * This file contains #define constants used by both the Linux
+ * trampoline C-code and assembly language code.  As such it can only
+ * contain preprocessor macros.  Do not inlucde C language
+ * declarations in this file.
+ */
+
+#ifndef LINUX_TRAMPOLINE_H__
+#define LINUX_TRAMPOLINE_H__
+
+/*
+ * Trampoline entry point
+ * TODO: any better place?
+ */
+#define TRAMPOLINE_ENTRY_LOC 0x40000
+
+#define LINUX_PARAM_LOC 0x90000
+#define COMMAND_LINE_LOC 0x91000
+
+#endif /* LINUX_TRAMPOLINE_H__ */