[coreboot-gerrit] New patch to review for coreboot: 960e7f5 cbfstool:linux_trampoline: config CS and DS segment descriptors
Curt Brune (curt@cumulusnetworks.com)
gerrit at coreboot.org
Fri Aug 29 19:48:14 CEST 2014
Curt Brune (curt at cumulusnetworks.com) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/6796
-gerrit
commit 960e7f56b1abd277fa1173a9d1c986e882d52537
Author: Curt Brune <curt at cumulusnetworks.com>
Date: Fri Aug 29 10:43:36 2014 -0700
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.
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 at cumulusnetworks.com>
---
util/cbfstool/linux_trampoline.c | 38 +++++++++++++++++++++++++++++++-------
1 file changed, 31 insertions(+), 7 deletions(-)
diff --git a/util/cbfstool/linux_trampoline.c b/util/cbfstool/linux_trampoline.c
index 368d63a..1a1dccf 100644
--- a/util/cbfstool/linux_trampoline.c
+++ b/util/cbfstool/linux_trampoline.c
@@ -101,6 +101,28 @@ 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
+*/
+mov %esp, %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 +150,15 @@ 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, 0x89, 0xe0, 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;
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