New patch to review for coreboot: 960e7f5 cbfstool:linux_trampoline: config CS and DS segment descriptors
Curt Brune (curt@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@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@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;
-
Curt Brune