x86: Move GDT to a safe location in RAM
Currently, the GDT is either located in FLASH or in the non-relocated U-Boot image in RAM. Both of these locations are unsafe as those locations can be erased during a U-Boot update. Move the GDT into the highest available memory location and relocate U-Boot to just below it Signed-off-by: Graeme Russ <graeme.russ@gmail.com>
This commit is contained in:
Graeme Russ
Wolfgang Denk
parent
077e1958ca
commit
c14a3669b2
|
|
@ -100,6 +100,53 @@ mem_init_ret:
|
|||
jmp get_mem_size
|
||||
get_mem_size_ret:
|
||||
|
||||
/*
|
||||
* We are now in 'Flat Protected Mode' and we know how much memory
|
||||
* the board has. The (temporary) Global Descriptor Table is not
|
||||
* in a 'Safe' place (it is either in Flash which can be erased or
|
||||
* reprogrammed or in a fail-safe boot-strap image which could be
|
||||
* over-written).
|
||||
*
|
||||
* Move the final gdt to a safe place (top of RAM) and load it.
|
||||
* This is not a trivial excercise - the lgdt instruction does not
|
||||
* have a register operand (memory only) and we may well be
|
||||
* running from Flash, so self modifying code will not work here.
|
||||
* To overcome this, we copy a stub into upper memory along with
|
||||
* the GDT.
|
||||
*/
|
||||
|
||||
/* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */
|
||||
subl $(end_gdt_setup - start_gdt_setup), %eax
|
||||
|
||||
/* Copy the GDT and Stub */
|
||||
movl $start_gdt_setup, %esi
|
||||
movl %eax, %edi
|
||||
movl $(end_gdt_setup - start_gdt_setup), %ecx
|
||||
shrl $2, %ecx
|
||||
cld
|
||||
rep movsl
|
||||
|
||||
/* write the lgdt 'parameter' */
|
||||
subl $(jmp_instr - start_gdt_setup - 4), %ebp
|
||||
addl %eax, %ebp
|
||||
movl $(gdt_ptr - start_gdt_setup), %ebx
|
||||
addl %eax, %ebx
|
||||
movl %ebx, (%ebp)
|
||||
|
||||
/* write the gdt address into the pointer */
|
||||
movl $(gdt_addr - start_gdt_setup), %ebp
|
||||
addl %eax, %ebp
|
||||
movl $(gdt - start_gdt_setup), %ebx
|
||||
addl %eax, %ebx
|
||||
movl %ebx, (%ebp)
|
||||
|
||||
/* Save the return address */
|
||||
movl $load_gdt_ret, %ebp
|
||||
|
||||
/* Load the new (safe) Global Descriptor Table */
|
||||
jmp *%eax
|
||||
|
||||
load_gdt_ret:
|
||||
/* Check we have enough memory for stack */
|
||||
movl $CONFIG_SYS_STACK_SIZE, %ecx
|
||||
cmpl %ecx, %eax
|
||||
|
|
@ -174,3 +221,52 @@ die: hlt
|
|||
blank_idt_ptr:
|
||||
.word 0 /* limit */
|
||||
.long 0 /* base */
|
||||
|
||||
.align 4
|
||||
start_gdt_setup:
|
||||
lgdt gdt_ptr
|
||||
jmp_instr:
|
||||
jmp *%ebp
|
||||
|
||||
.align 4
|
||||
gdt_ptr:
|
||||
.word 0x30 /* limit (48 bytes = 6 GDT entries) */
|
||||
gdt_addr:
|
||||
.long gdt /* base */
|
||||
|
||||
/* The GDT table ...
|
||||
*
|
||||
* Selector Type
|
||||
* 0x00 NULL
|
||||
* 0x08 Unused
|
||||
* 0x10 32bit code
|
||||
* 0x18 32bit data/stack
|
||||
* 0x20 16bit code
|
||||
* 0x28 16bit data/stack
|
||||
*/
|
||||
|
||||
.align 4
|
||||
gdt:
|
||||
.word 0, 0, 0, 0 /* NULL */
|
||||
.word 0, 0, 0, 0 /* unused */
|
||||
|
||||
.word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
|
||||
.word 0 /* base address = 0 */
|
||||
.word 0x9B00 /* code read/exec */
|
||||
.word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
|
||||
|
||||
.word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */
|
||||
.word 0x0 /* base address = 0 */
|
||||
.word 0x9300 /* data read/write */
|
||||
.word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
|
||||
|
||||
.word 0xFFFF /* 64kb */
|
||||
.word 0 /* base address = 0 */
|
||||
.word 0x9b00 /* data read/write */
|
||||
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
|
||||
|
||||
.word 0xFFFF /* 64kb */
|
||||
.word 0 /* base address = 0 */
|
||||
.word 0x9300 /* data read/write */
|
||||
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
|
||||
end_gdt_setup:
|
||||
|
|
|
|||
|
|
@ -44,7 +44,7 @@ board_init16_ret:
|
|||
movl %eax, %cr0
|
||||
wbinvd
|
||||
|
||||
/* load the descriptor tables */
|
||||
/* load the temporary Global Descriptor Table */
|
||||
o32 cs lgdt gdt_ptr
|
||||
|
||||
/* Now, we enter protected mode */
|
||||
|
|
@ -68,8 +68,13 @@ code32start:
|
|||
.long _start /* offset */
|
||||
.word 0x10 /* segment */
|
||||
|
||||
/*
|
||||
* The following Global Descriptor Table is just enough to get us into
|
||||
* 'Flat Protected Mode' - It will be discarded as soon as the final
|
||||
* GDT is setup in a safe location in RAM
|
||||
*/
|
||||
gdt_ptr:
|
||||
.word 0x30 /* limit (48 bytes = 6 GDT entries) */
|
||||
.word 0x20 /* limit (32 bytes = 4 GDT entries) */
|
||||
.long BOOT_SEG + gdt /* base */
|
||||
|
||||
/* The GDT table ...
|
||||
|
|
@ -79,8 +84,6 @@ gdt_ptr:
|
|||
* 0x08 Unused
|
||||
* 0x10 32bit code
|
||||
* 0x18 32bit data/stack
|
||||
* 0x20 16bit code
|
||||
* 0x28 16bit data/stack
|
||||
*/
|
||||
|
||||
gdt:
|
||||
|
|
@ -96,13 +99,3 @@ gdt:
|
|||
.word 0x0 /* base address = 0 */
|
||||
.word 0x9300 /* data read/write */
|
||||
.word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */
|
||||
|
||||
.word 0xFFFF /* 64kb */
|
||||
.word 0 /* base address = 0 */
|
||||
.word 0x9b00 /* data read/write */
|
||||
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
|
||||
|
||||
.word 0xFFFF /* 64kb */
|
||||
.word 0 /* base address = 0 */
|
||||
.word 0x9300 /* data read/write */
|
||||
.word 0x0010 /* granularity = 1 (+5th nibble of limit) */
|
||||
|
|
|
|||
Loading…
Reference in New Issue