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linux-next/arch/x86_64/kernel/head.S
Eric W. Biederman 26374c7b7d [PATCH] Reload CS when startup_64 is used. 
In long mode the %cs is largely a relic.  However there are a few cases
like iret where it matters that we have a valid value.  Without this
patch it is possible to enter the kernel in startup_64 without setting
%cs to a valid value.  With this patch we don't care what %cs value
we enter the kernel with, so long as the cs shadow register indicates
it is a privileged code segment.

Thanks to Magnus Damm for finding this problem and posting the
first workable patch.  I have moved the jump to set %cs down a
few instructions so we don't need to take an extra jump.  Which
keeps the code simpler.

Signed-of-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andi Kleen <ak@suse.de>
2006-09-26 10:52:38 +02:00

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/*
* linux/arch/x86_64/kernel/head.S -- start in 32bit and switch to 64bit
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
* Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
* Copyright (C) 2000 Karsten Keil <kkeil@suse.de>
* Copyright (C) 2001,2002 Andi Kleen <ak@suse.de>
*/
#include <linux/linkage.h>
#include <linux/threads.h>
#include <linux/init.h>
#include <asm/desc.h>
#include <asm/segment.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/cache.h>
/* we are not able to switch in one step to the final KERNEL ADRESS SPACE
* because we need identity-mapped pages on setup so define __START_KERNEL to
* 0x100000 for this stage
*
*/
.text
.section .bootstrap.text
.code32
.globl startup_32
/* %bx: 1 if coming from smp trampoline on secondary cpu */
startup_32:
/*
* At this point the CPU runs in 32bit protected mode (CS.D = 1) with
* paging disabled and the point of this file is to switch to 64bit
* long mode with a kernel mapping for kerneland to jump into the
* kernel virtual addresses.
* There is no stack until we set one up.
*/
/* Initialize the %ds segment register */
movl $__KERNEL_DS,%eax
movl %eax,%ds
/* Load new GDT with the 64bit segments using 32bit descriptor */
lgdt pGDT32 - __START_KERNEL_map
/* If the CPU doesn't support CPUID this will double fault.
* Unfortunately it is hard to check for CPUID without a stack.
*/
/* Check if extended functions are implemented */
movl $0x80000000, %eax
cpuid
cmpl $0x80000000, %eax
jbe no_long_mode
/* Check if long mode is implemented */
mov $0x80000001, %eax
cpuid
btl $29, %edx
jnc no_long_mode
/*
* Prepare for entering 64bits mode
*/
/* Enable PAE mode */
xorl %eax, %eax
btsl $5, %eax
movl %eax, %cr4
/* Setup early boot stage 4 level pagetables */
movl $(boot_level4_pgt - __START_KERNEL_map), %eax
movl %eax, %cr3
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
/* Enable Long Mode */
btsl $_EFER_LME, %eax
/* Make changes effective */
wrmsr
xorl %eax, %eax
btsl $31, %eax /* Enable paging and in turn activate Long Mode */
btsl $0, %eax /* Enable protected mode */
/* Make changes effective */
movl %eax, %cr0
/*
* At this point we're in long mode but in 32bit compatibility mode
* with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn
* EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use
* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
*/
ljmp $__KERNEL_CS, $(startup_64 - __START_KERNEL_map)
.code64
.org 0x100
.globl startup_64
startup_64:
/* We come here either from startup_32
* or directly from a 64bit bootloader.
* Since we may have come directly from a bootloader we
* reload the page tables here.
*/
/* Enable PAE mode and PGE */
xorq %rax, %rax
btsq $5, %rax
btsq $7, %rax
movq %rax, %cr4
/* Setup early boot stage 4 level pagetables. */
movq $(boot_level4_pgt - __START_KERNEL_map), %rax
movq %rax, %cr3
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
movl %edx,%edi
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
/* Enable System Call */
btsl $_EFER_SCE, %eax
/* No Execute supported? */
btl $20,%edi
jnc 1f
btsl $_EFER_NX, %eax
1:
/* Make changes effective */
wrmsr
/* Setup cr0 */
#define CR0_PM 1 /* protected mode */
#define CR0_MP (1<<1)
#define CR0_ET (1<<4)
#define CR0_NE (1<<5)
#define CR0_WP (1<<16)
#define CR0_AM (1<<18)
#define CR0_PAGING (1<<31)
movl $CR0_PM|CR0_MP|CR0_ET|CR0_NE|CR0_WP|CR0_AM|CR0_PAGING,%eax
/* Make changes effective */
movq %rax, %cr0
/* Setup a boot time stack */
movq init_rsp(%rip),%rsp
/* zero EFLAGS after setting rsp */
pushq $0
popfq
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
* addresses where we're currently running on. We have to do that here
* because in 32bit we couldn't load a 64bit linear address.
*/
lgdt cpu_gdt_descr
/*
* Setup up a dummy PDA. this is just for some early bootup code
* that does in_interrupt()
*/
movl $MSR_GS_BASE,%ecx
movq $empty_zero_page,%rax
movq %rax,%rdx
shrq $32,%rdx
wrmsr
/* set up data segments. actually 0 would do too */
movl $__KERNEL_DS,%eax
movl %eax,%ds
movl %eax,%ss
movl %eax,%es
/* esi is pointer to real mode structure with interesting info.
pass it to C */
movl %esi, %edi
/* Finally jump to run C code and to be on real kernel address
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*/
movq initial_code(%rip),%rax
pushq $0 # fake return address to stop unwinder
pushq $__KERNEL_CS # set correct cs
pushq %rax # target address in negative space
lretq
/* SMP bootup changes these two */
.align 8
.globl initial_code
initial_code:
.quad x86_64_start_kernel
.globl init_rsp
init_rsp:
.quad init_thread_union+THREAD_SIZE-8
ENTRY(early_idt_handler)
cmpl $2,early_recursion_flag(%rip)
jz 1f
incl early_recursion_flag(%rip)
xorl %eax,%eax
movq 8(%rsp),%rsi # get rip
movq (%rsp),%rdx
movq %cr2,%rcx
leaq early_idt_msg(%rip),%rdi
call early_printk
cmpl $2,early_recursion_flag(%rip)
jz 1f
call dump_stack
#ifdef CONFIG_KALLSYMS
leaq early_idt_ripmsg(%rip),%rdi
movq 8(%rsp),%rsi # get rip again
call __print_symbol
#endif
1: hlt
jmp 1b
early_recursion_flag:
.long 0
early_idt_msg:
.asciz "PANIC: early exception rip %lx error %lx cr2 %lx\n"
early_idt_ripmsg:
.asciz "RIP %s\n"
.code32
ENTRY(no_long_mode)
/* This isn't an x86-64 CPU so hang */
1:
jmp 1b
.org 0xf00
.globl pGDT32
pGDT32:
.word gdt_end-cpu_gdt_table-1
.long cpu_gdt_table-__START_KERNEL_map
.org 0xf10
ljumpvector:
.long startup_64-__START_KERNEL_map
.word __KERNEL_CS
ENTRY(stext)
ENTRY(_stext)
$page = 0
#define NEXT_PAGE(name) \
$page = $page + 1; \
.org $page * 0x1000; \
phys_/**/name = $page * 0x1000 + __PHYSICAL_START; \
ENTRY(name)
NEXT_PAGE(init_level4_pgt)
/* This gets initialized in x86_64_start_kernel */
.fill 512,8,0
NEXT_PAGE(level3_ident_pgt)
.quad phys_level2_ident_pgt | 0x007
.fill 511,8,0
NEXT_PAGE(level3_kernel_pgt)
.fill 510,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
.quad phys_level2_kernel_pgt | 0x007
.fill 1,8,0
NEXT_PAGE(level2_ident_pgt)
/* 40MB for bootup. */
i = 0
.rept 20
.quad i << 21 | 0x083
i = i + 1
.endr
/* Temporary mappings for the super early allocator in arch/x86_64/mm/init.c */
.globl temp_boot_pmds
temp_boot_pmds:
.fill 492,8,0
NEXT_PAGE(level2_kernel_pgt)
/* 40MB kernel mapping. The kernel code cannot be bigger than that.
When you change this change KERNEL_TEXT_SIZE in page.h too. */
/* (2^48-(2*1024*1024*1024)-((2^39)*511)-((2^30)*510)) = 0 */
i = 0
.rept 20
.quad i << 21 | 0x183
i = i + 1
.endr
/* Module mapping starts here */
.fill 492,8,0
NEXT_PAGE(level3_physmem_pgt)
.quad phys_level2_kernel_pgt | 0x007 /* so that __va works even before pagetable_init */
.fill 511,8,0
#undef NEXT_PAGE
.data
#ifdef CONFIG_ACPI_SLEEP
.align PAGE_SIZE
ENTRY(wakeup_level4_pgt)
.quad phys_level3_ident_pgt | 0x007
.fill 255,8,0
.quad phys_level3_physmem_pgt | 0x007
.fill 254,8,0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad phys_level3_kernel_pgt | 0x007
#endif
#ifndef CONFIG_HOTPLUG_CPU
__INITDATA
#endif
/*
* This default setting generates an ident mapping at address 0x100000
* and a mapping for the kernel that precisely maps virtual address
* 0xffffffff80000000 to physical address 0x000000. (always using
* 2Mbyte large pages provided by PAE mode)
*/
.align PAGE_SIZE
ENTRY(boot_level4_pgt)
.quad phys_level3_ident_pgt | 0x007
.fill 255,8,0
.quad phys_level3_physmem_pgt | 0x007
.fill 254,8,0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad phys_level3_kernel_pgt | 0x007
.data
.align 16
.globl cpu_gdt_descr
cpu_gdt_descr:
.word gdt_end-cpu_gdt_table-1
gdt:
.quad cpu_gdt_table
#ifdef CONFIG_SMP
.rept NR_CPUS-1
.word 0
.quad 0
.endr
#endif
/* We need valid kernel segments for data and code in long mode too
* IRET will check the segment types kkeil 2000/10/28
* Also sysret mandates a special GDT layout
*/
.section .data.page_aligned, "aw"
.align PAGE_SIZE
/* The TLS descriptors are currently at a different place compared to i386.
Hopefully nobody expects them at a fixed place (Wine?) */
ENTRY(cpu_gdt_table)
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x0 /* unused */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x00cffa000000ffff /* __USER32_CS */
.quad 0x00cff2000000ffff /* __USER_DS, __USER32_DS */
.quad 0x00affa000000ffff /* __USER_CS */
.quad 0x00cf9a000000ffff /* __KERNEL32_CS */
.quad 0,0 /* TSS */
.quad 0,0 /* LDT */
.quad 0,0,0 /* three TLS descriptors */
.quad 0x0000f40000000000 /* node/CPU stored in limit */
gdt_end:
/* asm/segment.h:GDT_ENTRIES must match this */
/* This should be a multiple of the cache line size */
/* GDTs of other CPUs are now dynamically allocated */
/* zero the remaining page */
.fill PAGE_SIZE / 8 - GDT_ENTRIES,8,0
.section .bss, "aw", @nobits
.align L1_CACHE_BYTES
ENTRY(idt_table)
.skip 256 * 16
.section .bss.page_aligned, "aw", @nobits
.align PAGE_SIZE
ENTRY(empty_zero_page)
.skip PAGE_SIZE
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