Commit 4c5023a3 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by H. Peter Anvin
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x86-32: Handle exception table entries during early boot 



If we get an exception during early boot, walk the exception table to
see if we should intercept it.  The main use case for this is to allow
rdmsr_safe()/wrmsr_safe() during CPU initialization.

Since the exception table is currently sorted at runtime, and fairly
late in startup, this code walks the exception table linearly.  We
obviously don't need to worry about modules, however: none have been
loaded at this point.

This patch changes the early IDT setup to look a lot more like x86-64:
we now install handlers for all 32 exception vectors.  The output of
the early exception handler has changed somewhat as it directly
reflects the stack frame of the exception handler, and the stack frame
has been somewhat restructured.

Finally, centralize the code that can and should be run only once.

[ v2: Use early_fixup_exception() instead of linear search ]

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1334794610-5546-6-git-send-email-hpa@zytor.com
parent 9900aa2f

arch/x86/kernel/head_32.S

+129 −94
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
#include <asm/msr-index.h>

#include <asm/cpufeature.h>

#include <asm/percpu.h>

#include <asm/nops.h>



/* Physical address */

#define pa(X) ((X) - __PAGE_OFFSET)
@@ -363,20 +364,15 @@ default_entry: 
	pushl $0

	popfl



#ifdef CONFIG_SMP

	cmpb $0, ready

	jnz checkCPUtype

#endif /* CONFIG_SMP */



/*

 * start system 32-bit setup. We need to re-do some of the things done

 * in 16-bit mode for the "real" operations.

 */

	call setup_idt



checkCPUtype:



	movl $-1,X86_CPUID		#  -1 for no CPUID initially

	movl setup_once_ref,%eax

	andl %eax,%eax

	jz 1f				# Did we do this already?

	call *%eax

1:

	

/* check if it is 486 or 386. */

/*
@@ -384,7 +380,7 @@ checkCPUtype: 
 * apply at our cpl of 0 and the stack ought to be aligned already, and

 * we don't need to preserve eflags.

 */



	movl $-1,X86_CPUID	# -1 for no CPUID initially

	movb $3,X86		# at least 386

	pushfl			# push EFLAGS

	popl %eax		# get EFLAGS
@@ -450,21 +446,6 @@ is386: movl $2,%ecx # set MP 
	movl $(__KERNEL_PERCPU), %eax

	movl %eax,%fs			# set this cpu's percpu



#ifdef CONFIG_CC_STACKPROTECTOR

	/*

	 * The linker can't handle this by relocation.  Manually set

	 * base address in stack canary segment descriptor.

	 */

	cmpb $0,ready

	jne 1f

	movl $gdt_page,%eax

	movl $stack_canary,%ecx

	movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax)

	shrl $16, %ecx

	movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax)

	movb %ch, 8 * GDT_ENTRY_STACK_CANARY + 7(%eax)

1:

#endif

	movl $(__KERNEL_STACK_CANARY),%eax

	movl %eax,%gs
@@ -473,7 +454,6 @@ is386: movl $2,%ecx # set MP 


	cld			# gcc2 wants the direction flag cleared at all times

	pushl $0		# fake return address for unwinder

	movb $1, ready

	jmp *(initial_code)



/*
@@ -495,81 +475,122 @@ check_x87: 
	.byte 0xDB,0xE4		/* fsetpm for 287, ignored by 387 */

	ret



	

#include "verify_cpu.S"



/*

 *  setup_idt

 *  setup_once

 *

 *  sets up a idt with 256 entries pointing to

 *  ignore_int, interrupt gates. It doesn't actually load

 *  idt - that can be done only after paging has been enabled

 *  and the kernel moved to PAGE_OFFSET. Interrupts

 *  are enabled elsewhere, when we can be relatively

 *  sure everything is ok.

 *  The setup work we only want to run on the BSP.

 *

 *  Warning: %esi is live across this function.

 */

setup_idt:

	lea ignore_int,%edx

	movl $(__KERNEL_CS << 16),%eax

	movw %dx,%ax		/* selector = 0x0010 = cs */

	movw $0x8E00,%dx	/* interrupt gate - dpl=0, present */

__INIT

setup_once:

	/*

	 * Set up a idt with 256 entries pointing to ignore_int,

	 * interrupt gates. It doesn't actually load idt - that needs

	 * to be done on each CPU. Interrupts are enabled elsewhere,

	 * when we can be relatively sure everything is ok.

	 */



	lea idt_table,%edi

	mov $256,%ecx

rp_sidt:

	movl $idt_table,%edi

	movl $early_idt_handlers,%eax

	movl $NUM_EXCEPTION_VECTORS,%ecx

1:

	movl %eax,(%edi)

	movl %edx,4(%edi)

	movl %eax,4(%edi)

	/* interrupt gate, dpl=0, present */

	movl $(0x8E000000 + __KERNEL_CS),2(%edi)

	addl $9,%eax

	addl $8,%edi

	dec %ecx

	jne rp_sidt

	loop 1b



.macro	set_early_handler handler,trapno

	lea \handler,%edx

	movl $256 - NUM_EXCEPTION_VECTORS,%ecx

	movl $ignore_int,%edx

	movl $(__KERNEL_CS << 16),%eax

	movw %dx,%ax

	movw %dx,%ax		/* selector = 0x0010 = cs */

	movw $0x8E00,%dx	/* interrupt gate - dpl=0, present */

	lea idt_table,%edi

	movl %eax,8*\trapno(%edi)

	movl %edx,8*\trapno+4(%edi)

.endm

2:

	movl %eax,(%edi)

	movl %edx,4(%edi)

	addl $8,%edi

	loop 2b



	set_early_handler handler=early_divide_err,trapno=0

	set_early_handler handler=early_illegal_opcode,trapno=6

	set_early_handler handler=early_protection_fault,trapno=13

	set_early_handler handler=early_page_fault,trapno=14

#ifdef CONFIG_CC_STACKPROTECTOR

	/*

	 * Configure the stack canary. The linker can't handle this by

	 * relocation.  Manually set base address in stack canary

	 * segment descriptor.

	 */

	movl $gdt_page,%eax

	movl $stack_canary,%ecx

	movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax)

	shrl $16, %ecx

	movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax)

	movb %ch, 8 * GDT_ENTRY_STACK_CANARY + 7(%eax)

#endif



	andl $0,setup_once_ref	/* Once is enough, thanks */

	ret



early_divide_err:

	xor %edx,%edx

	pushl $0	/* fake errcode */

	jmp early_fault

ENTRY(early_idt_handlers)

	# 36(%esp) %eflags

	# 32(%esp) %cs

	# 28(%esp) %eip

	# 24(%rsp) error code

	i = 0

	.rept NUM_EXCEPTION_VECTORS

	.if (EXCEPTION_ERRCODE_MASK >> i) & 1

	ASM_NOP2

	.else

	pushl $0		# Dummy error code, to make stack frame uniform

	.endif

	pushl $i		# 20(%esp) Vector number

	jmp early_idt_handler

	i = i + 1

	.endr

ENDPROC(early_idt_handlers)

	

	/* This is global to keep gas from relaxing the jumps */

ENTRY(early_idt_handler)

	cld

	cmpl $2,%ss:early_recursion_flag

	je hlt_loop

	incl %ss:early_recursion_flag



early_illegal_opcode:

	movl $6,%edx

	pushl $0	/* fake errcode */

	jmp early_fault

	push %eax		# 16(%esp)

	push %ecx		# 12(%esp)

	push %edx		#  8(%esp)

	push %ds		#  4(%esp)

	push %es		#  0(%esp)

	movl $(__KERNEL_DS),%eax

	movl %eax,%ds

	movl %eax,%es



early_protection_fault:

	movl $13,%edx

	jmp early_fault

	cmpl $(__KERNEL_CS),32(%esp)

	jne 10f



early_page_fault:

	movl $14,%edx

	jmp early_fault

	leal 28(%esp),%eax	# Pointer to %eip

	call early_fixup_exception

	andl %eax,%eax

	jnz ex_entry		/* found an exception entry */



early_fault:

	cld

10:

#ifdef CONFIG_PRINTK

	pusha

	movl $(__KERNEL_DS),%eax

	movl %eax,%ds

	movl %eax,%es

	cmpl $2,early_recursion_flag

	je hlt_loop

	incl early_recursion_flag

	xorl %eax,%eax

	movw %ax,2(%esp)	/* clean up the segment values on some cpus */

	movw %ax,6(%esp)

	movw %ax,34(%esp)

	leal  40(%esp),%eax

	pushl %eax		/* %esp before the exception */

	pushl %ebx

	pushl %ebp

	pushl %esi

	pushl %edi

	movl %cr2,%eax

	pushl %eax

	pushl %edx		/* trapno */

	pushl (20+6*4)(%esp)	/* trapno */

	pushl $fault_msg

	call printk

#endif
@@ -578,6 +599,17 @@ hlt_loop: 
	hlt

	jmp hlt_loop



ex_entry:

	pop %es

	pop %ds

	pop %edx

	pop %ecx

	pop %eax

	addl $8,%esp		/* drop vector number and error code */

	decl %ss:early_recursion_flag

	iret

ENDPROC(early_idt_handler)



/* This is the default interrupt "handler" :-) */

	ALIGN

ignore_int:
@@ -611,13 +643,18 @@ ignore_int: 
	popl %eax

#endif

	iret



#include "verify_cpu.S"

ENDPROC(ignore_int)

__INITDATA

	.align 4

early_recursion_flag:

	.long 0



__REFDATA

	.align 4

ENTRY(initial_code)

	.long i386_start_kernel

ENTRY(setup_once_ref)

	.long setup_once



/*

 * BSS section
@@ -670,22 +707,19 @@ ENTRY(initial_page_table) 
ENTRY(stack_start)

	.long init_thread_union+THREAD_SIZE



early_recursion_flag:

	.long 0



ready:	.byte 0



__INITRODATA

int_msg:

	.asciz "Unknown interrupt or fault at: %p %p %p\n"



fault_msg:

/* fault info: */

	.ascii "BUG: Int %d: CR2 %p\n"

/* pusha regs: */

	.ascii "     EDI %p  ESI %p  EBP %p  ESP %p\n"

	.ascii "     EBX %p  EDX %p  ECX %p  EAX %p\n"

/* regs pushed in early_idt_handler: */

	.ascii "     EDI %p  ESI %p  EBP %p  EBX %p\n"

	.ascii "     ESP %p   ES %p   DS %p\n"

	.ascii "     EDX %p  ECX %p  EAX %p\n"

/* fault frame: */

	.ascii "     err %p  EIP %p   CS %p  flg %p\n"

	.ascii "     vec %p  err %p  EIP %p   CS %p  flg %p\n"

	.ascii "Stack: %p %p %p %p %p %p %p %p\n"

	.ascii "       %p %p %p %p %p %p %p %p\n"

	.asciz "       %p %p %p %p %p %p %p %p\n"
@@ -699,6 +733,7 @@ fault_msg: 
 * segment size, and 32-bit linear address value:

 */



	.data

.globl boot_gdt_descr

.globl idt_descr

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