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Commit 34273f41 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86, espfix: Make it possible to disable 16-bit support 



Embedded systems, which may be very memory-size-sensitive, are
extremely unlikely to ever encounter any 16-bit software, so make it
a CONFIG_EXPERT option to turn off support for any 16-bit software
whatsoever.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
parent 197725de

arch/x86/Kconfig

+18 −5
Original line number Diff line number Diff line
@@ -909,14 +909,27 @@ config VM86 
	default y

	depends on X86_32

	---help---

	  This option is required by programs like DOSEMU to run 16-bit legacy

	  code on X86 processors. It also may be needed by software like

	  XFree86 to initialize some video cards via BIOS. Disabling this

	  option saves about 6k.

	  This option is required by programs like DOSEMU to run

	  16-bit real mode legacy code on x86 processors. It also may

	  be needed by software like XFree86 to initialize some video

	  cards via BIOS. Disabling this option saves about 6K.



config X86_16BIT

	bool "Enable support for 16-bit segments" if EXPERT

	default y

	---help---

	  This option is required by programs like Wine to run 16-bit

	  protected mode legacy code on x86 processors.  Disabling

	  this option saves about 300 bytes on i386, or around 6K text

	  plus 16K runtime memory on x86-64,



config X86_ESPFIX32

	def_bool y

	depends on X86_16BIT && X86_32



config X86_ESPFIX64

	def_bool y

	depends on X86_64

	depends on X86_16BIT && X86_64



config TOSHIBA

	tristate "Toshiba Laptop support"

arch/x86/kernel/entry_32.S

+12 −0
Original line number Diff line number Diff line
@@ -527,6 +527,7 @@ syscall_exit: 
restore_all:

	TRACE_IRQS_IRET

restore_all_notrace:

#ifdef CONFIG_X86_ESPFIX32

	movl PT_EFLAGS(%esp), %eax	# mix EFLAGS, SS and CS

	# Warning: PT_OLDSS(%esp) contains the wrong/random values if we

	# are returning to the kernel.
@@ -537,6 +538,7 @@ restore_all_notrace: 
	cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax

	CFI_REMEMBER_STATE

	je ldt_ss			# returning to user-space with LDT SS

#endif

restore_nocheck:

	RESTORE_REGS 4			# skip orig_eax/error_code

irq_return:
@@ -549,6 +551,7 @@ ENTRY(iret_exc) 
.previous

	_ASM_EXTABLE(irq_return,iret_exc)



#ifdef CONFIG_X86_ESPFIX32

	CFI_RESTORE_STATE

ldt_ss:

#ifdef CONFIG_PARAVIRT
@@ -592,6 +595,7 @@ ldt_ss: 
	lss (%esp), %esp		/* switch to espfix segment */

	CFI_ADJUST_CFA_OFFSET -8

	jmp restore_nocheck

#endif

	CFI_ENDPROC

ENDPROC(system_call)
@@ -699,6 +703,7 @@ END(syscall_badsys) 
 * the high word of the segment base from the GDT and swiches to the

 * normal stack and adjusts ESP with the matching offset.

 */

#ifdef CONFIG_X86_ESPFIX32

	/* fixup the stack */

	mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */

	mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
@@ -708,8 +713,10 @@ END(syscall_badsys) 
	pushl_cfi %eax

	lss (%esp), %esp		/* switch to the normal stack segment */

	CFI_ADJUST_CFA_OFFSET -8

#endif

.endm

.macro UNWIND_ESPFIX_STACK

#ifdef CONFIG_X86_ESPFIX32

	movl %ss, %eax

	/* see if on espfix stack */

	cmpw $__ESPFIX_SS, %ax
@@ -720,6 +727,7 @@ END(syscall_badsys) 
	/* switch to normal stack */

	FIXUP_ESPFIX_STACK

27:

#endif

.endm



/*
@@ -1350,11 +1358,13 @@ END(debug) 
ENTRY(nmi)

	RING0_INT_FRAME

	ASM_CLAC

#ifdef CONFIG_X86_ESPFIX32

	pushl_cfi %eax

	movl %ss, %eax

	cmpw $__ESPFIX_SS, %ax

	popl_cfi %eax

	je nmi_espfix_stack

#endif

	cmpl $ia32_sysenter_target,(%esp)

	je nmi_stack_fixup

	pushl_cfi %eax
@@ -1394,6 +1404,7 @@ nmi_debug_stack_check: 
	FIX_STACK 24, nmi_stack_correct, 1

	jmp nmi_stack_correct



#ifdef CONFIG_X86_ESPFIX32

nmi_espfix_stack:

	/* We have a RING0_INT_FRAME here.

	 *
@@ -1415,6 +1426,7 @@ nmi_espfix_stack: 
	lss 12+4(%esp), %esp		# back to espfix stack

	CFI_ADJUST_CFA_OFFSET -24

	jmp irq_return

#endif

	CFI_ENDPROC

END(nmi)

arch/x86/kernel/entry_64.S

+8 −0
Original line number Diff line number Diff line
@@ -1045,8 +1045,10 @@ irq_return: 
	 * Are we returning to a stack segment from the LDT?  Note: in

	 * 64-bit mode SS:RSP on the exception stack is always valid.

	 */

#ifdef CONFIG_X86_ESPFIX64

	testb $4,(SS-RIP)(%rsp)

	jnz irq_return_ldt

#endif



irq_return_iret:

	INTERRUPT_RETURN
@@ -1058,6 +1060,7 @@ ENTRY(native_iret) 
	_ASM_EXTABLE(native_iret, bad_iret)

#endif



#ifdef CONFIG_X86_ESPFIX64

irq_return_ldt:

	pushq_cfi %rax

	pushq_cfi %rdi
@@ -1081,6 +1084,7 @@ irq_return_ldt: 
	movq %rax,%rsp

	popq_cfi %rax

	jmp irq_return_iret

#endif



	.section .fixup,"ax"

bad_iret:
@@ -1152,6 +1156,7 @@ END(common_interrupt) 
	 * modify the stack to make it look like we just entered

	 * the #GP handler from user space, similar to bad_iret.

	 */

#ifdef CONFIG_X86_ESPFIX64

	ALIGN

__do_double_fault:

	XCPT_FRAME 1 RDI+8
@@ -1177,6 +1182,9 @@ __do_double_fault: 
	retq

	CFI_ENDPROC

END(__do_double_fault)

#else

# define __do_double_fault do_double_fault

#endif



/*

 * End of kprobes section

arch/x86/kernel/ldt.c

+5 −0
Original line number Diff line number Diff line
@@ -229,6 +229,11 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) 
		}

	}



	if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {

		error = -EINVAL;

		goto out_unlock;

	}



	fill_ldt(&ldt, &ldt_info);

	if (oldmode)

		ldt.avl = 0;