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: H. Peter Anvin <hpa@zytor.com> Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
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H. Peter Anvin
parent
197725de65
commit
34273f41d5
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@ -909,14 +909,27 @@ config VM86
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default y
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depends on X86_32
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---help---
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This option is required by programs like DOSEMU to run 16-bit legacy
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code on X86 processors. It also may be needed by software like
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XFree86 to initialize some video cards via BIOS. Disabling this
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option saves about 6k.
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This option is required by programs like DOSEMU to run
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16-bit real mode legacy code on x86 processors. It also may
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be needed by software like XFree86 to initialize some video
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cards via BIOS. Disabling this option saves about 6K.
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config X86_16BIT
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bool "Enable support for 16-bit segments" if EXPERT
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default y
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---help---
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This option is required by programs like Wine to run 16-bit
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protected mode legacy code on x86 processors. Disabling
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this option saves about 300 bytes on i386, or around 6K text
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plus 16K runtime memory on x86-64,
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config X86_ESPFIX32
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def_bool y
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depends on X86_16BIT && X86_32
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config X86_ESPFIX64
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def_bool y
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depends on X86_64
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depends on X86_16BIT && X86_64
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config TOSHIBA
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tristate "Toshiba Laptop support"
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@ -527,6 +527,7 @@ syscall_exit:
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restore_all:
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TRACE_IRQS_IRET
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restore_all_notrace:
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#ifdef CONFIG_X86_ESPFIX32
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movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS
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# Warning: PT_OLDSS(%esp) contains the wrong/random values if we
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# are returning to the kernel.
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@ -537,6 +538,7 @@ restore_all_notrace:
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cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax
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CFI_REMEMBER_STATE
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je ldt_ss # returning to user-space with LDT SS
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#endif
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restore_nocheck:
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RESTORE_REGS 4 # skip orig_eax/error_code
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irq_return:
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@ -549,6 +551,7 @@ ENTRY(iret_exc)
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.previous
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_ASM_EXTABLE(irq_return,iret_exc)
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#ifdef CONFIG_X86_ESPFIX32
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CFI_RESTORE_STATE
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ldt_ss:
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#ifdef CONFIG_PARAVIRT
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@ -592,6 +595,7 @@ ldt_ss:
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lss (%esp), %esp /* switch to espfix segment */
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CFI_ADJUST_CFA_OFFSET -8
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jmp restore_nocheck
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#endif
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CFI_ENDPROC
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ENDPROC(system_call)
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@ -699,6 +703,7 @@ END(syscall_badsys)
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* the high word of the segment base from the GDT and swiches to the
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* normal stack and adjusts ESP with the matching offset.
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*/
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#ifdef CONFIG_X86_ESPFIX32
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/* fixup the stack */
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mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
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mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
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@ -708,8 +713,10 @@ END(syscall_badsys)
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pushl_cfi %eax
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lss (%esp), %esp /* switch to the normal stack segment */
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CFI_ADJUST_CFA_OFFSET -8
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#endif
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.endm
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.macro UNWIND_ESPFIX_STACK
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#ifdef CONFIG_X86_ESPFIX32
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movl %ss, %eax
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/* see if on espfix stack */
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cmpw $__ESPFIX_SS, %ax
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@ -720,6 +727,7 @@ END(syscall_badsys)
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/* switch to normal stack */
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FIXUP_ESPFIX_STACK
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27:
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#endif
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.endm
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/*
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@ -1350,11 +1358,13 @@ END(debug)
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ENTRY(nmi)
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RING0_INT_FRAME
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ASM_CLAC
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#ifdef CONFIG_X86_ESPFIX32
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pushl_cfi %eax
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movl %ss, %eax
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cmpw $__ESPFIX_SS, %ax
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popl_cfi %eax
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je nmi_espfix_stack
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#endif
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cmpl $ia32_sysenter_target,(%esp)
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je nmi_stack_fixup
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pushl_cfi %eax
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@ -1394,6 +1404,7 @@ nmi_debug_stack_check:
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FIX_STACK 24, nmi_stack_correct, 1
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jmp nmi_stack_correct
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#ifdef CONFIG_X86_ESPFIX32
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nmi_espfix_stack:
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/* We have a RING0_INT_FRAME here.
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*
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@ -1415,6 +1426,7 @@ nmi_espfix_stack:
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lss 12+4(%esp), %esp # back to espfix stack
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CFI_ADJUST_CFA_OFFSET -24
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jmp irq_return
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#endif
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CFI_ENDPROC
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END(nmi)
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@ -1045,8 +1045,10 @@ irq_return:
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* Are we returning to a stack segment from the LDT? Note: in
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* 64-bit mode SS:RSP on the exception stack is always valid.
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*/
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#ifdef CONFIG_X86_ESPFIX64
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testb $4,(SS-RIP)(%rsp)
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jnz irq_return_ldt
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#endif
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irq_return_iret:
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INTERRUPT_RETURN
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@ -1058,6 +1060,7 @@ ENTRY(native_iret)
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_ASM_EXTABLE(native_iret, bad_iret)
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#endif
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#ifdef CONFIG_X86_ESPFIX64
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irq_return_ldt:
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pushq_cfi %rax
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pushq_cfi %rdi
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@ -1081,6 +1084,7 @@ irq_return_ldt:
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movq %rax,%rsp
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popq_cfi %rax
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jmp irq_return_iret
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#endif
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.section .fixup,"ax"
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bad_iret:
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@ -1152,6 +1156,7 @@ END(common_interrupt)
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* modify the stack to make it look like we just entered
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* the #GP handler from user space, similar to bad_iret.
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*/
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#ifdef CONFIG_X86_ESPFIX64
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ALIGN
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__do_double_fault:
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XCPT_FRAME 1 RDI+8
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@ -1177,6 +1182,9 @@ __do_double_fault:
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retq
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CFI_ENDPROC
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END(__do_double_fault)
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#else
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# define __do_double_fault do_double_fault
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#endif
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/*
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* End of kprobes section
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@ -229,6 +229,11 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
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}
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}
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if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
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error = -EINVAL;
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goto out_unlock;
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}
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fill_ldt(&ldt, &ldt_info);
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if (oldmode)
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ldt.avl = 0;
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