releases/3.14.16/x86-espfix-make-it-possible-to-disable-16-bit-support.patch

   1 From 34273f41d57ee8d854dcd2a1d754cbb546cb548f Mon Sep 17 00:00:00 2001
   2 From: "H. Peter Anvin" <hpa@zytor.com>
   3 Date: Sun, 4 May 2014 10:36:22 -0700
   4 Subject: x86, espfix: Make it possible to disable 16-bit support
   5
   6 From: "H. Peter Anvin" <hpa@zytor.com>
   7
   8 commit 34273f41d57ee8d854dcd2a1d754cbb546cb548f upstream.
   9
  10 Embedded systems, which may be very memory-size-sensitive, are
  11 extremely unlikely to ever encounter any 16-bit software, so make it
  12 a CONFIG_EXPERT option to turn off support for any 16-bit software
  13 whatsoever.
  14
  15 Signed-off-by: H. Peter Anvin <hpa@zytor.com>
  16 Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
  17 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  18
  19 ---
  20  arch/x86/Kconfig           |   23 ++++++++++++++++++-----
  21  arch/x86/kernel/entry_32.S |   12 ++++++++++++
  22  arch/x86/kernel/entry_64.S |    8 ++++++++
  23  arch/x86/kernel/ldt.c      |    5 +++++
  24  4 files changed, 43 insertions(+), 5 deletions(-)
  25
  26 --- a/arch/x86/Kconfig
  27 +++ b/arch/x86/Kconfig
  28 @@ -966,14 +966,27 @@ config VM86
  29         default y
  30         depends on X86_32
  31         ---help---
  32 -         This option is required by programs like DOSEMU to run 16-bit legacy
  33 -         code on X86 processors. It also may be needed by software like
  34 -         XFree86 to initialize some video cards via BIOS. Disabling this
  35 -         option saves about 6k.
  36 +         This option is required by programs like DOSEMU to run
  37 +         16-bit real mode legacy code on x86 processors. It also may
  38 +         be needed by software like XFree86 to initialize some video
  39 +         cards via BIOS. Disabling this option saves about 6K.
  40 +
  41 +config X86_16BIT
  42 +       bool "Enable support for 16-bit segments" if EXPERT
  43 +       default y
  44 +       ---help---
  45 +         This option is required by programs like Wine to run 16-bit
  46 +         protected mode legacy code on x86 processors.  Disabling
  47 +         this option saves about 300 bytes on i386, or around 6K text
  48 +         plus 16K runtime memory on x86-64,
  49 +
  50 +config X86_ESPFIX32
  51 +       def_bool y
  52 +       depends on X86_16BIT && X86_32
  53
  54  config X86_ESPFIX64
  55         def_bool y
  56 -       depends on X86_64
  57 +       depends on X86_16BIT && X86_64
  58
  59  config TOSHIBA
  60         tristate "Toshiba Laptop support"
  61 --- a/arch/x86/kernel/entry_32.S
  62 +++ b/arch/x86/kernel/entry_32.S
  63 @@ -529,6 +529,7 @@ syscall_exit:
  64  restore_all:
  65         TRACE_IRQS_IRET
  66  restore_all_notrace:
  67 +#ifdef CONFIG_X86_ESPFIX32
  68         movl PT_EFLAGS(%esp), %eax      # mix EFLAGS, SS and CS
  69         # Warning: PT_OLDSS(%esp) contains the wrong/random values if we
  70         # are returning to the kernel.
  71 @@ -539,6 +540,7 @@ restore_all_notrace:
  72         cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax
  73         CFI_REMEMBER_STATE
  74         je ldt_ss                       # returning to user-space with LDT SS
  75 +#endif
  76  restore_nocheck:
  77         RESTORE_REGS 4                  # skip orig_eax/error_code
  78  irq_return:
  79 @@ -551,6 +553,7 @@ ENTRY(iret_exc)
  80  .previous
  81         _ASM_EXTABLE(irq_return,iret_exc)
  82
  83 +#ifdef CONFIG_X86_ESPFIX32
  84         CFI_RESTORE_STATE
  85  ldt_ss:
  86  #ifdef CONFIG_PARAVIRT
  87 @@ -594,6 +597,7 @@ ldt_ss:
  88         lss (%esp), %esp                /* switch to espfix segment */
  89         CFI_ADJUST_CFA_OFFSET -8
  90         jmp restore_nocheck
  91 +#endif
  92         CFI_ENDPROC
  93  ENDPROC(system_call)
  94
  95 @@ -706,6 +710,7 @@ END(syscall_badsys)
  96   * the high word of the segment base from the GDT and swiches to the
  97   * normal stack and adjusts ESP with the matching offset.
  98   */
  99 +#ifdef CONFIG_X86_ESPFIX32
 100         /* fixup the stack */
 101         mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
 102         mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
 103 @@ -715,8 +720,10 @@ END(syscall_badsys)
 104         pushl_cfi %eax
 105         lss (%esp), %esp                /* switch to the normal stack segment */
 106         CFI_ADJUST_CFA_OFFSET -8
 107 +#endif
 108  .endm
 109  .macro UNWIND_ESPFIX_STACK
 110 +#ifdef CONFIG_X86_ESPFIX32
 111         movl %ss, %eax
 112         /* see if on espfix stack */
 113         cmpw $__ESPFIX_SS, %ax
 114 @@ -727,6 +734,7 @@ END(syscall_badsys)
 115         /* switch to normal stack */
 116         FIXUP_ESPFIX_STACK
 117  27:
 118 +#endif
 119  .endm
 120
 121  /*
 122 @@ -1357,11 +1365,13 @@ END(debug)
 123  ENTRY(nmi)
 124         RING0_INT_FRAME
 125         ASM_CLAC
 126 +#ifdef CONFIG_X86_ESPFIX32
 127         pushl_cfi %eax
 128         movl %ss, %eax
 129         cmpw $__ESPFIX_SS, %ax
 130         popl_cfi %eax
 131         je nmi_espfix_stack
 132 +#endif
 133         cmpl $ia32_sysenter_target,(%esp)
 134         je nmi_stack_fixup
 135         pushl_cfi %eax
 136 @@ -1401,6 +1411,7 @@ nmi_debug_stack_check:
 137         FIX_STACK 24, nmi_stack_correct, 1
 138         jmp nmi_stack_correct
 139
 140 +#ifdef CONFIG_X86_ESPFIX32
 141  nmi_espfix_stack:
 142         /* We have a RING0_INT_FRAME here.
 143          *
 144 @@ -1422,6 +1433,7 @@ nmi_espfix_stack:
 145         lss 12+4(%esp), %esp            # back to espfix stack
 146         CFI_ADJUST_CFA_OFFSET -24
 147         jmp irq_return
 148 +#endif
 149         CFI_ENDPROC
 150  END(nmi)
 151
 152 --- a/arch/x86/kernel/entry_64.S
 153 +++ b/arch/x86/kernel/entry_64.S
 154 @@ -1045,8 +1045,10 @@ irq_return:
 155          * Are we returning to a stack segment from the LDT?  Note: in
 156          * 64-bit mode SS:RSP on the exception stack is always valid.
 157          */
 158 +#ifdef CONFIG_X86_ESPFIX64
 159         testb $4,(SS-RIP)(%rsp)
 160         jnz irq_return_ldt
 161 +#endif
 162
 163  irq_return_iret:
 164         INTERRUPT_RETURN
 165 @@ -1058,6 +1060,7 @@ ENTRY(native_iret)
 166         _ASM_EXTABLE(native_iret, bad_iret)
 167  #endif
 168
 169 +#ifdef CONFIG_X86_ESPFIX64
 170  irq_return_ldt:
 171         pushq_cfi %rax
 172         pushq_cfi %rdi
 173 @@ -1081,6 +1084,7 @@ irq_return_ldt:
 174         movq %rax,%rsp
 175         popq_cfi %rax
 176         jmp irq_return_iret
 177 +#endif
 178
 179         .section .fixup,"ax"
 180  bad_iret:
 181 @@ -1152,6 +1156,7 @@ END(common_interrupt)
 182          * modify the stack to make it look like we just entered
 183          * the #GP handler from user space, similar to bad_iret.
 184          */
 185 +#ifdef CONFIG_X86_ESPFIX64
 186         ALIGN
 187  __do_double_fault:
 188         XCPT_FRAME 1 RDI+8
 189 @@ -1177,6 +1182,9 @@ __do_double_fault:
 190         retq
 191         CFI_ENDPROC
 192  END(__do_double_fault)
 193 +#else
 194 +# define __do_double_fault do_double_fault
 195 +#endif
 196
 197  /*
 198   * End of kprobes section
 199 --- a/arch/x86/kernel/ldt.c
 200 +++ b/arch/x86/kernel/ldt.c
 201 @@ -229,6 +229,11 @@ static int write_ldt(void __user *ptr, u
 202                 }
 203         }
 204
 205 +       if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
 206 +               error = -EINVAL;
 207 +               goto out_unlock;
 208 +       }
 209 +
 210         fill_ldt(&ldt, &ldt_info);
 211         if (oldmode)
 212                 ldt.avl = 0;