4 files changed, 43 insertions, 5 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9a952a572585..956c7702471e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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"
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2780b8f3b96c..98313ffaae6a 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -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)
 
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bffaa986cafc..da0b9bdcc32e 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -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
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index ebc987398923..c37886d759cc 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -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;