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

commit 34273f41d57ee8d854dcd2a1d754cbb546cb548f upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e9641fe7f4632af3207d124acf06da031fe47440..917c1098775b0e244924d9571da089c0627c4717 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -915,14 +915,27 @@ 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 e36c5cf38fde283ed3f4a15e7b209867200e32d4..a0751249d3c1a9c60fd1a481950ef2396c2589e7 100644 (file)
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -525,6 +525,7 @@ 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.
@@ -535,6 +536,7 @@ 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:
@@ -550,6 +552,7 @@ ENTRY(iret_exc)
        .long irq_return,iret_exc
 .previous
 
+#ifdef CONFIG_X86_ESPFIX32
        CFI_RESTORE_STATE
 ldt_ss:
 #ifdef CONFIG_PARAVIRT
@@ -593,6 +596,7 @@ ldt_ss:
        lss (%esp), %esp                /* switch to espfix segment */
        CFI_ADJUST_CFA_OFFSET -8
        jmp restore_nocheck
+#endif
        CFI_ENDPROC
 ENDPROC(system_call)
 
@@ -766,6 +770,7 @@ ENDPROC(ptregs_clone)
  * 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 */
@@ -775,8 +780,10 @@ ENDPROC(ptregs_clone)
        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
@@ -787,6 +794,7 @@ ENDPROC(ptregs_clone)
        /* switch to normal stack */
        FIXUP_ESPFIX_STACK
 27:
+#endif
 .endm
 
 /*
@@ -1318,11 +1326,13 @@ END(debug)
  */
 ENTRY(nmi)
        RING0_INT_FRAME
+#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
@@ -1362,6 +1372,7 @@ 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.
         *
@@ -1383,6 +1394,7 @@ 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 563b5574dbca730b6e108fdb345afaa9e0688cbc..7a4457e91e8e48b6214fca80e742309d4d371cfb 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -904,8 +904,10 @@ 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
@@ -923,6 +925,7 @@ ENTRY(native_iret)
        .previous
 #endif
 
+#ifdef CONFIG_X86_ESPFIX64
 irq_return_ldt:
        pushq_cfi %rax
        pushq_cfi %rdi
@@ -946,6 +949,7 @@ irq_return_ldt:
        movq %rax,%rsp
        popq_cfi %rax
        jmp irq_return_iret
+#endif
 
        .section .fixup,"ax"
 bad_iret:
@@ -1019,6 +1023,7 @@ 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
@@ -1044,6 +1049,9 @@ __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 ebc9873989233dcba13d1fa1af14e3e921959a85..c37886d759ccac2736c36b357cc0f399786f2fb3 100644 (file)
--- 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;