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
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bffaa98..da0b9bd 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1045,8 +1045,10 @@
* 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 @@
_ASM_EXTABLE(native_iret, bad_iret)
#endif
+#ifdef CONFIG_X86_ESPFIX64
irq_return_ldt:
pushq_cfi %rax
pushq_cfi %rdi
@@ -1081,6 +1084,7 @@
movq %rax,%rsp
popq_cfi %rax
jmp irq_return_iret
+#endif
.section .fixup,"ax"
bad_iret:
@@ -1152,6 +1156,7 @@
* 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 @@
retq
CFI_ENDPROC
END(__do_double_fault)
+#else
+# define __do_double_fault do_double_fault
+#endif
/*
* End of kprobes section