[Xen-devel] [patch 4/8] Replace sensitive instructions with macros.

[Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>]

Abstract sensitive instructions in assembler code, replacing them with
macros (which currently are #defined to the native versions).  We use
long names: assembler is case-insensitive, so if something goes wrong
and macros do not expand, it would assemble anyway.

Resulting object files are exactly the same as before.

Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>

---
 arch/i386/kernel/entry.S    |   38 ++++++++++++++++++++++----------------
 include/asm-i386/spinlock.h |    7 +++++--
 2 files changed, 27 insertions(+), 18 deletions(-)


===================================================================
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -76,8 +76,15 @@ NT_MASK              = 0x00004000
 NT_MASK                = 0x00004000
 VM_MASK                = 0x00020000
 
+/* These are replaces for paravirtualization */
+#define DISABLE_INTERRUPTS             cli
+#define ENABLE_INTERRUPTS              sti
+#define ENABLE_INTERRUPTS_SYSEXIT      sti; sysexit
+#define INTERRUPT_RETURN               iret
+#define GET_CR0_INTO_EAX               movl %cr0, %eax
+
 #ifdef CONFIG_PREEMPT
-#define preempt_stop           cli; TRACE_IRQS_OFF
+#define preempt_stop           DISABLE_INTERRUPTS; TRACE_IRQS_OFF
 #else
 #define preempt_stop
 #define resume_kernel          restore_nocheck
@@ -233,7 +240,7 @@ check_userspace:
        cmpl $SEGMENT_RPL_MASK, %eax
        jb resume_kernel                # not returning to v8086 or userspace
 ENTRY(resume_userspace)
-       cli                             # make sure we don't miss an interrupt
+       DISABLE_INTERRUPTS              # make sure we don't miss an interrupt
                                        # setting need_resched or sigpending
                                        # between sampling and the iret
        movl TI_flags(%ebp), %ecx
@@ -244,7 +251,7 @@ ENTRY(resume_userspace)
 
 #ifdef CONFIG_PREEMPT
 ENTRY(resume_kernel)
-       cli
+       DISABLE_INTERRUPTS
        cmpl $0,TI_preempt_count(%ebp)  # non-zero preempt_count ?
        jnz restore_nocheck
 need_resched:
@@ -272,7 +279,7 @@ sysenter_past_esp:
         * No need to follow this irqs on/off section: the syscall
         * disabled irqs and here we enable it straight after entry:
         */
-       sti
+       ENABLE_INTERRUPTS
        pushl $(__USER_DS)
        CFI_ADJUST_CFA_OFFSET 4
        /*CFI_REL_OFFSET ss, 0*/
@@ -317,7 +324,7 @@ 1:  movl (%ebp),%ebp
        jae syscall_badsys
        call *sys_call_table(,%eax,4)
        movl %eax,EAX(%esp)
-       cli
+       DISABLE_INTERRUPTS
        TRACE_IRQS_OFF
        movl TI_flags(%ebp), %ecx
        testw $_TIF_ALLWORK_MASK, %cx
@@ -327,8 +334,7 @@ 1:  movl (%ebp),%ebp
        movl OLDESP(%esp), %ecx
        xorl %ebp,%ebp
        TRACE_IRQS_ON
-       sti
-       sysexit
+       ENABLE_INTERRUPTS_SYSEXIT
        CFI_ENDPROC
 
 
@@ -353,7 +359,7 @@ syscall_call:
        call *sys_call_table(,%eax,4)
        movl %eax,EAX(%esp)             # store the return value
 syscall_exit:
-       cli                             # make sure we don't miss an interrupt
+       DISABLE_INTERRUPTS              # make sure we don't miss an interrupt
                                        # setting need_resched or sigpending
                                        # between sampling and the iret
        TRACE_IRQS_OFF
@@ -378,11 +384,11 @@ restore_nocheck_notrace:
        RESTORE_REGS
        addl $4, %esp
        CFI_ADJUST_CFA_OFFSET -4
-1:     iret
+1:     INTERRUPT_RETURN
 .section .fixup,"ax"
 iret_exc:
        TRACE_IRQS_ON
-       sti
+       ENABLE_INTERRUPTS
        pushl $0                        # no error code
        pushl $do_iret_error
        jmp error_code
@@ -406,7 +412,7 @@ ldt_ss:
         * dosemu and wine happy. */
        subl $8, %esp           # reserve space for switch16 pointer
        CFI_ADJUST_CFA_OFFSET 8
-       cli
+       DISABLE_INTERRUPTS
        TRACE_IRQS_OFF
        movl %esp, %eax
        /* Set up the 16bit stack frame with switch32 pointer on top,
@@ -416,7 +422,7 @@ ldt_ss:
        TRACE_IRQS_IRET
        RESTORE_REGS
        lss 20+4(%esp), %esp    # switch to 16bit stack
-1:     iret
+1:     INTERRUPT_RETURN
 .section __ex_table,"a"
        .align 4
        .long 1b,iret_exc
@@ -431,7 +437,7 @@ work_pending:
        jz work_notifysig
 work_resched:
        call schedule
-       cli                             # make sure we don't miss an interrupt
+       DISABLE_INTERRUPTS              # make sure we don't miss an interrupt
                                        # setting need_resched or sigpending
                                        # between sampling and the iret
        TRACE_IRQS_OFF
@@ -487,7 +493,7 @@ syscall_exit_work:
        testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP), %cl
        jz work_pending
        TRACE_IRQS_ON
-       sti                             # could let do_syscall_trace() call
+       ENABLE_INTERRUPTS               # could let do_syscall_trace() call
                                        # schedule() instead
        movl %esp, %eax
        movl $1, %edx
@@ -666,7 +672,7 @@ ENTRY(device_not_available)
        pushl $-1                       # mark this as an int
        CFI_ADJUST_CFA_OFFSET 4
        SAVE_ALL
-       movl %cr0, %eax
+       GET_CR0_INTO_EAX
        testl $0x4, %eax                # EM (math emulation bit)
        jne device_not_available_emulate
        preempt_stop
@@ -796,7 +802,7 @@ nmi_16bit_stack:
        call do_nmi
        RESTORE_REGS
        lss 12+4(%esp), %esp            # back to 16bit stack
-1:     iret
+1:     INTERRUPT_RETURN
        CFI_ENDPROC
 .section __ex_table,"a"
        .align 4
===================================================================
--- a/include/asm-i386/spinlock.h
+++ b/include/asm-i386/spinlock.h
@@ -16,6 +16,9 @@
  *
  * (the type definitions are in asm/spinlock_types.h)
  */
+
+#define CLI_STRING     "cli"
+#define STI_STRING     "sti"
 
 #define __raw_spin_is_locked(x) \
                (*(volatile signed char *)(&(x)->slock) <= 0)
@@ -43,12 +46,12 @@
        "2:\t" \
        "testl $0x200, %1\n\t" \
        "jz 4f\n\t" \
-       "sti\n" \
+       STI_STRING "\n" \
        "3:\t" \
        "rep;nop\n\t" \
        "cmpb $0, %0\n\t" \
        "jle 3b\n\t" \
-       "cli\n\t" \
+       CLI_STRING "\n\t" \
        "jmp 1b\n" \
        "4:\t" \
        "rep;nop\n\t" \

--


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