[PATCH] i386: espfix cleanup

Clean up the espfix code:

- Introduced PER_CPU() macro to be used from asm
- Introduced GET_DESC_BASE() macro to be used from asm
- Rewrote the fixup code in asm, as calling a C code with the altered %ss
  appeared to be unsafe
- No longer altering the stack from a .fixup section
- 16bit per-cpu stack is no longer used, instead the stack segment base
  is patched the way so that the high word of the kernel and user %esp
  are the same.
- Added the limit-patching for the espfix segment. (Chuck Ebbert)

[jeremy@goop.org: use the x86 scaling addressing mode rather than shifting]
Signed-off-by: Stas Sergeev <stsp@aknet.ru>
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Zachary Amsden <zach@vmware.com>
Acked-by: Chuck Ebbert <76306.1226@compuserve.com>
Acked-by: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 33 insertions, 40 deletions

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 5a63d6fdb70e..c38d801ba0bb 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -48,6 +48,7 @@
 #include <asm/smp.h>
 #include <asm/page.h>
 #include <asm/desc.h>
+#include <asm/percpu.h>
 #include <asm/dwarf2.h>
 #include "irq_vectors.h"
 
@@ -418,23 +419,18 @@ ldt_ss:
          * This is an "official" bug of all the x86-compatible
          * CPUs, which we can try to work around to make
          * dosemu and wine happy. */
-        subl $8, %esp           # reserve space for switch16 pointer
-        CFI_ADJUST_CFA_OFFSET 8
+        movl OLDESP(%esp), %eax
+        movl %esp, %edx
+        call patch_espfix_desc
+        pushl $__ESPFIX_SS
+        CFI_ADJUST_CFA_OFFSET 4
+        pushl %eax
+        CFI_ADJUST_CFA_OFFSET 4
         DISABLE_INTERRUPTS
         TRACE_IRQS_OFF
-        movl %esp, %eax
-        /* Set up the 16bit stack frame with switch32 pointer on top,
-         * and a switch16 pointer on top of the current frame. */
-        call setup_x86_bogus_stack
-        CFI_ADJUST_CFA_OFFSET -8        # frame has moved
-        TRACE_IRQS_IRET
-        RESTORE_REGS
-        lss 20+4(%esp), %esp    # switch to 16bit stack
-1:      INTERRUPT_RETURN
-.section __ex_table,"a"
-        .align 4
-        .long 1b,iret_exc
-.previous
+        lss (%esp), %esp
+        CFI_ADJUST_CFA_OFFSET -8
+        jmp restore_nocheck
         CFI_ENDPROC
 
         # perform work that needs to be done immediately before resumption
@@ -524,30 +520,30 @@ syscall_badsys:
         CFI_ENDPROC
 
 #define FIXUP_ESPFIX_STACK \
-        movl %esp, %eax; \
-        /* switch to 32bit stack using the pointer on top of 16bit stack */ \
-        lss %ss:CPU_16BIT_STACK_SIZE-8, %esp; \
-        /* copy data from 16bit stack to 32bit stack */ \
-        call fixup_x86_bogus_stack; \
-        /* put ESP to the proper location */ \
-        movl %eax, %esp;
-#define UNWIND_ESPFIX_STACK \
+        /* since we are on a wrong stack, we cant make it a C code :( */ \
+        GET_THREAD_INFO(%ebp); \
+        movl TI_cpu(%ebp), %ebx; \
+        PER_CPU(cpu_gdt_descr, %ebx); \
+        movl GDS_address(%ebx), %ebx; \
+        GET_DESC_BASE(GDT_ENTRY_ESPFIX_SS, %ebx, %eax, %ax, %al, %ah); \
+        addl %esp, %eax; \
+        pushl $__KERNEL_DS; \
+        CFI_ADJUST_CFA_OFFSET 4; \
         pushl %eax; \
         CFI_ADJUST_CFA_OFFSET 4; \
+        lss (%esp), %esp; \
+        CFI_ADJUST_CFA_OFFSET -8;
+#define UNWIND_ESPFIX_STACK \
         movl %ss, %eax; \
-        /* see if on 16bit stack */ \
+        /* see if on espfix stack */ \
         cmpw $__ESPFIX_SS, %ax; \
-        je 28f; \
-27:     popl %eax; \
-        CFI_ADJUST_CFA_OFFSET -4; \
-.section .fixup,"ax"; \
-28:     movl $__KERNEL_DS, %eax; \
+        jne 27f; \
+        movl $__KERNEL_DS, %eax; \
         movl %eax, %ds; \
         movl %eax, %es; \
-        /* switch to 32bit stack */ \
+        /* switch to normal stack */ \
         FIXUP_ESPFIX_STACK; \
-        jmp 27b; \
-.previous
+27:;
 
 /*
  * Build the entry stubs and pointer table with
@@ -614,7 +610,6 @@ error_code:
         pushl %eax
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET eax, 0
-        xorl %eax, %eax
         pushl %ebp
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET ebp, 0
@@ -627,7 +622,6 @@ error_code:
         pushl %edx
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET edx, 0
-        decl %eax                       # eax = -1
         pushl %ecx
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET ecx, 0
@@ -644,7 +638,7 @@ error_code:
         /*CFI_REGISTER es, ecx*/
         movl ES(%esp), %edi             # get the function address
         movl ORIG_EAX(%esp), %edx       # get the error code
-        movl %eax, ORIG_EAX(%esp)
+        movl $-1, ORIG_EAX(%esp)
         movl %ecx, ES(%esp)
         /*CFI_REL_OFFSET es, ES*/
         movl $(__USER_DS), %ecx
@@ -754,7 +748,7 @@ KPROBE_ENTRY(nmi)
         cmpw $__ESPFIX_SS, %ax
         popl %eax
         CFI_ADJUST_CFA_OFFSET -4
-        je nmi_16bit_stack
+        je nmi_espfix_stack
         cmpl $sysenter_entry,(%esp)
         je nmi_stack_fixup
         pushl %eax
@@ -797,7 +791,7 @@ nmi_debug_stack_check:
         FIX_STACK(24,nmi_stack_correct, 1)
         jmp nmi_stack_correct
 
-nmi_16bit_stack:
+nmi_espfix_stack:
         /* We have a RING0_INT_FRAME here.
          *
          * create the pointer to lss back
@@ -806,7 +800,6 @@ nmi_16bit_stack:
         CFI_ADJUST_CFA_OFFSET 4
         pushl %esp
         CFI_ADJUST_CFA_OFFSET 4
-        movzwl %sp, %esp
         addw $4, (%esp)
         /* copy the iret frame of 12 bytes */
         .rept 3
@@ -817,11 +810,11 @@ nmi_16bit_stack:
         CFI_ADJUST_CFA_OFFSET 4
         SAVE_ALL
         FIXUP_ESPFIX_STACK              # %eax == %esp
-        CFI_ADJUST_CFA_OFFSET -20       # the frame has now moved
         xorl %edx,%edx                  # zero error code
         call do_nmi
         RESTORE_REGS
-        lss 12+4(%esp), %esp            # back to 16bit stack
+        lss 12+4(%esp), %esp            # back to espfix stack
+        CFI_ADJUST_CFA_OFFSET -24
 1:      INTERRUPT_RETURN
         CFI_ENDPROC
 .section __ex_table,"a"