[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, 16 insertions, 41 deletions

diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index 56655ea8d98f..f9bb1f89d687 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -1088,49 +1088,24 @@ fastcall void do_spurious_interrupt_bug(struct pt_regs * regs,
 #endif
 }
 
-fastcall void setup_x86_bogus_stack(unsigned char * stk)
+fastcall unsigned long patch_espfix_desc(unsigned long uesp,
+                                          unsigned long kesp)
 {
-        unsigned long *switch16_ptr, *switch32_ptr;
-        struct pt_regs *regs;
-        unsigned long stack_top, stack_bot;
-        unsigned short iret_frame16_off;
         int cpu = smp_processor_id();
-        /* reserve the space on 32bit stack for the magic switch16 pointer */
-        memmove(stk, stk + 8, sizeof(struct pt_regs));
-        switch16_ptr = (unsigned long *)(stk + sizeof(struct pt_regs));
-        regs = (struct pt_regs *)stk;
-        /* now the switch32 on 16bit stack */
-        stack_bot = (unsigned long)&per_cpu(cpu_16bit_stack, cpu);
-        stack_top = stack_bot + CPU_16BIT_STACK_SIZE;
-        switch32_ptr = (unsigned long *)(stack_top - 8);
-        iret_frame16_off = CPU_16BIT_STACK_SIZE - 8 - 20;
-        /* copy iret frame on 16bit stack */
-        memcpy((void *)(stack_bot + iret_frame16_off), &regs->eip, 20);
-        /* fill in the switch pointers */
-        switch16_ptr[0] = (regs->esp & 0xffff0000) | iret_frame16_off;
-        switch16_ptr[1] = __ESPFIX_SS;
-        switch32_ptr[0] = (unsigned long)stk + sizeof(struct pt_regs) +
-                8 - CPU_16BIT_STACK_SIZE;
-        switch32_ptr[1] = __KERNEL_DS;
-}
-
-fastcall unsigned char * fixup_x86_bogus_stack(unsigned short sp)
-{
-        unsigned long *switch32_ptr;
-        unsigned char *stack16, *stack32;
-        unsigned long stack_top, stack_bot;
-        int len;
-        int cpu = smp_processor_id();
-        stack_bot = (unsigned long)&per_cpu(cpu_16bit_stack, cpu);
-        stack_top = stack_bot + CPU_16BIT_STACK_SIZE;
-        switch32_ptr = (unsigned long *)(stack_top - 8);
-        /* copy the data from 16bit stack to 32bit stack */
-        len = CPU_16BIT_STACK_SIZE - 8 - sp;
-        stack16 = (unsigned char *)(stack_bot + sp);
-        stack32 = (unsigned char *)
-                (switch32_ptr[0] + CPU_16BIT_STACK_SIZE - 8 - len);
-        memcpy(stack32, stack16, len);
-        return stack32;
+        struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
+        struct desc_struct *gdt = (struct desc_struct *)cpu_gdt_descr->address;
+        unsigned long base = (kesp - uesp) & -THREAD_SIZE;
+        unsigned long new_kesp = kesp - base;
+        unsigned long lim_pages = (new_kesp | (THREAD_SIZE - 1)) >> PAGE_SHIFT;
+        __u64 desc = *(__u64 *)&gdt[GDT_ENTRY_ESPFIX_SS];
+        /* Set up base for espfix segment */
+        desc &= 0x00f0ff0000000000ULL;
+        desc |= ((((__u64)base) << 16) & 0x000000ffffff0000ULL) |
+                ((((__u64)base) << 32) & 0xff00000000000000ULL) |
+                ((((__u64)lim_pages) << 32) & 0x000f000000000000ULL) |
+                (lim_pages & 0xffff);
+        *(__u64 *)&gdt[GDT_ENTRY_ESPFIX_SS] = desc;
+        return new_kesp;
 }
 
 /*