[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>

7 files changed, 103 insertions, 97 deletions

diff --git a/arch/i386/kernel/asm-offsets.c b/arch/i386/kernel/asm-offsets.c
index c80271f8f084..e94d910a28bd 100644
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -58,6 +58,11 @@ void foo(void)
         OFFSET(TI_sysenter_return, thread_info, sysenter_return);
         BLANK();
 
+        OFFSET(GDS_size, Xgt_desc_struct, size);
+        OFFSET(GDS_address, Xgt_desc_struct, address);
+        OFFSET(GDS_pad, Xgt_desc_struct, pad);
+        BLANK();
+
         OFFSET(EXEC_DOMAIN_handler, exec_domain, handler);
         OFFSET(RT_SIGFRAME_sigcontext, rt_sigframe, uc.uc_mcontext);
         BLANK();
diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index d9f3e3c31f05..5532fc4e1bf0 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -24,9 +24,6 @@
 DEFINE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr);
 EXPORT_PER_CPU_SYMBOL(cpu_gdt_descr);
 
-DEFINE_PER_CPU(unsigned char, cpu_16bit_stack[CPU_16BIT_STACK_SIZE]);
-EXPORT_PER_CPU_SYMBOL(cpu_16bit_stack);
-
 static int cachesize_override __cpuinitdata = -1;
 static int disable_x86_fxsr __cpuinitdata;
 static int disable_x86_serial_nr __cpuinitdata = 1;
@@ -603,7 +600,6 @@ void __cpuinit cpu_init(void)
         struct tss_struct * t = &per_cpu(init_tss, cpu);
         struct thread_struct *thread = &current->thread;
         struct desc_struct *gdt;
-        __u32 stk16_off = (__u32)&per_cpu(cpu_16bit_stack, cpu);
         struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
         if (cpu_test_and_set(cpu, cpu_initialized)) {
@@ -651,13 +647,6 @@ old_gdt:
          * and set up the GDT descriptor:
          */
         memcpy(gdt, cpu_gdt_table, GDT_SIZE);
-
-        /* Set up GDT entry for 16bit stack */
-        *(__u64 *)(&gdt[GDT_ENTRY_ESPFIX_SS]) |=
-                ((((__u64)stk16_off) << 16) & 0x000000ffffff0000ULL) |
-                ((((__u64)stk16_off) << 32) & 0xff00000000000000ULL) |
-                (CPU_16BIT_STACK_SIZE - 1);
-
         cpu_gdt_descr->size = GDT_SIZE - 1;
         cpu_gdt_descr->address = (unsigned long)gdt;
 
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"
diff --git a/arch/i386/kernel/head.S b/arch/i386/kernel/head.S
index ca31f18d277c..b1f1df11fcc6 100644
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -584,7 +584,7 @@ ENTRY(cpu_gdt_table)
         .quad 0x00009a000000ffff        /* 0xc0 APM CS 16 code (16 bit) */
         .quad 0x004092000000ffff        /* 0xc8 APM DS    data */
 
-        .quad 0x0000920000000000        /* 0xd0 - ESPFIX 16-bit SS */
+        .quad 0x00c0920000000000        /* 0xd0 - ESPFIX SS */
         .quad 0x0000000000000000        /* 0xd8 - unused */
         .quad 0x0000000000000000        /* 0xe0 - unused */
         .quad 0x0000000000000000        /* 0xe8 - unused */
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;
 }
 
 /*
diff --git a/include/asm-i386/desc.h b/include/asm-i386/desc.h
index a0398f780ca1..6cf2ac2bfde7 100644
--- a/include/asm-i386/desc.h
+++ b/include/asm-i386/desc.h
@@ -4,8 +4,6 @@
 #include <asm/ldt.h>
 #include <asm/segment.h>
 
-#define CPU_16BIT_STACK_SIZE 1024
-
 #ifndef __ASSEMBLY__
 
 #include <linux/preempt.h>
@@ -16,8 +14,6 @@
 
 extern struct desc_struct cpu_gdt_table[GDT_ENTRIES];
 
-DECLARE_PER_CPU(unsigned char, cpu_16bit_stack[CPU_16BIT_STACK_SIZE]);
-
 struct Xgt_desc_struct {
         unsigned short size;
         unsigned long address __attribute__((packed));
@@ -181,6 +177,29 @@ static inline unsigned long get_desc_base(unsigned long *desc)
         return base;
 }
 
+#else /* __ASSEMBLY__ */
+
+/*
+ * GET_DESC_BASE reads the descriptor base of the specified segment.
+ *
+ * Args:
+ *    idx - descriptor index
+ *    gdt - GDT pointer
+ *    base - 32bit register to which the base will be written
+ *    lo_w - lo word of the "base" register
+ *    lo_b - lo byte of the "base" register
+ *    hi_b - hi byte of the low word of the "base" register
+ *
+ * Example:
+ *    GET_DESC_BASE(GDT_ENTRY_ESPFIX_SS, %ebx, %eax, %ax, %al, %ah)
+ *    Will read the base address of GDT_ENTRY_ESPFIX_SS and put it into %eax.
+ */
+#define GET_DESC_BASE(idx, gdt, base, lo_w, lo_b, hi_b) \
+        movb idx*8+4(gdt), lo_b; \
+        movb idx*8+7(gdt), hi_b; \
+        shll $16, base; \
+        movw idx*8+2(gdt), lo_w;
+
 #endif /* !__ASSEMBLY__ */
 
 #endif
diff --git a/include/asm-i386/percpu.h b/include/asm-i386/percpu.h
index 5764afa4b6a4..510ae1d3486c 100644
--- a/include/asm-i386/percpu.h
+++ b/include/asm-i386/percpu.h
@@ -1,6 +1,31 @@
 #ifndef __ARCH_I386_PERCPU__
 #define __ARCH_I386_PERCPU__
 
+#ifndef __ASSEMBLY__
 #include <asm-generic/percpu.h>
+#else
+
+/*
+ * PER_CPU finds an address of a per-cpu variable.
+ *
+ * Args:
+ *    var - variable name
+ *    cpu - 32bit register containing the current CPU number
+ *
+ * The resulting address is stored in the "cpu" argument.
+ *
+ * Example:
+ *    PER_CPU(cpu_gdt_descr, %ebx)
+ */
+#ifdef CONFIG_SMP
+#define PER_CPU(var, cpu) \
+        movl __per_cpu_offset(,cpu,4), cpu;     \
+        addl $per_cpu__/**/var, cpu;
+#else /* ! SMP */
+#define PER_CPU(var, cpu) \
+        movl $per_cpu__/**/var, cpu;
+#endif  /* SMP */
+
+#endif /* !__ASSEMBLY__ */
 
 #endif /* __ARCH_I386_PERCPU__ */