[PATCH] 7/8 Create accessors that allow the i386 kernel to run at CPLs 0-2

[Zachary Amsden <zach@vmware.com>]

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i386 Transparent paravirtualization subarch patch #7.

These changes allow a sub-architecture to change the notion of privilege
by running the kernel at CPL 0, 1, or 2.  The make_kernel_segment() macro
can be redefined by a subarchitecture to change the RPL on kernel segments
to the appropriate value, and the tests user_mode() and user_mode_vm()
may be similarly overridden.

Changes to the assembly code are required to fully support this, and
provided in a separate patch.

Diffs against: 2.6.13-rc4-mm1

Signed-off-by: Zachary Amsden <zach@vmware.com>
Index: linux-2.6.13/arch/i386/kernel/process.c
===================================================================
--- linux-2.6.13.orig/arch/i386/kernel/process.c	2005-08-03 23:37:25.000000000 -0700
+++ linux-2.6.13/arch/i386/kernel/process.c	2005-08-04 10:04:42.000000000 -0700
@@ -356,7 +356,7 @@
 	regs.xes = __USER_DS;
 	regs.orig_eax = -1;
 	regs.eip = (unsigned long) kernel_thread_helper;
-	regs.xcs = __KERNEL_CS;
+	regs.xcs = make_kernel_segment(__KERNEL_CS);
 	regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
 
 	/* Ok, create the new process.. */
Index: linux-2.6.13/arch/i386/kernel/traps.c
===================================================================
--- linux-2.6.13.orig/arch/i386/kernel/traps.c	2005-08-03 23:36:46.000000000 -0700
+++ linux-2.6.13/arch/i386/kernel/traps.c	2005-08-04 10:04:42.000000000 -0700
@@ -1025,10 +1025,10 @@
 	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;
+	switch16_ptr[1] = make_kernel_segment(__ESPFIX_SS);
 	switch32_ptr[0] = (unsigned long)stk + sizeof(struct pt_regs) +
 		8 - CPU_16BIT_STACK_SIZE;
-	switch32_ptr[1] = __KERNEL_DS;
+	switch32_ptr[1] = make_kernel_segment(__KERNEL_DS);
 }
 
 fastcall unsigned char * fixup_x86_bogus_stack(unsigned short sp)
Index: linux-2.6.13/include/asm-i386/ptrace.h
===================================================================
--- linux-2.6.13.orig/include/asm-i386/ptrace.h	2005-08-03 23:36:46.000000000 -0700
+++ linux-2.6.13/include/asm-i386/ptrace.h	2005-08-04 10:04:42.000000000 -0700
@@ -57,25 +57,11 @@
 #ifdef __KERNEL__
 
 #include <asm/vm86.h>
+#include <mach_segment.h>
 
 struct task_struct;
 extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);
 
-/*
- * user_mode_vm(regs) determines whether a register set came from user mode.
- * This is true if V8086 mode was enabled OR if the register set was from
- * protected mode with RPL-3 CS value.  This tricky test checks that with
- * one comparison.  Many places in the kernel can bypass this full check
- * if they have already ruled out V8086 mode, so user_mode(regs) can be used.
- */
-static inline int user_mode(struct pt_regs *regs)
-{
-	return (regs->xcs & 3) != 0;
-}
-static inline int user_mode_vm(struct pt_regs *regs)
-{
-	return ((regs->xcs & 3) | (regs->eflags & VM_MASK)) != 0;
-}
 #define instruction_pointer(regs) ((regs)->eip)
 #if defined(CONFIG_SMP) && defined(CONFIG_FRAME_POINTER)
 extern unsigned long profile_pc(struct pt_regs *regs);
Index: linux-2.6.13/include/asm-i386/mach-default/mach_segment.h
===================================================================
--- linux-2.6.13.orig/include/asm-i386/mach-default/mach_segment.h	2005-08-04 10:04:42.000000000 -0700
+++ linux-2.6.13/include/asm-i386/mach-default/mach_segment.h	2005-08-04 10:05:17.000000000 -0700
@@ -0,0 +1,28 @@
+/*
+ * include/asm-i386/mach-default/mach_segment.h
+ *
+ * user_mode macros moved from include/asm-i386/ptrace.h 08/05
+ */
+
+#ifndef __MACH_SEGMENT_H
+#define __MACH_SEGMENT_H
+
+/*
+ * user_mode_vm(regs) determines whether a register set came from user mode.
+ * This is true if V8086 mode was enabled OR if the register set was from
+ * protected mode with RPL-3 CS value.  This tricky test checks that with
+ * one comparison.  Many places in the kernel can bypass this full check
+ * if they have already ruled out V8086 mode, so user_mode(regs) can be used.
+ */
+static inline int user_mode(struct pt_regs *regs)
+{
+	return (regs->xcs & 3) != 0;
+}
+static inline int user_mode_vm(struct pt_regs *regs)
+{
+	return ((regs->xcs & 3) | (regs->eflags & VM_MASK)) != 0;
+}
+
+#define make_kernel_segment(seg)	(seg)
+
+#endif