Clean up of patch for letting kernel run other than ring 0:
a. Add some comments about the SEGMENT_IS_*_CODE() macros.
b. Add a USER_RPL macro. (Code was comparing a value to a mask
in some places and to the magic number 3 in other places.)
c. Add macros for table indicator field and use them.
d. Change the entry.S tests for LDT stack segment to use the macros.
Signed-off-by: Chuck Ebbert <[email protected]>
Acked-by: Zachary Amsden <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
diff -r d8064f9b5964 arch/i386/kernel/entry.S
--- a/arch/i386/kernel/entry.S Mon Aug 07 13:30:17 2006 +1000
+++ b/arch/i386/kernel/entry.S Mon Aug 07 14:32:11 2006 +1000
@@ -237,7 +237,7 @@ check_userspace:
movl EFLAGS(%esp), %eax # mix EFLAGS and CS
movb CS(%esp), %al
andl $(VM_MASK | SEGMENT_RPL_MASK), %eax
- cmpl $SEGMENT_RPL_MASK, %eax
+ cmpl $USER_RPL, %eax
jb resume_kernel # not returning to v8086 or userspace
ENTRY(resume_userspace)
DISABLE_INTERRUPTS # make sure we don't miss an interrupt
@@ -374,8 +374,8 @@ restore_all:
# See comments in process.c:copy_thread() for details.
movb OLDSS(%esp), %ah
movb CS(%esp), %al
- andl $(VM_MASK | (4 << 8) | 3), %eax
- cmpl $((4 << 8) | 3), %eax
+ andl $(VM_MASK | (SEGMENT_TI_MASK << 8) | SEGMENT_RPL_MASK), %eax
+ cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax
CFI_REMEMBER_STATE
je ldt_ss # returning to user-space with LDT SS
restore_nocheck:
diff -r d8064f9b5964 include/asm-i386/ptrace.h
--- a/include/asm-i386/ptrace.h Mon Aug 07 13:30:17 2006 +1000
+++ b/include/asm-i386/ptrace.h Mon Aug 07 14:32:11 2006 +1000
@@ -74,11 +74,11 @@ extern void send_sigtrap(struct task_str
*/
static inline int user_mode(struct pt_regs *regs)
{
- return (regs->xcs & SEGMENT_RPL_MASK) == 3;
+ return (regs->xcs & SEGMENT_RPL_MASK) == USER_RPL;
}
static inline int user_mode_vm(struct pt_regs *regs)
{
- return (((regs->xcs & SEGMENT_RPL_MASK) | (regs->eflags & VM_MASK)) >= 3);
+ return ((regs->xcs & SEGMENT_RPL_MASK) | (regs->eflags & VM_MASK)) >= USER_RPL;
}
#define instruction_pointer(regs) ((regs)->eip)
extern unsigned long profile_pc(struct pt_regs *regs);
diff -r d8064f9b5964 include/asm-i386/segment.h
--- a/include/asm-i386/segment.h Mon Aug 07 13:30:17 2006 +1000
+++ b/include/asm-i386/segment.h Mon Aug 07 14:32:11 2006 +1000
@@ -83,10 +83,9 @@
#define GDT_SIZE (GDT_ENTRIES * 8)
-/*
- * Some tricky tests to match code segments after a fault
- */
+/* Matches __KERNEL_CS and __USER_CS (they must be 2 entries apart) */
#define SEGMENT_IS_FLAT_CODE(x) (((x) & 0xec) == GDT_ENTRY_KERNEL_CS * 8)
+/* Matches PNP_CS32 and PNP_CS16 (they must be consecutive) */
#define SEGMENT_IS_PNP_CODE(x) (((x) & 0xf4) == GDT_ENTRY_PNPBIOS_BASE * 8)
/* Simple and small GDT entries for booting only */
@@ -118,8 +117,16 @@
*/
#define IDT_ENTRIES 256
-/* Bottom three bits of xcs give the ring privilege level */
-#define SEGMENT_RPL_MASK 0x3
+/* Bottom two bits of selector give the ring privilege level */
+#define SEGMENT_RPL_MASK 0x3
+/* Bit 2 is table indicator (LDT/GDT) */
+#define SEGMENT_TI_MASK 0x4
+
+/* User mode is privilege level 3 */
+#define USER_RPL 0x3
+/* LDT segment has TI set, GDT has it cleared */
+#define SEGMENT_LDT 0x4
+#define SEGMENT_GDT 0x0
#define get_kernel_rpl() 0
#endif
--
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