[PATCH] i386: Allow a kernel not to be in ring 0
We allow for the fact that the guest kernel may not run in ring 0. This
requires some abstraction in a few places when setting %cs or checking
privilege level (user vs kernel).
This is Chris' [RFC PATCH 15/33] move segment checks to subarch, except rather
than using #define USER_MODE_MASK which depends on a config option, we use
Zach's more flexible approach of assuming ring 3 == userspace. I also used
"get_kernel_rpl()" over "get_kernel_cs()" because I think it reads better in
the code...
1) Remove the hardcoded 3 and introduce #define SEGMENT_RPL_MASK 3 2) Add a
get_kernel_rpl() macro, and don't assume it's zero.
And:
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: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>
diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 3872fca..284f2e9 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -240,8 +240,9 @@
check_userspace:
movl EFLAGS(%esp), %eax # mix EFLAGS and CS
movb CS(%esp), %al
- testl $(VM_MASK | 3), %eax
- jz resume_kernel
+ andl $(VM_MASK | 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
# setting need_resched or sigpending
@@ -377,8 +378,8 @@
# 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: