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[PATCH] i386: Allow a kernel not to be in ring 0

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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 <[email protected]>
Signed-off-by: Zachary Amsden <[email protected]>
Signed-off-by: Jeremy Fitzhardinge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
This commit is contained in:
Rusty Russell 2006-09-26 10:52:39 +02:00 • committed by Andi Kleen
commit 78be3706b2
6 changed files with 31 additions and 15 deletions
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5
include/asm-i386/ptrace.h
View file

@ -60,6 +60,7 @@ struct pt_regs {
#ifdef __KERNEL__
#include <asm/vm86.h>
#include <asm/segment.h>
struct task_struct;
extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);
@ -73,11 +74,11 @@ extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int erro
*/
static inline int user_mode(struct pt_regs *regs)
{
return (regs->xcs & 3) != 0;
return (regs->xcs & SEGMENT_RPL_MASK) == USER_RPL;
}
static inline int user_mode_vm(struct pt_regs *regs)
{
return ((regs->xcs & 3) | (regs->eflags & VM_MASK)) != 0;
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);

17
include/asm-i386/segment.h
View file

@ -83,6 +83,11 @@
#define GDT_SIZE (GDT_ENTRIES * 8)
/* 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 */
#define GDT_ENTRY_BOOT_CS 2
@ -112,4 +117,16 @@
*/
#define IDT_ENTRIES 256
/* 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