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. Signed-off-by: Rusty Russell Signed-off-by: Zachary Amsden Signed-off-by: Jeremy Fitzhardinge --- arch/i386/kernel/entry.S | 5 +++-- arch/i386/kernel/process.c | 2 +- arch/i386/mm/extable.c | 2 +- arch/i386/mm/fault.c | 11 ++++------- include/asm-i386/ptrace.h | 5 +++-- include/asm-i386/segment.h | 10 ++++++++++ 6 files changed, 22 insertions(+), 13 deletions(-) =================================================================== --- a/arch/i386/kernel/entry.S +++ b/arch/i386/kernel/entry.S @@ -229,8 +229,9 @@ check_userspace: 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 $SEGMENT_RPL_MASK, %eax + jb resume_kernel # not returning to v8086 or userspace ENTRY(resume_userspace) cli # make sure we don't miss an interrupt # setting need_resched or sigpending =================================================================== --- a/arch/i386/kernel/process.c +++ b/arch/i386/kernel/process.c @@ -346,7 +346,7 @@ int kernel_thread(int (*fn)(void *), voi regs.xes = __USER_DS; regs.orig_eax = -1; regs.eip = (unsigned long) kernel_thread_helper; - regs.xcs = __KERNEL_CS; + regs.xcs = __KERNEL_CS | get_kernel_rpl(); regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2; /* Ok, create the new process.. */ =================================================================== --- a/arch/i386/mm/extable.c +++ b/arch/i386/mm/extable.c @@ -11,7 +11,7 @@ int fixup_exception(struct pt_regs *regs const struct exception_table_entry *fixup; #ifdef CONFIG_PNPBIOS - if (unlikely((regs->xcs & ~15) == (GDT_ENTRY_PNPBIOS_BASE << 3))) + if (unlikely(SEGMENT_IS_PNP_CODE(regs->xcs))) { extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp; extern u32 pnp_bios_is_utter_crap; =================================================================== --- a/arch/i386/mm/fault.c +++ b/arch/i386/mm/fault.c @@ -27,6 +27,7 @@ #include #include #include +#include extern void die(const char *,struct pt_regs *,long); @@ -119,10 +120,10 @@ static inline unsigned long get_segment_ } /* The standard kernel/user address space limit. */ - *eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg; + *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg; /* By far the most common cases. */ - if (likely(seg == __USER_CS || seg == __KERNEL_CS)) + if (likely(SEGMENT_IS_FLAT_CODE(seg))) return eip; /* Check the segment exists, is within the current LDT/GDT size, @@ -436,11 +437,7 @@ good_area: write = 0; switch (error_code & 3) { default: /* 3: write, present */ -#ifdef TEST_VERIFY_AREA - if (regs->cs == KERNEL_CS) - printk("WP fault at %08lx\n", regs->eip); -#endif - /* fall through */ + /* fall through */ case 2: /* write, not present */ if (!(vma->vm_flags & VM_WRITE)) goto bad_area; =================================================================== --- a/include/asm-i386/ptrace.h +++ b/include/asm-i386/ptrace.h @@ -60,6 +60,7 @@ struct pt_regs { #ifdef __KERNEL__ #include +#include 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_str */ static inline int user_mode(struct pt_regs *regs) { - return (regs->xcs & 3) != 0; + return (regs->xcs & SEGMENT_RPL_MASK) == 3; } 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)) >= 3); } #define instruction_pointer(regs) ((regs)->eip) #if defined(CONFIG_SMP) && defined(CONFIG_FRAME_POINTER) =================================================================== --- a/include/asm-i386/segment.h +++ b/include/asm-i386/segment.h @@ -83,6 +83,12 @@ #define GDT_SIZE (GDT_ENTRIES * 8) +/* + * Some tricky tests to match code segments after a fault + */ +#define SEGMENT_IS_FLAT_CODE(x) (((x) & 0xec) == GDT_ENTRY_KERNEL_CS * 8) +#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 +118,8 @@ */ #define IDT_ENTRIES 256 +/* Bottom three bits of xcs give the ring privilege level */ +#define SEGMENT_RPL_MASK 0x3 + +#define get_kernel_rpl() 0 #endif -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/