From 0998e4228aca046fbd747c3fed909791d52e88eb Mon Sep 17 00:00:00 2001 From: Zachary Amsden Date: Sat, 3 Sep 2005 15:56:43 -0700 Subject: [PATCH] x86: privilege cleanup Privilege checking cleanup. Originally, these diffs were much greater, but recent cleanups in Linux have already done much of the cleanup. I added some explanatory comments in places where the reasoning behind certain tests is rather subtle. Also, in traps.c, we can skip the user_mode check in handle_BUG(). The reason is, there are only two call chains - one via die_if_kernel() and one via do_page_fault(), both entering from die(). Both of these paths already ensure that a kernel mode failure has happened. Also, the original check here, if (user_mode(regs)) was insufficient anyways, since it would not rule out BUG faults from V8086 mode execution. Saving the %ss segment in show_regs() rather than assuming a fixed value also gives better information about the current kernel state in the register dump. Signed-off-by: Zachary Amsden Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/asm-i386/ptrace.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/asm-i386/ptrace.h') diff --git a/include/asm-i386/ptrace.h b/include/asm-i386/ptrace.h index 05532875e39..7e0f2945d17 100644 --- a/include/asm-i386/ptrace.h +++ b/include/asm-i386/ptrace.h @@ -61,6 +61,13 @@ struct pt_regs { 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; -- cgit v1.2.3