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Commit 55474c48 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/asm/entry: Remove user_mode_ignore_vm86() 



user_mode_ignore_vm86() can be used instead of user_mode(), in
places where we have already done a v8086_mode() security
check of ptregs.

But doing this check in the wrong place would be a bug that
could result in security problems, and also the naming still
isn't very clear.

Furthermore, it only affects 32-bit kernels, while most
development happens on 64-bit kernels.

If we replace them with user_mode() checks then the cost is only
a very minor increase in various slowpaths:

   text             data   bss     dec              hex    filename
   10573391         703562 1753042 13029995         c6d26b vmlinux.o.before
   10573423         703562 1753042 13030027         c6d28b vmlinux.o.after

So lets get rid of this distinction once and for all.

Acked-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150329090233.GA1963@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a3675b32

arch/x86/include/asm/ptrace.h

+0 −17
Original line number Diff line number Diff line
@@ -113,23 +113,6 @@ static inline int user_mode(struct pt_regs *regs) 
#endif

}



/*

 * This is the fastest way to check whether regs come from user space.

 * It is unsafe if regs might come from vm86 mode, though -- in vm86

 * mode, all bits of CS and SS are completely under the user's control.

 * The CPU considers vm86 mode to be CPL 3 regardless of CS and SS.

 *

 * Do NOT use this function unless you have already ruled out the

 * possibility that regs came from vm86 mode.

 *

 * We check for RPL != 0 instead of RPL == 3 because we don't use rings

 * 1 or 2 and this is more efficient.

 */

static inline int user_mode_ignore_vm86(struct pt_regs *regs)

{

	return (regs->cs & SEGMENT_RPL_MASK) != 0;

}



static inline int v8086_mode(struct pt_regs *regs)

{

#ifdef CONFIG_X86_32

arch/x86/kernel/cpu/perf_event.c

+1 −1
Original line number Diff line number Diff line
@@ -2159,7 +2159,7 @@ static unsigned long code_segment_base(struct pt_regs *regs) 
	if (regs->flags & X86_VM_MASK)

		return 0x10 * regs->cs;



	if (user_mode_ignore_vm86(regs) && regs->cs != __USER_CS)

	if (user_mode(regs) && regs->cs != __USER_CS)

		return get_segment_base(regs->cs);

#else

	if (user_mode(regs) && !user_64bit_mode(regs) &&

arch/x86/kernel/traps.c

+3 −3
Original line number Diff line number Diff line
@@ -207,7 +207,7 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str, 
		return -1;

	}



	if (!user_mode_ignore_vm86(regs)) {

	if (!user_mode(regs)) {

		if (!fixup_exception(regs)) {

			tsk->thread.error_code = error_code;

			tsk->thread.trap_nr = trapnr;
@@ -468,7 +468,7 @@ do_general_protection(struct pt_regs *regs, long error_code) 
	}



	tsk = current;

	if (!user_mode_ignore_vm86(regs)) {

	if (!user_mode(regs)) {

		if (fixup_exception(regs))

			goto exit;
@@ -685,7 +685,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) 
	 * We already checked v86 mode above, so we can check for kernel mode

	 * by just checking the CPL of CS.

	 */

	if ((dr6 & DR_STEP) && !user_mode_ignore_vm86(regs)) {

	if ((dr6 & DR_STEP) && !user_mode(regs)) {

		tsk->thread.debugreg6 &= ~DR_STEP;

		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);

		regs->flags &= ~X86_EFLAGS_TF;