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: Borislav Petkov <bp@suse.de>
Acked-by: Andy 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: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index d20bae2988525292dc1786927c696d93fa218a0a..19507ffa5d28e9ce3ddece3856dd9cde4446f7f8 100644 (file)
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -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

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 56f7e60ad7325bb1a95b2cd38fd8b333c1e16d50..e2888a3ad1e3c3ffd0f2584f34c66f5de0608e19 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -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) &&

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c8eb469a94a46e803ee04c2ea2699859403facff..6751c5c58eecb4d51a67c81e335a3671f994462d 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -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;