Re: [PATCH 07/20] x86/uaccess: Always inline force_valid_ss()

[Peter Zijlstra]

On Thu, Mar 07, 2019 at 10:05:43AM -0800, Andy Lutomirski wrote:
> On Thu, Mar 7, 2019 at 3:52 AM Peter Zijlstra <pet...@infradead.org> wrote:
> >
> > arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x3cc: 
> > call to force_valid_ss.isra.5() with UACCESS enabled
> >
> > XXX: move the callsite out of te AC=1 region instead?
> 
> Let's move it instead.  I looked at the code and it should be fine.

Something like so; or did I miss something subtle?

--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -132,16 +132,6 @@ static int restore_sigcontext(struct pt_
                COPY_SEG_CPL3(cs);
                COPY_SEG_CPL3(ss);
 
-#ifdef CONFIG_X86_64
-               /*
-                * Fix up SS if needed for the benefit of old DOSEMU and
-                * CRIU.
-                */
-               if (unlikely(!(uc_flags & UC_STRICT_RESTORE_SS) &&
-                            user_64bit_mode(regs)))
-                       force_valid_ss(regs);
-#endif
-
                get_user_ex(tmpflags, &sc->flags);
                regs->flags = (regs->flags & ~FIX_EFLAGS) | (tmpflags & 
FIX_EFLAGS);
                regs->orig_ax = -1;             /* disable syscall checks */
@@ -150,6 +140,15 @@ static int restore_sigcontext(struct pt_
                buf = (void __user *)buf_val;
        } get_user_catch(err);
 
+#ifdef CONFIG_X86_64
+       /*
+        * Fix up SS if needed for the benefit of old DOSEMU and
+        * CRIU.
+        */
+       if (unlikely(!(uc_flags & UC_STRICT_RESTORE_SS) && 
user_64bit_mode(regs)))
+               force_valid_ss(regs);
+#endif
+
        err |= fpu__restore_sig(buf, IS_ENABLED(CONFIG_X86_32));
 
        force_iret();
@@ -441,7 +440,7 @@ static int __setup_rt_frame(int sig, str
        return 0;
 }
 #else /* !CONFIG_X86_32 */
-static unsigned long frame_uc_flags(struct pt_regs *regs)
+static __always_inline unsigned long frame_uc_flags(struct pt_regs *regs)
 {
        unsigned long flags;
 
@@ -461,6 +460,7 @@ static int __setup_rt_frame(int sig, str
 {
        struct rt_sigframe __user *frame;
        void __user *fp = NULL;
+       unsigned long uc_flags;
        int err = 0;
 
        frame = get_sigframe(&ksig->ka, regs, sizeof(struct rt_sigframe), &fp);
@@ -473,9 +473,11 @@ static int __setup_rt_frame(int sig, str
                        return -EFAULT;
        }
 
+       uc_flags = frame_uc_flags(regs);
+
        put_user_try {
                /* Create the ucontext.  */
-               put_user_ex(frame_uc_flags(regs), &frame->uc.uc_flags);
+               put_user_ex(uc_flags, &frame->uc.uc_flags);
                put_user_ex(0, &frame->uc.uc_link);
                save_altstack_ex(&frame->uc.uc_stack, regs->sp);