[PATCH 10/25] x86/uaccess,signal: Fix AC=1 bloat

From: Peter Zijlstra <peterz@infradead.org>
To: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com,
	julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net,
	mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com,
	valentin.schneider@arm.com, brgerst@gmail.com,
	jpoimboe@redhat.com, luto@kernel.org, bp@alien8.de,
	dvlasenk@redhat.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	dvyukov@google.com, rostedt@goodmis.org
Subject: [PATCH 10/25] x86/uaccess,signal: Fix AC=1 bloat
Date: Mon, 18 Mar 2019 16:38:50 +0100	[thread overview]
Message-ID: <20190318155140.820823912@infradead.org> (raw)
In-Reply-To: 20190318153840.906404905@infradead.org

Occasionally GCC is less agressive with inlining and the following is
observed:

arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x3cc: call to force_valid_ss.isra.5() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x384: call to frame_uc_flags.isra.0() with UACCESS enabled

Cure this by moving this code out of the AC=1 region, since it really
isn't needed for the user access.

Reviewed-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/kernel/signal.c |   29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

--- 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();
@@ -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);
 
@@ -541,6 +543,7 @@ static int x32_setup_rt_frame(struct ksi
 {
 #ifdef CONFIG_X86_X32_ABI
 	struct rt_sigframe_x32 __user *frame;
+	unsigned long uc_flags;
 	void __user *restorer;
 	int err = 0;
 	void __user *fpstate = NULL;
@@ -555,9 +558,11 @@ static int x32_setup_rt_frame(struct ksi
 			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);
 		compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
 		put_user_ex(0, &frame->uc.uc__pad0);


