x86/signal: Remove pax argument from restore_sigcontext

The 'pax' argument is unnecesary.  Instead, store the RAX value
directly in regs.

This pattern goes all the way back to 2.1.106pre1, when restore_sigcontext()
was changed to return an error code instead of EAX directly:

  https://git.kernel.org/cgit/linux/kernel/git/history/history.git/diff/arch/i386/kernel/signal.c?id=9a8f8b7ca3f319bd668298d447bdf32730e51174

In 2007 sigaltstack syscall support was added, where the return
value of restore_sigcontext() was changed to carry the memory-copying
failure code.

But instead of putting 'ax' into regs->ax directly, it was carried
in via a pointer and then returned, where the generic syscall return
code copied it to regs->ax.

So there was never any deeper reason for this suboptimal pattern, it
was simply never noticed after being introduced.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1428152303-17154-1-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/ia32/ia32_signal.c

@@ -161,8 +161,7 @@ int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
 }
 
 static int ia32_restore_sigcontext(struct pt_regs *regs,
-				   struct sigcontext_ia32 __user *sc,
-				   unsigned int *pax)
+				   struct sigcontext_ia32 __user *sc)
 {
 	unsigned int tmpflags, err = 0;
 	void __user *buf;
@@ -184,7 +183,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
 		RELOAD_SEG(es);
 
 		COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx);
-		COPY(dx); COPY(cx); COPY(ip);
+		COPY(dx); COPY(cx); COPY(ip); COPY(ax);
 		/* Don't touch extended registers */
 
 		COPY_SEG_CPL3(cs);
@@ -197,8 +196,6 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
 
 		get_user_ex(tmp, &sc->fpstate);
 		buf = compat_ptr(tmp);
-
-		get_user_ex(*pax, &sc->ax);
 	} get_user_catch(err);
 
 	err |= restore_xstate_sig(buf, 1);
@@ -213,7 +210,6 @@ asmlinkage long sys32_sigreturn(void)
 	struct pt_regs *regs = current_pt_regs();
 	struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8);
 	sigset_t set;
-	unsigned int ax;
 
 	if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 		goto badframe;
@@ -226,9 +222,9 @@ asmlinkage long sys32_sigreturn(void)
 
 	set_current_blocked(&set);
 
-	if (ia32_restore_sigcontext(regs, &frame->sc, &ax))
+	if (ia32_restore_sigcontext(regs, &frame->sc))
 		goto badframe;
-	return ax;
+	return regs->ax;
 
 badframe:
 	signal_fault(regs, frame, "32bit sigreturn");
@@ -240,7 +236,6 @@ asmlinkage long sys32_rt_sigreturn(void)
 	struct pt_regs *regs = current_pt_regs();
 	struct rt_sigframe_ia32 __user *frame;
 	sigset_t set;
-	unsigned int ax;
 
 	frame = (struct rt_sigframe_ia32 __user *)(regs->sp - 4);
 
@@ -251,13 +246,13 @@ asmlinkage long sys32_rt_sigreturn(void)
 
 	set_current_blocked(&set);
 
-	if (ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
+	if (ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext))
 		goto badframe;
 
 	if (compat_restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	return ax;
+	return regs->ax;
 
 badframe:
 	signal_fault(regs, frame, "32bit rt sigreturn");

arch/x86/include/asm/sighandling.h

@@ -13,9 +13,7 @@
 			 X86_EFLAGS_CF | X86_EFLAGS_RF)
 
 void signal_fault(struct pt_regs *regs, void __user *frame, char *where);
-
-int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
-		       unsigned long *pax);
+int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc);
 int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
 		     struct pt_regs *regs, unsigned long mask);
 

arch/x86/kernel/signal.c

@@ -61,8 +61,7 @@
 	regs->seg = GET_SEG(seg) | 3;			\
 } while (0)
 
-int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
-		       unsigned long *pax)
+int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 {
 	void __user *buf;
 	unsigned int tmpflags;
@@ -81,7 +80,7 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
 #endif /* CONFIG_X86_32 */
 
 		COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx);
-		COPY(dx); COPY(cx); COPY(ip);
+		COPY(dx); COPY(cx); COPY(ip); COPY(ax);
 
 #ifdef CONFIG_X86_64
 		COPY(r8);
@@ -102,8 +101,6 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
 		regs->orig_ax = -1;		/* disable syscall checks */
 
 		get_user_ex(buf, &sc->fpstate);
-
-		get_user_ex(*pax, &sc->ax);
 	} get_user_catch(err);
 
 	err |= restore_xstate_sig(buf, config_enabled(CONFIG_X86_32));
@@ -545,7 +542,6 @@ asmlinkage unsigned long sys_sigreturn(void)
 {
 	struct pt_regs *regs = current_pt_regs();
 	struct sigframe __user *frame;
-	unsigned long ax;
 	sigset_t set;
 
 	frame = (struct sigframe __user *)(regs->sp - 8);
@@ -559,9 +555,9 @@ asmlinkage unsigned long sys_sigreturn(void)
 
 	set_current_blocked(&set);
 
-	if (restore_sigcontext(regs, &frame->sc, &ax))
+	if (restore_sigcontext(regs, &frame->sc))
 		goto badframe;
-	return ax;
+	return regs->ax;
 
 badframe:
 	signal_fault(regs, frame, "sigreturn");
@@ -574,7 +570,6 @@ asmlinkage long sys_rt_sigreturn(void)
 {
 	struct pt_regs *regs = current_pt_regs();
 	struct rt_sigframe __user *frame;
-	unsigned long ax;
 	sigset_t set;
 
 	frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
@@ -585,13 +580,13 @@ asmlinkage long sys_rt_sigreturn(void)
 
 	set_current_blocked(&set);
 
-	if (restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
+	if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
 		goto badframe;
 
 	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	return ax;
+	return regs->ax;
 
 badframe:
 	signal_fault(regs, frame, "rt_sigreturn");
@@ -786,7 +781,6 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
 	struct pt_regs *regs = current_pt_regs();
 	struct rt_sigframe_x32 __user *frame;
 	sigset_t set;
-	unsigned long ax;
 
 	frame = (struct rt_sigframe_x32 __user *)(regs->sp - 8);
 
@@ -797,13 +791,13 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
 
 	set_current_blocked(&set);
 
-	if (restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
+	if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
 		goto badframe;
 
 	if (compat_restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	return ax;
+	return regs->ax;
 
 badframe:
 	signal_fault(regs, frame, "x32 rt_sigreturn");