Move x86 signal handler return stub to the vsyscall page,

and stop honoring the SA_RESTORER information.

This will prepare us for alternate signal handler returns.

arch/i386/kernel/signal.c

@@ -378,17 +378,19 @@ static void setup_frame(int sig, struct k_sigaction *ka,
 	if (err)
 		goto give_sigsegv;
 
-	/* Set up to return from userspace.  If provided, use a stub
-	   already in userspace.  */
-	if (ka->sa.sa_flags & SA_RESTORER) {
-		err |= __put_user(ka->sa.sa_restorer, &frame->pretcode);
-	} else {
-		err |= __put_user(frame->retcode, &frame->pretcode);
-		/* This is popl %eax ; movl $,%eax ; int $0x80 */
+	/* Set up to return from userspace.  */
+	err |= __put_user(fix_to_virt(FIX_VSYSCALL) + 32, &frame->pretcode);
+	 
+	/*
+	 * This is popl %eax ; movl $,%eax ; int $0x80
+	 *
+	 * WE DO NOT USE IT ANY MORE! It's only left here for historical
+	 * reasons and because gdb uses it as a signature to notice
+	 * signal handler stack frames.
+	 */
 	err |= __put_user(0xb858, (short *)(frame->retcode+0));
 	err |= __put_user(__NR_sigreturn, (int *)(frame->retcode+2));
 	err |= __put_user(0x80cd, (short *)(frame->retcode+6));
-	}
 
 	if (err)
 		goto give_sigsegv;
@@ -453,17 +455,19 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 	if (err)
 		goto give_sigsegv;
 
-	/* Set up to return from userspace.  If provided, use a stub
-	   already in userspace.  */
-	if (ka->sa.sa_flags & SA_RESTORER) {
-		err |= __put_user(ka->sa.sa_restorer, &frame->pretcode);
-	} else {
-		err |= __put_user(frame->retcode, &frame->pretcode);
-		/* This is movl $,%eax ; int $0x80 */
+	/* Set up to return from userspace.  */
+	err |= __put_user(fix_to_virt(FIX_VSYSCALL) + 64, &frame->pretcode);
+	 
+	/*
+	 * This is movl $,%eax ; int $0x80
+	 *
+	 * WE DO NOT USE IT ANY MORE! It's only left here for historical
+	 * reasons and because gdb uses it as a signature to notice
+	 * signal handler stack frames.
+	 */
 	err |= __put_user(0xb8, (char *)(frame->retcode+0));
 	err |= __put_user(__NR_rt_sigreturn, (int *)(frame->retcode+1));
 	err |= __put_user(0x80cd, (short *)(frame->retcode+5));
-	}
 
 	if (err)
 		goto give_sigsegv;

arch/i386/kernel/sysenter.c

@@ -16,6 +16,7 @@
 #include <asm/cpufeature.h>
 #include <asm/msr.h>
 #include <asm/pgtable.h>
+#include <asm/unistd.h>
 
 extern asmlinkage void sysenter_entry(void);
 
@@ -73,10 +74,23 @@ static int __init sysenter_setup(void)
 		0x59,			/* pop %ecx */
 		0xc3			/* ret */
 	};
+	static const char sigreturn[] = {
+	/* 32: sigreturn point */
+		0x58,				/* popl %eax */
+		0xb8, __NR_sigreturn, 0, 0, 0,	/* movl $__NR_sigreturn, %eax */
+		0xcd, 0x80,			/* int $0x80 */
+	};
+	static const char rt_sigreturn[] = {
+	/* 64: rt_sigreturn point */
+		0xb8, __NR_rt_sigreturn, 0, 0, 0,	/* movl $__NR_rt_sigreturn, %eax */
+		0xcd, 0x80,			/* int $0x80 */
+	};
 	unsigned long page = get_zeroed_page(GFP_ATOMIC);
 
 	__set_fixmap(FIX_VSYSCALL, __pa(page), PAGE_READONLY);
 	memcpy((void *) page, int80, sizeof(int80));
+	memcpy((void *)(page + 32), sigreturn, sizeof(sigreturn));
+	memcpy((void *)(page + 64), rt_sigreturn, sizeof(rt_sigreturn));
 	if (!boot_cpu_has(X86_FEATURE_SEP))
 		return 0;