sparc64: Make corrupted user stacks more debuggable.

Right now if we get a corrupted user stack frame we do a
do_exit(SIGILL) which is not helpful.

If under a debugger, this behavior causes the inferior process to
exit. So the register and other state cannot be examined at the time
of the event.

Instead, conditionally log a rate limited kernel log message and then
force a SIGSEGV.

With bits and ideas borrowed (as usual) from powerpc.

Signed-off-by: David S. Miller <[e-mail]>

arch/sparc/include/asm/switch_to_64.h

···
 } while(0)
 
 void synchronize_user_stack(void);
-void fault_in_user_windows(void);
+struct pt_regs;
+void fault_in_user_windows(struct pt_regs *);
 
 #endif /* __SPARC64_SWITCH_TO_64_H */

arch/sparc/kernel/process_64.c

···
 #include <linux/sysrq.h>
 #include <linux/nmi.h>
 #include <linux/context_tracking.h>
+#include <linux/signal.h>
 
 #include <linux/uaccess.h>
 #include <asm/page.h>
···
 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *) sp, 0, current);
 }
 
-void fault_in_user_windows(void)
+static const char uwfault32[] = KERN_INFO \
+	"%s[%d]: bad register window fault: SP %08lx (orig_sp %08lx) TPC %08lx O7 %08lx\n";
+static const char uwfault64[] = KERN_INFO \
+	"%s[%d]: bad register window fault: SP %016lx (orig_sp %016lx) TPC %08lx O7 %016lx\n";
+
+void fault_in_user_windows(struct pt_regs *regs)
 {
 	struct thread_info *t = current_thread_info();
 	unsigned long window;
···
 		do {
 			struct reg_window *rwin = &t->reg_window[window];
 			int winsize = sizeof(struct reg_window);
-			unsigned long sp;
+			unsigned long sp, orig_sp;
 
-			sp = t->rwbuf_stkptrs[window];
+			orig_sp = sp = t->rwbuf_stkptrs[window];
 
 			if (test_thread_64bit_stack(sp))
 				sp += STACK_BIAS;
···
 				stack_unaligned(sp);
 
 			if (unlikely(copy_to_user((char __user *)sp,
-						  rwin, winsize)))
+						  rwin, winsize))) {
+				if (show_unhandled_signals)
+					printk_ratelimited(is_compat_task() ?
+							   uwfault32 : uwfault64,
+							   current->comm, current->pid,
+							   sp, orig_sp,
+							   regs->tpc,
+							   regs->u_regs[UREG_I7]);
 				goto barf;
+			}
 		} while (window--);
 	}
 	set_thread_wsaved(0);
···
 
 barf:
 	set_thread_wsaved(window + 1);
-	user_exit();
-	do_exit(SIGILL);
+	force_sig(SIGSEGV, current);
 }
 
 asmlinkage long sparc_do_fork(unsigned long clone_flags,

arch/sparc/kernel/rtrap_64.S

···
 		 wrpr			%g0, RTRAP_PSTATE_IRQOFF, %pstate
 
 __handle_user_windows:
+		add			%sp, PTREGS_OFF, %o0
 		call			fault_in_user_windows
 661:		 wrpr			%g0, RTRAP_PSTATE, %pstate
 		/* If userspace is using ADI, it could potentially pass

arch/sparc/kernel/signal32.c

···
 		get_sigframe(ksig, regs, sigframe_size);
 	
 	if (invalid_frame_pointer(sf, sigframe_size)) {
-		do_exit(SIGILL);
+		if (show_unhandled_signals)
+			pr_info("%s[%d] bad frame in setup_frame32: %08lx TPC %08lx O7 %08lx\n",
+				current->comm, current->pid, (unsigned long)sf,
+				regs->tpc, regs->u_regs[UREG_I7]);
+		force_sigsegv(ksig->sig, current);
 		return -EINVAL;
 	}
 
···
 		get_sigframe(ksig, regs, sigframe_size);
 	
 	if (invalid_frame_pointer(sf, sigframe_size)) {
-		do_exit(SIGILL);
+		if (show_unhandled_signals)
+			pr_info("%s[%d] bad frame in setup_rt_frame32: %08lx TPC %08lx O7 %08lx\n",
+				current->comm, current->pid, (unsigned long)sf,
+				regs->tpc, regs->u_regs[UREG_I7]);
+		force_sigsegv(ksig->sig, current);
 		return -EINVAL;
 	}
 

arch/sparc/kernel/signal_64.c

···
 		get_sigframe(ksig, regs, sf_size);
 
 	if (invalid_frame_pointer (sf)) {
-		do_exit(SIGILL);	/* won't return, actually */
+		if (show_unhandled_signals)
+			pr_info("%s[%d] bad frame in setup_rt_frame: %016lx TPC %016lx O7 %016lx\n",
+				current->comm, current->pid, (unsigned long)sf,
+				regs->tpc, regs->u_regs[UREG_I7]);
+		force_sigsegv(ksig->sig, current);
 		return -EINVAL;
 	}