linux-kernel - [PATCH 2/3] MN10300: die_if_no_fixup() shouldn't use get_user() as it doesn't call set

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Date:	Mon, 06 Jun 2011 15:47:14 +0100
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...l.org, akpm@...ux-foundation.org
Cc:	linux-am33-list@...hat.com, linux-kernel@...r.kernel.org,
	David Howells <dhowells@...hat.com>
Subject: [PATCH 2/3] MN10300: die_if_no_fixup() shouldn't use get_user() as it
 doesn't call set_fs()

die_if_no_fixup() shouldn't use get_user() as it doesn't call set_fs() to
indicate that it wants to probe a kernel address.  Instead it should use
probe_kernel_read().

This fixes the problem of gdb seeing SIGILL rather than SIGTRAP when hitting
the KGDB special breakpoint upon SysRq+g being seen.  The problem was that
die_if_no_fixup() was failing to read the opcode of the instruction that caused
the exception, and thus not fixing up the exception.

This caused gdb to get a S04 response to the $? request in its remote protocol
rather than S05 - which would then cause it to continue with $C04 rather than
$c in an attempt to pass the signal onto the inferior process.  The kernel,
however, does not support $Cnn, and so objects by returning an E22 response,
indicating an error.  gdb does not expect this and prints:

	warning: Remote failure reply: E22

and then returns to the gdb command prompt unable to continue.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 arch/mn10300/kernel/traps.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mn10300/kernel/traps.c b/arch/mn10300/kernel/traps.c
index f03cb27..bd3e5e7 100644
--- a/arch/mn10300/kernel/traps.c
+++ b/arch/mn10300/kernel/traps.c
@@ -28,7 +28,7 @@
 #include <linux/irq.h>
 #include <asm/processor.h>
 #include <asm/system.h>
-#include <asm/uaccess.h>
+#include <linux/uaccess.h>
 #include <asm/io.h>
 #include <asm/atomic.h>
 #include <asm/smp.h>
@@ -156,7 +156,7 @@ int die_if_no_fixup(const char *str, struct pt_regs *regs,

 	case EXCEP_TRAP:
 	case EXCEP_UNIMPINS:
-		if (get_user(opcode, (uint8_t __user *)regs->pc) != 0)
+		if (probe_kernel_read(&opcode, (u8 *)regs->pc, 1) < 0)
 			break;
 		if (opcode == 0xff) {
 			if (notify_die(DIE_BREAKPOINT, str, regs, code, 0, 0))

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