Patch "ARM: 8720/1: ensure dump_instr() checks addr_limit" has been added to the 4.13-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ARM: 8720/1: ensure dump_instr() checks addr_limit

to the 4.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm-8720-1-ensure-dump_instr-checks-addr_limit.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From b9dd05c7002ee0ca8b676428b2268c26399b5e31 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Thu, 2 Nov 2017 18:44:28 +0100
Subject: ARM: 8720/1: ensure dump_instr() checks addr_limit

From: Mark Rutland <mark.rutland@xxxxxxx>

commit b9dd05c7002ee0ca8b676428b2268c26399b5e31 upstream.

When CONFIG_DEBUG_USER is enabled, it's possible for a user to
deliberately trigger dump_instr() with a chosen kernel address.

Let's avoid problems resulting from this by using get_user() rather than
__get_user(), ensuring that we don't erroneously access kernel memory.

So that we can use the same code to dump user instructions and kernel
instructions, the common dumping code is factored out to __dump_instr(),
with the fs manipulated appropriately in dump_instr() around calls to
this.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm/kernel/traps.c |   28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -154,30 +154,26 @@ static void dump_mem(const char *lvl, co
 	set_fs(fs);
 }
 
-static void dump_instr(const char *lvl, struct pt_regs *regs)
+static void __dump_instr(const char *lvl, struct pt_regs *regs)
 {
 	unsigned long addr = instruction_pointer(regs);
 	const int thumb = thumb_mode(regs);
 	const int width = thumb ? 4 : 8;
-	mm_segment_t fs;
 	char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
 	int i;
 
 	/*
-	 * We need to switch to kernel mode so that we can use __get_user
-	 * to safely read from kernel space.  Note that we now dump the
-	 * code first, just in case the backtrace kills us.
+	 * Note that we now dump the code first, just in case the backtrace
+	 * kills us.
 	 */
-	fs = get_fs();
-	set_fs(KERNEL_DS);
 
 	for (i = -4; i < 1 + !!thumb; i++) {
 		unsigned int val, bad;
 
 		if (thumb)
-			bad = __get_user(val, &((u16 *)addr)[i]);
+			bad = get_user(val, &((u16 *)addr)[i]);
 		else
-			bad = __get_user(val, &((u32 *)addr)[i]);
+			bad = get_user(val, &((u32 *)addr)[i]);
 
 		if (!bad)
 			p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ",
@@ -188,8 +184,20 @@ static void dump_instr(const char *lvl,
 		}
 	}
 	printk("%sCode: %s\n", lvl, str);
+}
 
-	set_fs(fs);
+static void dump_instr(const char *lvl, struct pt_regs *regs)
+{
+	mm_segment_t fs;
+
+	if (!user_mode(regs)) {
+		fs = get_fs();
+		set_fs(KERNEL_DS);
+		__dump_instr(lvl, regs);
+		set_fs(fs);
+	} else {
+		__dump_instr(lvl, regs);
+	}
 }
 
 #ifdef CONFIG_ARM_UNWIND


Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are

queue-4.13/arm-8720-1-ensure-dump_instr-checks-addr_limit.patch