Patch "MIPS: Prevent unaligned accesses during stack unwinding" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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

    MIPS: Prevent unaligned accesses during stack unwinding

to the 4.9-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:
     mips-prevent-unaligned-accesses-during-stack-unwinding.patch
and it can be found in the queue-4.9 subdirectory.

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


>From a3552dace7d1d0cabf573e88fc3025cb90c4a601 Mon Sep 17 00:00:00 2001
From: Paul Burton <paul.burton@imgtec.com>
Date: Mon, 7 Nov 2016 15:07:03 +0000
Subject: MIPS: Prevent unaligned accesses during stack unwinding

From: Paul Burton <paul.burton@imgtec.com>

commit a3552dace7d1d0cabf573e88fc3025cb90c4a601 upstream.

During stack unwinding we call a number of functions to determine what
type of instruction we're looking at. The union mips_instruction pointer
provided to them may be pointing at a 2 byte, but not 4 byte, aligned
address & we thus cannot directly access the 4 byte wide members of the
union mips_instruction. To avoid this is_ra_save_ins() copies the
required half-words of the microMIPS instruction to a correctly aligned
union mips_instruction on the stack, which it can then access safely.
The is_jump_ins() & is_sp_move_ins() functions do not correctly perform
this temporary copy, and instead attempt to directly dereference 4 byte
fields which may be misaligned and lead to an address exception.

Fix this by copying the instruction halfwords to a temporary union
mips_instruction in get_frame_info() such that we can provide a 4 byte
aligned union mips_instruction to the is_*_ins() functions and they do
not need to deal with misalignment themselves.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: 34c2f668d0f6 ("MIPS: microMIPS: Add unaligned access support.")
Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14529/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/kernel/process.c |   70 ++++++++++++++++++++++-----------------------
 1 file changed, 35 insertions(+), 35 deletions(-)

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -198,8 +198,6 @@ struct mips_frame_info {
 static inline int is_ra_save_ins(union mips_instruction *ip)
 {
 #ifdef CONFIG_CPU_MICROMIPS
-	union mips_instruction mmi;
-
 	/*
 	 * swsp ra,offset
 	 * swm16 reglist,offset(sp)
@@ -209,23 +207,20 @@ static inline int is_ra_save_ins(union m
 	 *
 	 * microMIPS is way more fun...
 	 */
-	if (mm_insn_16bit(ip->halfword[0])) {
-		mmi.word = (ip->halfword[0] << 16);
-		return (mmi.mm16_r5_format.opcode == mm_swsp16_op &&
-			mmi.mm16_r5_format.rt == 31) ||
-		       (mmi.mm16_m_format.opcode == mm_pool16c_op &&
-			mmi.mm16_m_format.func == mm_swm16_op);
+	if (mm_insn_16bit(ip->halfword[1])) {
+		return (ip->mm16_r5_format.opcode == mm_swsp16_op &&
+			ip->mm16_r5_format.rt == 31) ||
+		       (ip->mm16_m_format.opcode == mm_pool16c_op &&
+			ip->mm16_m_format.func == mm_swm16_op);
 	}
 	else {
-		mmi.halfword[0] = ip->halfword[1];
-		mmi.halfword[1] = ip->halfword[0];
-		return (mmi.mm_m_format.opcode == mm_pool32b_op &&
-			mmi.mm_m_format.rd > 9 &&
-			mmi.mm_m_format.base == 29 &&
-			mmi.mm_m_format.func == mm_swm32_func) ||
-		       (mmi.i_format.opcode == mm_sw32_op &&
-			mmi.i_format.rs == 29 &&
-			mmi.i_format.rt == 31);
+		return (ip->mm_m_format.opcode == mm_pool32b_op &&
+			ip->mm_m_format.rd > 9 &&
+			ip->mm_m_format.base == 29 &&
+			ip->mm_m_format.func == mm_swm32_func) ||
+		       (ip->i_format.opcode == mm_sw32_op &&
+			ip->i_format.rs == 29 &&
+			ip->i_format.rt == 31);
 	}
 #else
 	/* sw / sd $ra, offset($sp) */
@@ -246,12 +241,8 @@ static inline int is_jump_ins(union mips
 	 *
 	 * microMIPS is kind of more fun...
 	 */
-	union mips_instruction mmi;
-
-	mmi.word = (ip->halfword[0] << 16);
-
-	if ((mmi.mm16_r5_format.opcode == mm_pool16c_op &&
-	    (mmi.mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op) ||
+	if ((ip->mm16_r5_format.opcode == mm_pool16c_op &&
+	    (ip->mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op) ||
 	    ip->j_format.opcode == mm_jal32_op)
 		return 1;
 	if (ip->r_format.opcode != mm_pool32a_op ||
@@ -280,15 +271,13 @@ static inline int is_sp_move_ins(union m
 	 *
 	 * microMIPS is not more fun...
 	 */
-	if (mm_insn_16bit(ip->halfword[0])) {
-		union mips_instruction mmi;
-
-		mmi.word = (ip->halfword[0] << 16);
-		return (mmi.mm16_r3_format.opcode == mm_pool16d_op &&
-			mmi.mm16_r3_format.simmediate && mm_addiusp_func) ||
-		       (mmi.mm16_r5_format.opcode == mm_pool16d_op &&
-			mmi.mm16_r5_format.rt == 29);
+	if (mm_insn_16bit(ip->halfword[1])) {
+		return (ip->mm16_r3_format.opcode == mm_pool16d_op &&
+			ip->mm16_r3_format.simmediate && mm_addiusp_func) ||
+		       (ip->mm16_r5_format.opcode == mm_pool16d_op &&
+			ip->mm16_r5_format.rt == 29);
 	}
+
 	return ip->mm_i_format.opcode == mm_addiu32_op &&
 	       ip->mm_i_format.rt == 29 && ip->mm_i_format.rs == 29;
 #else
@@ -303,7 +292,8 @@ static inline int is_sp_move_ins(union m
 
 static int get_frame_info(struct mips_frame_info *info)
 {
-	union mips_instruction *ip;
+	bool is_mmips = IS_ENABLED(CONFIG_CPU_MICROMIPS);
+	union mips_instruction insn, *ip;
 	unsigned max_insns = info->func_size / sizeof(union mips_instruction);
 	unsigned i;
 
@@ -319,11 +309,21 @@ static int get_frame_info(struct mips_fr
 	max_insns = min(128U, max_insns);
 
 	for (i = 0; i < max_insns; i++, ip++) {
+		if (is_mmips && mm_insn_16bit(ip->halfword[0])) {
+			insn.halfword[0] = 0;
+			insn.halfword[1] = ip->halfword[0];
+		} else if (is_mmips) {
+			insn.halfword[0] = ip->halfword[1];
+			insn.halfword[1] = ip->halfword[0];
+		} else {
+			insn.word = ip->word;
+		}
 
-		if (is_jump_ins(ip))
+		if (is_jump_ins(&insn))
 			break;
+
 		if (!info->frame_size) {
-			if (is_sp_move_ins(ip))
+			if (is_sp_move_ins(&insn))
 			{
 #ifdef CONFIG_CPU_MICROMIPS
 				if (mm_insn_16bit(ip->halfword[0]))
@@ -346,7 +346,7 @@ static int get_frame_info(struct mips_fr
 			}
 			continue;
 		}
-		if (info->pc_offset == -1 && is_ra_save_ins(ip)) {
+		if (info->pc_offset == -1 && is_ra_save_ins(&insn)) {
 			info->pc_offset =
 				ip->i_format.simmediate / sizeof(long);
 			break;


Patches currently in stable-queue which might be from paul.burton@imgtec.com are

queue-4.9/mips-calculate-micromips-ra-properly-when-unwinding-the-stack.patch
queue-4.9/mips-fix-get_frame_info-handling-of-micromips-function-size.patch
queue-4.9/mips-handle-micromips-jumps-in-the-same-way-as-mips32-mips64-jumps.patch
queue-4.9/mips-fix-is_jump_ins-handling-of-16b-micromips-instructions.patch
queue-4.9/mips-clear-isa-bit-correctly-in-get_frame_info.patch
queue-4.9/mips-prevent-unaligned-accesses-during-stack-unwinding.patch