Patch "MIPS: Fix get_frame_info() handling of microMIPS function size" has been added to the 4.4-stable tree

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

MIPS: Fix get_frame_info() handling of microMIPS function size

to the 4.4-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-fix-get_frame_info-handling-of-micromips-function-size.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Burton <[email protected]>
Date: Mon, 7 Nov 2016 15:07:04 +0000
Subject: MIPS: Fix get_frame_info() handling of microMIPS function size

From: Paul Burton <[email protected]>

commit b6c7a324df37bf05ef7a2c1580683cf10d082d97 upstream.

get_frame_info() is meant to iterate over up to the first 128 instructions within a function, but for microMIPS kernels it will not reach that many instructions unless the function is 512 bytes long since we calculate the maximum number of instructions to check by dividing the function length by the 4 byte size of a union mips_instruction. In microMIPS kernels this won't do since instructions are variable length.

Fix this by instead checking whether the pointer to the current instruction has reached the end of the function, and use max_insns as a simple constant to check the number of iterations against.

Patchwork: https://patchwork.linux-mips.org/patch/14530/

---
 arch/mips/kernel/process.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

@@ -289,9 +289,9 @@ static inline int is_sp_move_ins(union m
 static int get_frame_info(struct mips_frame_info *info)
 {
 	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;
+	union mips_instruction insn, *ip, *ip_end;
+	const unsigned int max_insns = 128;
+	unsigned int i;
 
 	info->pc_offset = -1;
 	info->frame_size = 0;

@@ -300,11 +300,9 @@ static int get_frame_info(struct mips_fr
 	if (!ip)
 		goto err;
 
-	if (max_insns == 0)
-		max_insns = 128U;	/* unknown function size */
-	max_insns = min(128U, max_insns);
+	ip_end = (void *)ip + info->func_size;
 
-	for (i = 0; i < max_insns; i++, ip++) {
+	for (i = 0; i < max_insns && ip < ip_end; i++, ip++) {
 		if (is_mmips && mm_insn_16bit(ip->halfword[0])) {
 			insn.halfword[0] = 0;
 			insn.halfword[1] = ip->halfword[0];

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mips-calculate-micromips-ra-properly-when-unwinding-the-stack.patch queue-4.4/mips-fix-get_frame_info-handling-of-micromips-function-size.patch queue-4.4/mips-handle-micromips-jumps-in-the-same-way-as-mips32-mips64-jumps.patch queue-4.4/mips-fix-is_jump_ins-handling-of-16b-micromips-instructions.patch queue-4.4/mips-clear-isa-bit-correctly-in-get_frame_info.patch queue-4.4/mips-prevent-unaligned-accesses-during-stack-unwinding.patch