s390/dis: Fix handling of format specifiers

commit 272fa59c upstream.

The print_insn() function returns strings like "lghi %r1,0". To escape the
'%' character in sprintf() a second '%' is used. For example "lghi %%r1,0"
is converted into "lghi %r1,0".

After print_insn() the output string is passed to printk(). Because format
specifiers like "%r" or "%f" are ignored by printk() this works by chance
most of the time. But for instructions with control registers like
"lctl %c6,%c6,780" this fails because printk() interprets "%c" as
character format specifier.

Fix this problem and escape the '%' characters twice.

For example "lctl %%%%c6,%%%%c6,780" is then converted by sprintf()
into "lctl %%c6,%%c6,780" and by printk() into "lctl %c6,%c6,780".
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[ luis: backported to 3.16:
  - drop condition with OPERAND_VR introduced only with commit
    3585cb02 ("s390/disassembler: add vector instructions") ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

arch/s390/kernel/dis.c

@@ -1726,14 +1726,21 @@ static int print_insn(char *buffer, unsigned char *code, unsigned long addr)
 			}
 			if (separator)
 				ptr += sprintf(ptr, "%c", separator);
+			/*
+			 * Use four '%' characters below because of the
+			 * following two conversions:
+			 *
+			 *  1) sprintf: %%%%r -> %%r
+			 *  2) printk : %%r   -> %r
+			 */
 			if (operand->flags & OPERAND_GPR)
-				ptr += sprintf(ptr, "%%r%i", value);
+				ptr += sprintf(ptr, "%%%%r%i", value);
 			else if (operand->flags & OPERAND_FPR)
-				ptr += sprintf(ptr, "%%f%i", value);
+				ptr += sprintf(ptr, "%%%%f%i", value);
 			else if (operand->flags & OPERAND_AR)
-				ptr += sprintf(ptr, "%%a%i", value);
+				ptr += sprintf(ptr, "%%%%a%i", value);
 			else if (operand->flags & OPERAND_CR)
-				ptr += sprintf(ptr, "%%c%i", value);
+				ptr += sprintf(ptr, "%%%%c%i", value);
 			else if (operand->flags & OPERAND_PCREL)
 				ptr += sprintf(ptr, "%lx", (signed int) value
 								      + addr);