linux-kernel - [PATCH 4.2.y-ckt 231/305] s390/dis: Fix handling of format specifiers

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Date:	Fri, 15 Jan 2016 16:00:45 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 231/305] s390/dis: Fix handling of format specifiers

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Michael Holzheu <holzheu@...ux.vnet.ibm.com>

commit 272fa59ccb4fc802af28b1d699c2463db6a71bf7 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@...ux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/s390/kernel/dis.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kernel/dis.c b/arch/s390/kernel/dis.c
index 8140d10..6e72961 100644
--- a/arch/s390/kernel/dis.c
+++ b/arch/s390/kernel/dis.c
@@ -1920,16 +1920,23 @@ 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_VR)
-				ptr += sprintf(ptr, "%%v%i", value);
+				ptr += sprintf(ptr, "%%%%v%i", value);
 			else if (operand->flags & OPERAND_PCREL)
 				ptr += sprintf(ptr, "%lx", (signed int) value
 								      + addr);
-- 
1.9.1