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Subject[PATCH v5] x86: Avoid pr_cont() in show_opcodes().
Date
Since syzbot is confused by concurrent printk() messages [1],
this patch changes show_opcodes() to use %ph format string.

When we start adding prefix to each line of printk() output,
we will be able to handle concurrent printk() messages.

[1] https://syzkaller.appspot.com/text?tag=CrashReport&x=139d342c400000

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Borislav Petkov <bp@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
---
arch/x86/kernel/dumpstack.c | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 666a284..0821da3 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -22,8 +22,6 @@
#include <asm/stacktrace.h>
#include <asm/unwind.h>

-#define OPCODE_BUFSIZE 64
-
int panic_on_unrecovered_nmi;
int panic_on_io_nmi;
static int die_counter;
@@ -93,26 +91,17 @@ static void printk_stack_address(unsigned long address, int reliable,
*/
void show_opcodes(u8 *rip, const char *loglvl)
{
- unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
+#define PROLOGUE_SIZE 42
+#define EPILOGUE_SIZE 21
+#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE];
- u8 *ip;
- int i;
-
- printk("%sCode: ", loglvl);

- ip = (u8 *)rip - code_prologue;
- if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
- pr_cont("Bad RIP value.\n");
- return;
- }
-
- for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) {
- if (ip == rip)
- pr_cont("<%02x> ", opcodes[i]);
- else
- pr_cont("%02x ", opcodes[i]);
- }
- pr_cont("\n");
+ if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE))
+ printk("%sCode: Bad RIP value.\n", loglvl);
+ else
+ printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
+ __stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes,
+ opcodes[PROLOGUE_SIZE], opcodes + PROLOGUE_SIZE + 1);
}

void show_ip(struct pt_regs *regs, const char *loglvl)
--
1.8.3.1
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