[PATCH v4] x86: Avoid pr_cont() in show_opcodes()

From: Tetsuo Handa
Date: Tue Jul 17 2018 - 09:47:11 EST


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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
arch/x86/kernel/dumpstack.c | 25 +++++++------------------
1 file changed, 7 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 666a284..ffdd484 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -93,26 +93,15 @@ 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;
+ const unsigned int prologue = OPCODE_BUFSIZE * 2 / 3;
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, OPCODE_BUFSIZE))
+ printk("%sCode: Bad RIP value.\n", loglvl);
+ else
+ printk("%sCode: %*ph <%02x> %*ph\n", loglvl, prologue, opcodes,
+ opcodes[prologue], OPCODE_BUFSIZE - prologue - 1,
+ &opcodes[prologue + 1]);
}

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