[PATCH v2] ARC: prevent showing irrelevant exception info in signal message

From: Eugeniy Paltsev
Date: Tue Aug 07 2018 - 09:59:52 EST

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We process signals in the end of syscall/exception handler.
It the signal is fatal we print register's content using
show_regs function. show_regs() also prints information about
last exception happened.

In case of multicore system we can catch the situation when we
will print wrong information about exception. See the example:
______________________________
CPU-0: started to handle page fault
CPU-1: sent signal to process, which is executed on CPU-0
CPU-0: ended page fault handle. Started to process signal before
returnig to userspace. Process signal, which is send from
CPU-0. As th signal is fatal we call show_regs().
show_regs() will show information about last exception
which is *page fault* (instead of "trap" which is used for
signals and happened on CPU-0)

So we will get message like this:
# ./waitpid02
potentially unexpected fatal signal 8.
Path: /home/waitpid02
CPU: 0 PID: 100 Comm: waitpid02 Not tainted 4.10.0-rc4 #2
task: 9f11c200 task.stack: 9f3ae000

[ECR ]: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x000123ec
[EFA ]: 0x00000000
[BLINK ]: 0x123ea
[ERET ]: 0x123ec
@off 0x123ec in [/home/waitpid02]
VMA: 0x00010000 to 0x00016000
[STAT32]: 0x80080882 : IE U
BTA: 0x000123ea SP: 0x5ffd3db0 FP: 0x00000000
LPS: 0x20031684 LPE: 0x2003169a LPC: 0x00000006
[-----other-info-----]

This message is confusing because it show information about page fault
( [ECR ]: 0x00050200 => Invalid Write ) which is absolutely irrelevant
to signal.

This situation was reproduced with waitpid02 LTP test.
_____________________________

So remove printing information about exceptions from show_regs()
to avoid confusing messages. Print information about exceptions
only in required places instead of show_regs()

Now we don't print information about exceptions if signal is simply
send by another userspace app. So in case of waitpid02 we will print
next message:
_____________________________
# ./waitpid02
potentially unexpected fatal signal 8.
Path: /root/waitpid02
CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
[ECR ]: 0x00050100
[EFA ]: 0x00000000
[BLINK ]: 0x20001486
[-----other-info-----]
_____________________________

This patch fix
STAR 9001146055: waitpid02: Invalid Write @ 0x00000000 by insn @ 0x000123ec

NOTE:
To be more clear I give examples of different faults (signal-based,
userspace/kernelspace exception-based) with different values of
"/proc/sys/kernel/print-fatal-signals" option.

0) NULL pointer access from user space, print-fatal-signals == 1:
------------>8---------------
# ./arc_hell
Exception: arc_hell[103]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
potentially unexpected fatal signal 11.
Path: /root/arc_hell
CPU: 1 PID: 103 Comm: arc_hell Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
[ECR ]: 0x00050100
[EFA ]: 0x00000000
[BLINK ]: 0x20039ef8
[ERET ]: 0x2003a35c
[STAT32]: 0x80080882 : IE U
BTA: 0x2003a358 SP: 0x5fa27dc4 FP: 0x5fa27de8
LPS: 0x2003a628 LPE: 0x2003a62c LPC: 0x00000000
r00: 0x00000000 r01: 0x200740b0 r02: 0x00000001
r03: 0x00000007 r04: 0x80808080 r05: 0x2f2f2f2f
r06: 0x7c7a2f43 r07: 0x00000000 r08: 0x1a131100
r09: 0x2008b1e0 r10: 0x20003a5c r11: 0x20004038
r12: 0x20039ef8 r13: 0x200740b0 r14: 0x00000000
r15: 0x200740b0 r16: 0x00000000 r17: 0x0007d468
r18: 0x0009313a r19: 0x00000000 r20: 0x0009c22c
r21: 0x0009c23c r22: 0x0009ab64 r23: 0x00000000
r24: 0x0009dfc5 r25: 0x20004b70

Segmentation fault
------------>8---------------

1) NULL pointer access from user space, print-fatal-signals == 0:
------------>8---------------
# ./arc_hell
Exception: arc_hell[107]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
Segmentation fault
------------>8---------------

2) Process killed by signal (waitpid02 test), print-fatal-signals == 1:
------------>8---------------
# ./waitpid02
potentially unexpected fatal signal 8.
Path: /root/waitpid02
CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
[ECR ]: 0x00050100
[EFA ]: 0x00000000
[BLINK ]: 0x20001486
[ERET ]: 0x2000146c
[STAT32]: 0x80080082 : IE U
BTA: 0x20000fc4 SP: 0x5fa21d64 FP: 0x00000000
LPS: 0x200524a0 LPE: 0x200524b6 LPC: 0x00000006
r00: 0x2000c0dc r01: 0x00000018 r02: 0x0001159a
r03: 0x00000001 r04: 0x00000000 r05: 0x00000045
r06: 0x0000004e r07: 0x01010101 r08: 0x000000dc
r09: 0x200a31e0 r10: 0x20003a5c r11: 0x20004038
r12: 0x20001486 r13: 0x20004174 r14: 0x07ca2bc0
r15: 0x20004078 r16: 0x00000000 r17: 0x20004038
r18: 0x00000001 r19: 0x00000000 r20: 0x0001159a
r21: 0x00000001 r22: 0x00000000 r23: 0x00000004
r24: 0x2000d1fc r25: 0x20004cd0
------------>8---------------

3) Process killed by signal (waitpid02 test), print-fatal-signals == 0:
------------>8---------------
# ./waitpid02
------------>8---------------

4) NULL pointer access from kernel space, regardless print-fatal-signals
value:
------------>8---------------
Oops
Exception: at stmmac_dvr_probe+0x40/0x7e0:
ECR: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x90575254
Path: (null)
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #11
[EFA ]: 0x00000000
[BLINK ]: stmmac_dvr_probe+0x2a/0x7e0
[ERET ]: stmmac_dvr_probe+0x40/0x7e0
[STAT32]: 0x80080402 : IE K
BTA: 0x9057523e SP: 0xbf02be40 FP: 0x00000000
LPS: 0x9073dbcc LPE: 0x9073dbe0 LPC: 0x00000000
r00: 0xbf1f0000 r01: 0x00000000 r02: 0x00000008
r03: 0x00000000 r04: 0x00000064 r05: 0x00000000
r06: 0x00000003 r07: 0x00000004 r08: 0x01010101
r09: 0x00000031 r10: 0xbf1f0006 r11: 0x00000000
r12: 0x9057523e

Stack Trace:
stmmac_dvr_probe+0x40/0x7e0
dwmac_generic_probe+0x50/0xbc
platform_drv_probe+0x26/0x5c
really_probe+0x3b0/0x464
__driver_attach+0xd4/0xd8
bus_for_each_dev+0x3a/0x70
bus_add_driver+0x12a/0x18c
driver_register+0x56/0xe8
do_one_initcall+0x2e/0x118
kernel_init_freeable+0x102/0x194
------------>8---------------

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
---

NOTE:
This patch has prerequisites:
https://www.mail-archive.com/linux-snps-arc@xxxxxxxxxxxxxxxxxxx/msg03938.html
https://www.mail-archive.com/linux-snps-arc@xxxxxxxxxxxxxxxxxxx/msg03937.html

Changes v1->v2:
* Change format of message about exception.

arch/arc/include/asm/bug.h | 1 +
arch/arc/kernel/traps.c | 1 +
arch/arc/kernel/troubleshoot.c | 51 +++++++++++++++++++++++++++++++++---------
arch/arc/mm/fault.c | 2 ++
4 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/arch/arc/include/asm/bug.h b/arch/arc/include/asm/bug.h
index 21ec82466d62..b68f7f82f2d8 100644
--- a/arch/arc/include/asm/bug.h
+++ b/arch/arc/include/asm/bug.h
@@ -16,6 +16,7 @@
struct task_struct;

void show_regs(struct pt_regs *regs);
+void show_exception_mesg(struct pt_regs *regs);
void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs);
void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
unsigned long address);
diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
index b123558bf0bb..5d83b2fe5f12 100644
--- a/arch/arc/kernel/traps.c
+++ b/arch/arc/kernel/traps.c
@@ -50,6 +50,7 @@ unhandled_exception(const char *str, struct pt_regs *regs, siginfo_t *info)
tsk->thread.fault_address = (__force unsigned int)info->si_addr;

force_sig_info(info->si_signo, info, tsk);
+ show_exception_mesg(regs);

} else {
/* If not due to copy_(to|from)_user, we are doomed */
diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index e8d9fb452346..fdfba1942a06 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -101,13 +101,13 @@ static void show_faulting_vma(unsigned long address, char *buf)
if (IS_ERR(nm))
nm = "?";
}
- pr_info(" @off 0x%lx in [%s]\n"
- " VMA: 0x%08lx to 0x%08lx\n",
+
+ pr_cont("[off 0x%lx in %s, VMA: %08lx:%08lx] ",
vma->vm_start < TASK_UNMAPPED_BASE ?
address : address - vma->vm_start,
nm, vma->vm_start, vma->vm_end);
} else
- pr_info(" @No matching VMA found\n");
+ pr_cont("[No matching VMA found] ");

up_read(&active_mm->mmap_sem);
}
@@ -117,7 +117,7 @@ static void show_ecr_verbose(struct pt_regs *regs)
unsigned int vec, cause_code;
unsigned long address;

- pr_info("\n[ECR ]: 0x%08lx => ", regs->event);
+ pr_cont("\n ECR: 0x%08lx => ", regs->event);

/* For Data fault, this is data address not instruction addr */
address = current->thread.fault_address;
@@ -165,10 +165,42 @@ static void show_ecr_verbose(struct pt_regs *regs)
}
}

+static inline void show_exception_mesg_u(struct pt_regs *regs)
+{
+ struct task_struct *tsk = current;
+ char *buf;
+
+ pr_info("Exception: %s[%d]: at %pS ",
+ tsk->comm, task_pid_nr(tsk), (void *)regs->ret);
+
+ buf = (char *)__get_free_page(GFP_NOWAIT);
+ if (buf) {
+ show_faulting_vma(regs->ret, buf);
+ free_page((unsigned long)buf);
+ }
+
+ show_ecr_verbose(regs);
+}
+
+static inline void show_exception_mesg_k(struct pt_regs *regs)
+{
+ pr_info("Exception: at %pS:", (void *)regs->ret);
+
+ show_ecr_verbose(regs);
+}
+
/************************************************************************
* API called by rest of kernel
***********************************************************************/

+void show_exception_mesg(struct pt_regs *regs)
+{
+ if (user_mode(regs))
+ show_exception_mesg_u(regs);
+ else
+ show_exception_mesg_k(regs);
+}
+
void show_regs(struct pt_regs *regs)
{
struct task_struct *tsk = current;
@@ -182,15 +214,10 @@ void show_regs(struct pt_regs *regs)
print_task_path_n_nm(tsk, buf);
show_regs_print_info(KERN_INFO);

- show_ecr_verbose(regs);
-
- pr_info("[EFA ]: 0x%08lx\n[BLINK ]: %pS\n[ERET ]: %pS\n",
- current->thread.fault_address,
+ pr_info("[ECR ]: 0x%08lx\n[EFA ]: 0x%08lx\n[BLINK ]: %pS\n[ERET ]: %pS\n",
+ regs->event, current->thread.fault_address,
(void *)regs->blink, (void *)regs->ret);

- if (user_mode(regs))
- show_faulting_vma(regs->ret, buf); /* faulting code, not data */
-
pr_info("[STAT32]: 0x%08lx", regs->status32);

#define STS_BIT(r, bit) r->status32 & STATUS_##bit##_MASK ? #bit" " : ""
@@ -233,6 +260,8 @@ void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
/* Show fault description */
pr_info("\n%s\n", str);

+ show_exception_mesg(regs);
+
/* Caller and Callee regs */
show_regs(regs);

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index b884bbd6f354..d9c6958a1702 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -202,6 +202,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
/* info.si_code has been set above */
info.si_addr = (void __user *)address;
force_sig_info(SIGSEGV, &info, tsk);
+ show_exception_mesg(regs);
return;
}

@@ -241,4 +242,5 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
info.si_code = BUS_ADRERR;
info.si_addr = (void __user *)address;
force_sig_info(SIGBUS, &info, tsk);
+ show_exception_mesg(regs);
}
--
2.14.4

Next message: Boris Ostrovsky: "Re: [PATCH 0/4] xen: various cleanups"
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