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

From: Vineet Gupta
Date: Mon Oct 01 2018 - 12:56:31 EST

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In reply to: Eugeniy Paltsev: "Re: [PATCH v2] ARC: prevent showing irrelevant exception info in signal message"
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On 10/01/2018 09:50 AM, Eugeniy Paltsev wrote:
> Hi Vineet,
>
> any chance you could look at this?
> Otherwise we will both forget what it is all about :)

I was busy with non Linux stuff for quite some time - hopefully that should be
wrapped up and I can get back to tending you ;-)

-Vineet

>
> On Tue, 2018-08-07 at 16:59 +0300, Eugeniy Paltsev wrote:
>> 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);
>> }

Next message: Paul Burton: "Re: [PATCH] MAINTAINERS: MIPS/LOONGSON2 ARCHITECTURE - Use the normal wildcard style"
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In reply to: Eugeniy Paltsev: "Re: [PATCH v2] ARC: prevent showing irrelevant exception info in signal message"
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