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

From: Eugeniy Paltsev
Date: Mon Oct 01 2018 - 12:50:51 EST

Hi Vineet,

any chance you could look at this?
Otherwise we will both forget what it is all about :)

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);
> }
--
Eugeniy Paltsev