January 2019 - kernelnewbies@kernelnewbies.org

Re: Need help: how to locate failure from irq_chip subsystem
by Pintu Agarwal Jan. 18, 2019

Jan. 18, 2019

On Fri, Jan 18, 2019 at 3:54 PM Sai Prakash Ranjan <saiprakash.ranjan(a)codeaurora.org> wrote: > > Hi Pintu-san, > > On 1/18/2019 3:38 PM, Pintu Agarwal wrote: > > Hi All, > > > > Currently, I am trying to debug a boot up crash on some qualcomm > > snapdragon arm64 board with kernel 4.9. > > I could find the cause of the failure, but I am unable to locate from > > which subsystem/drivers this is getting triggered. > > If you have any ideas or suggestions to locate the issue, please let me know. > > > > This is the snapshot of crash logs: > > [ 6.907065] Unable to handle kernel NULL pointer dereference at > > virtual address 00000000 > > [ 6.973938] PC is at 0x0 > > [ 6.976503] LR is at __ipipe_ack_fasteoi_irq+0x28/0x38 > > [ 7.151078] Process qmp_aop (pid: 24, stack limit = 0xfffffffbedc18000) > > [ 7.242668] [< (null)>] (null) > > [ 7.247416] [<ffffff9469f8d2e0>] __ipipe_dispatch_irq+0x78/0x340 > > [ 7.253469] [<ffffff9469e81564>] __ipipe_grab_irq+0x5c/0xd0 > > [ 7.341538] [<ffffff9469e81d68>] gic_handle_irq+0xc0/0x154 > > > > [ 6.288581] [PINTU]: __ipipe_ack_fasteoi_irq - called > > [ 6.293698] [PINTU]: __ipipe_ack_fasteoi_irq: > > desc->irq_data.chip->irq_hold is NULL > > > > When I check, I found that the irq_hold implementation is missing in > > one of the irq_chip driver (expected by ipipe), which I am supposed to > > implement. > > > > But I am unable to locate which irq_chip driver. > > If there are any good techniques to locate this in kernel, please help. > > > > Could you please tell which QCOM SoC this board is based on? > Snapdragon 845 with kernel 4.9.x I want to know from which subsystem it is triggered:drivers/soc/qcom/ > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member > of Code Aurora Forum, hosted by The Linux Foundation

2 1

Need help: how to locate failure from irq_chip subsystem
by Pintu Agarwal Jan. 18, 2019

Jan. 18, 2019

Hi All, Currently, I am trying to debug a boot up crash on some qualcomm snapdragon arm64 board with kernel 4.9. I could find the cause of the failure, but I am unable to locate from which subsystem/drivers this is getting triggered. If you have any ideas or suggestions to locate the issue, please let me know. This is the snapshot of crash logs: [ 6.907065] Unable to handle kernel NULL pointer dereference at virtual address 00000000 [ 6.973938] PC is at 0x0 [ 6.976503] LR is at __ipipe_ack_fasteoi_irq+0x28/0x38 [ 7.151078] Process qmp_aop (pid: 24, stack limit = 0xfffffffbedc18000) [ 7.242668] [< (null)>] (null) [ 7.247416] [<ffffff9469f8d2e0>] __ipipe_dispatch_irq+0x78/0x340 [ 7.253469] [<ffffff9469e81564>] __ipipe_grab_irq+0x5c/0xd0 [ 7.341538] [<ffffff9469e81d68>] gic_handle_irq+0xc0/0x154 [ 6.288581] [PINTU]: __ipipe_ack_fasteoi_irq - called [ 6.293698] [PINTU]: __ipipe_ack_fasteoi_irq: desc->irq_data.chip->irq_hold is NULL When I check, I found that the irq_hold implementation is missing in one of the irq_chip driver (expected by ipipe), which I am supposed to implement. But I am unable to locate which irq_chip driver. If there are any good techniques to locate this in kernel, please help. Thanks, Pintu

2 1

Understanding memory fragmentation in Linux kernel
by Amit Agarwal Jan. 13, 2019

Jan. 13, 2019

Hi All, I am trying to understand memory fragmentation and how to understand and/or analyze the same. Is there some detailed documentation on pagetypeinfo and buddyinfo files present in the proc directory? Am I looking at right files to understand if the memory is fragmented. Problem Description: One of the applications does a few 200-300Mb calloc's during start-up. On one of the production servers, the application does not start up although there should be enough RAM available for application to start. I am suspecting that this is because of fragmentation and would like to confirm the same. -- Thanks, -aka

3 5

Security-What can be done in kernel to disable forever executable memory modificaton
by Lev Olshvang Jan. 12, 2019

Jan. 12, 2019

Hi All, The fact that the text segment could be modified is bad news from the security standpoint. For example, in order to set a breakpoint GDB should map a text segment with MAP_PRIVATE flag which allows kernel to ignore the dirty bit that MMU sets on this page. Somewhere in the middle of this mapping, perhaps in mprotect, permission bits of page's PTE entry are modified as well from their original RO+X to RWX I am not sure whether it is actually happening, perhaps instead new pages are allocated, sort of COW (copy on write). And here I am getting to the point : Is there any way to disable the change of permission bits of PTE? Is it possible in the hardware (ARM) or should kernel be patched? Regards to All, Happy new year. Lev.

2 1

gpio: struct gpio_chip.set_multiple\get_multiple
by Subhashini Rao Beerisetty Jan. 10, 2019

Jan. 10, 2019

Hi All, struct gpio_chip { int (*get_multiple)(struct gpio_chip *chip,unsigned long *mask, unsigned long *bits); void (*set_multiple)(struct gpio_chip *chip,unsigned long *mask, unsigned long *bits); } struct gpio_chip provides set_multiple callback to assign output values for multiple signals defined by “mask” and similarly it has get_multiple callback to read values for multiple signals defined by “mask” and stores them in “bits”. I’m using deprecated sysfs interface (/sys/class/gpio/gpiochipN – v4.4 kernel), in this kernel version I could not find any userspace control to achieve to output values for multiple PIO’s and similarly to read multiple PIO’s. Can someone clarify me on this? Thanks,

1 0

where to find the kmalloc implementation
by Carter Cheng Jan. 10, 2019

Jan. 10, 2019

Hi, I am curious where in the kernel sources would I find the kmalloc implementation? I am curious how GFP_ATOMIC option is implemented. Thanks, Carter.

2 2

How to signal kernel that shared library is not in use by any process anymore ?
by Lev Olshvang Jan. 8, 2019

Jan. 8, 2019

Hi All, I have an executable (C++) which is the exclusive user of the some shared library that it uses only during the initialization phase. I would like to free memory used by this shared library, because I am running on embedded system. How can I achieve this? I know that dlopen() will load shared library, and hope that following dlclose() will free this lib memory. 1. Still I do not know what method should be used to make dynamic linker look again into executable and resolve symbols of the newly appeared symbols ? 2. And how to tell the dynamic linker ld-linux.so to postpone the symbol resolution until dlopen() will load the library? 3. Whether to compile and link executable with this library or leave unresolved symbols? Waiting for your advises, Lev.

4 6

mount /proc at boot as read-only
by Lev Olshvang Jan. 7, 2019

Jan. 7, 2019

Hello all, I am trying to harden the embedded system. Is it possible and safe to mount /proc file system in a read-only mode and how to do this? I have embedded system with systemd where /proc is mounted rw. I suspect that systemd mounts it when it bebgns to bootsrtap user space. On my currently idle and small embedded board and on QEMU I was able to remount /proc read-only. But when I changed fstab to mount it as a read-only it is still mounted rw,relatime after reboot. So who mounts it first ? Is it hardcoded in systemd when it starts process of PID 1 or in a kernel? Regards, Lev

3 2

The Kernel knows. But how ? Did the acpi make a secret dead drop ?
by Jay Aurabind Jan. 6, 2019

Jan. 6, 2019

Hi, The subject line might be a bit dramatic, but I assure you my question is isn't. I have a 3-axis accelerometer (LIS3LV02DL) in my laptop which shows up as an input device. Since its x86, I am assuming the necessary information was encoded in ACPI Tables. But I cannot find any mention of this device in the acpi tables exposed by the kernel. I tried grepping through all the ACPI tables in /sys/firmware/acpi/tables. I was hoping to find some string that could identify the corresponding kernel drivers. But there are no hits for "lis". I suppose string based literals are not the way acpi works like in kernel device-driver matching. The driver in question is drivers/misc/lis3lv02d/lis3lv02d.c So what exactly in the ACPI triggered the kernel module lis3lv02d to be loaded ? -- Thanks and Regards, *Aurabindo J*

3 7

How to forbid user space and kernel executable pages from becoming writable?
by Lev Olshvang Jan. 5, 2019

Jan. 5, 2019

I am researching this issue and I am confused with the finding Some articles, ex https://shanetully.com/2013/12/writing-a-self-mutating-x86_64-c-program/ state that mprotect() can change protection of executable section. As I understanf pte entry has page protection bits set to RO so mprotect should change pte which is loaded to MMU/TLB. Why kernel can not refuse do perform this mprotect call(). Whu we do norhave kernel config options to forbid user-space mutable code as security feature? >From the other side, when run-time linker or elf_loader loads the executable it uses MAP_DENYWRITE which protect executable file from being overwritten. But writing to executable text will make page dirty and require the write-back which is disabled by MAP_DENYWRITE. (or it might be disable for other processes except current, I am not sure?) To add to the confusion, the following quote from the LWN articlle https://lwn.net/Articles/422487/ about CONFIG_DEBUG_SET_MODULE_RONX "Marking the kernel module pages as RO and/or NX is important not only because it is consistent with how the rest of the kernel pages are handled" Digging dipper I see that ARM since kernel version 4.11 has CONFIG_STRICT_KERNEL_RWX , and as I understand it is enforced in hardware. But I am not sure that some variant of pte_clear(), pte_mkexec(0 can not disable it. So let me cut to final qiestion: Suppose I want to cut off dynamic code instrumentation, like ftrace and friends. Is it achievable at least at ARM architecture to enforce RO+X at hardware or kernel? Thanks to all folks for reading till this point. Regards Lev

3 2