问题
Ours is a PowerPC based embedded system running Linux. We are encountering a random SIGILL crash which is seen for wide variety of applications. The root-cause for the crash is zeroing out of the instruction to be executed. This indicates corruption of the text segment residing in memory. As the text segment is loaded read-only, the application cannot corrupt it. So I am suspecting some common sub-system (DMA?) causing this corruption. Since the problem takes days to reproduce (crash due to SIGILL) it is getting difficult to investigate. So to begin with I want to be able to know if and when the text segment of any application has been corrupted.
I have looked at the stack trace and all the pointers, registers are proper.
Do you guys have any suggestions how I can go about it?
Some Info:
Linux 3.12.19-rt30 #1 SMP Fri Mar 11 01:31:24 IST 2016 ppc64 GNU/Linux
(gdb) bt
0 0x10457dc0 in xxx
Disassembly output:
=> 0x10457dc0 <+80>: mr r1,r11
0x10457dc4 <+84>: blr
Instruction expected at address 0x10457dc0: 0x7d615b78
Instruction found after catching SIGILL 0x10457dc0: 0x00000000
(gdb) maintenance info sections
0x10006c60->0x106cecac at 0x00006c60: .text ALLOC LOAD READONLY CODE HAS_CONTENTS
Expected (from the application binary):
(gdb) x /32 0x10457da0
0x10457da0 : 0x913e0000 0x4bff4f5d 0x397f0020 0x800b0004
0x10457db0 : 0x83abfff4 0x83cbfff8 0x7c0803a6 0x83ebfffc
0x10457dc0 : 0x7d615b78 0x4e800020 0x7c7d1b78 0x7fc3f378
0x10457dd0 : 0x4bcd8be5 0x7fa3eb78 0x4857e109 0x9421fff0
Actual (after handling SIGILL and dumping nearby memory locations):
Faulting instruction address: 0x10457dc0
0x10457da0 : 0x913E0000
0x10457db0 : 0x83ABFFF4
=> 0x10457dc0 : 0x00000000
0x10457dd0 : 0x4BCD8BE5
0x10457de0 : 0x93E1000C
Edit:
One lead that we have is that the corruption is always occurring at an offset that ends with 0xdc0.
For e.g.
Faulting instruction address: 0x10653dc0 << printed by our application after catching SIGILL
Faulting instruction address: 0x1000ddc0 << printed by our application after catching SIGILL
flash_erase[8557]: unhandled signal 4 at 0fed6dc0 nip 0fed6dc0 lr 0fed6dac code 30001
nandwrite[8561]: unhandled signal 4 at 0fed6dc0 nip 0fed6dc0 lr 0fed6dac code 30001
awk[4448]: unhandled signal 4 at 0fe09dc0 nip 0fe09dc0 lr 0fe09dbc code 30001
awk[16002]: unhandled signal 4 at 0fe09dc0 nip 0fe09dc0 lr 0fe09dbc code 30001
getStats[20670]: unhandled signal 4 at 0fecfdc0 nip 0fecfdc0 lr 0fecfdbc code 30001
expr[27923]: unhandled signal 4 at 0fe74dc0 nip 0fe74dc0 lr 0fe74dc0 code 30001
Edit 2: Another lead is that the corruption is always occurring at physical frame number 0x00a4d. I suppose with PAGE_SIZE of 4096 this translates to physical address of 0x00A4DDC0. We are suspecting couple of our kernel drivers and investigating further. Is there any better idea (like putting hardware watchpoint) which could be more efficient? How about KASAN as suggested below?
Any help is appreciated. Thanks.
回答1:
1.) Text segment is RO, but the permissions could be changed by mprotect, you can check that if you think it is possible
2.) If it is kernel problem:
- Run kernel with KASAN and KUBSAN (undefined behaviour) sanitizers
- Focus on drivers code not included in mainline
- The hint here is one byte corruption. Maybe i'm wrong, but it means that DMA is not to blame. It looks like some kind of invalid store.
3.) Hardware. I think, your problem looks like a hardware problem (RAM issue).
- You can try to decrease RAM system frequency in bootloader
- Check if this problem reproduces on stable mainline software, that is how you can prove that it's it
来源：https://stackoverflow.com/questions/39010931/debugging-a-nasty-sigill-crash-text-segment-corruption