[Crash-utility] arm64: Fix bt command show wrong stacktrace on ramdump source

cb126yx <cb126yx@xxxxxxx> · Wed, 3 Jul 2024 17:23:55 +0800 (CST)

Hi all,
I may found a potential bug when using qcom arm64 ramdump to parse backtrace.
Unfortunately, I actually found no processes can use the bt command correctly.

Ex: when start crash tool to do analyse: # crash vmlinux --kaslr=xxx DDRCS0_0.BIN@0x0000000080000000,... --machdep vabits_actual=39

Then seen below misleading backtrace information :  
crash> bt 16930
PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"
 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4
 #1 [ffffffc034c43850] __kvm_nvhe_$d.2314 at 6be732e004cf05a0
 #2 [ffffffc034c438b0] __kvm_nvhe_$d.2314 at 86c54c6004ceff80
 #3 [ffffffc034c43950] __kvm_nvhe_$d.2314 at 55d6f96003a7b120
 #4 [ffffffc034c439f0] __kvm_nvhe_$d.2314 at 9ccec46003a80a64
 #5 [ffffffc034c43ac0] __kvm_nvhe_$d.2314 at 8cf41e6003a945c4
 #6 [ffffffc034c43b10] __kvm_nvhe_$d.2314 at a8f181e00372c818
 #7 [ffffffc034c43b40] __kvm_nvhe_$d.2314 at 6dedde600372c0d0
 #8 [ffffffc034c43b90] __kvm_nvhe_$d.2314 at 62cc07e00373d0ac
 #9 [ffffffc034c43c00] __kvm_nvhe_$d.2314 at 72fb1de00373bedc
...
     PC: 00000073f5294840   LR: 00000070d8f39ba4   SP: 00000070d4afd5d0
    X29: 00000070d4afd600  X28: b4000071efcda7f0  X27: 00000070d4afe000
    X26: 0000000000000000  X25: 00000070d9616000  X24: 0000000000000000
    X23: 0000000000000000  X22: 0000000000000000  X21: 0000000000000000
    X20: b40000728fd27520  X19: b40000728fd27550  X18: 000000702daba000
    X17: 00000073f5294820  X16: 00000070d940f9d8  X15: 00000000000000bf
    X14: 0000000000000000  X13: 00000070d8ad2fac  X12: b40000718fce5040
    X11: 0000000000000000  X10: 0000000000000070   X9: 0000000000000001
     X8: 0000000000000062   X7: 0000000000000020   X6: 0000000000000000
     X5: 0000000000000000   X4: 0000000000000000   X3: 0000000000000000
     X2: 0000000000000002   X1: 0000000000000080   X0: b40000728fd27550
    ORIG_X0: b40000728fd27550  SYSCALLNO: ffffffff  PSTATE: 40001000

By checking the raw data below, will see the lr (fp+8) data show the pointer which already been replaced by PAC prefix.

crash> bt -f
PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"
 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4
    ffffffc034c437f0: ffffffc034c43850 6be732e004cf05a4
    ffffffc034c43800: ffffffe006186108 a0ed07e004cf09c4
    ffffffc034c43810: ffffff8a1a340000 ffffff8a8d343c00
    ffffffc034c43820: ffffff89b3eada00 ffffff8b780db540
    ffffffc034c43830: ffffff89b3eada00 0000000000000000
    ffffffc034c43840: 0000000000000004 712b828118484a00
 #1 [ffffffc034c43850] __kvm_nvhe_$d.2314 at 6be732e004cf05a0
    ffffffc034c43850: ffffffc034c438b0 86c54c6004ceff84
    ffffffc034c43860: 000000708070f000 ffffffc034c43938
    ffffffc034c43870: ffffff88bd822878 ffffff89b3eada00
...

So we check the CONFIG_ARM64_PTR_AUTH and CONFIG_ARM64_PTR_AUTH_KERNEL to double check if pac mechanism been enabled on this ramdump.
Then we use vabits to figure it out.
Fix then show the right backtrace below:
crash> bt 16930
PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"
 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4
 #1 [ffffffc034c43850] __schedule at ffffffe004cf05a0
 #2 [ffffffc034c438b0] preempt_schedule_common at ffffffe004ceff80
 #3 [ffffffc034c43950] unmap_page_range at ffffffe003a7b120
 #4 [ffffffc034c439f0] unmap_vmas at ffffffe003a80a64
 #5 [ffffffc034c43ac0] exit_mmap at ffffffe003a945c4
 #6 [ffffffc034c43b10] __mmput at ffffffe00372c818
 #7 [ffffffc034c43b40] mmput at ffffffe00372c0d0
 #8 [ffffffc034c43b90] exit_mm at ffffffe00373d0ac
 #9 [ffffffc034c43c00] do_exit at ffffffe00373bedc
     PC: 00000073f5294840   LR: 00000070d8f39ba4   SP: 00000070d4afd5d0
    X29: 00000070d4afd600  X28: b4000071efcda7f0  X27: 00000070d4afe000
    X26: 0000000000000000  X25: 00000070d9616000  X24: 0000000000000000
    X23: 0000000000000000  X22: 0000000000000000  X21: 0000000000000000
    X20: b40000728fd27520  X19: b40000728fd27550  X18: 000000702daba000
    X17: 00000073f5294820  X16: 00000070d940f9d8  X15: 00000000000000bf
    X14: 0000000000000000  X13: 00000070d8ad2fac  X12: b40000718fce5040
    X11: 0000000000000000  X10: 0000000000000070   X9: 0000000000000001
     X8: 0000000000000062   X7: 0000000000000020   X6: 0000000000000000
     X5: 0000000000000000   X4: 0000000000000000   X3: 0000000000000000
     X2: 0000000000000002   X1: 0000000000000080   X0: b40000728fd27550
    ORIG_X0: b40000728fd27550  SYSCALLNO: ffffffff  PSTATE: 40001000

Let's use GENMASK to replace the pac pointer to fix it.
gki related commit url here:
https://lore.kernel.org/all/20230412160134.306148-4-mark.rutland@xxxxxxx/ 
Attachment:
0001-arm64-Fix-bt-command-show-wrong-stacktrace-on-ramdum.patch

Description: Binary data
--
Crash-utility mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxxxxxx
https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/
Contribution Guidelines: https://github.com/crash-utility/crash/wiki