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By checking the raw data below, will see the lr (fp+8) data show the pointer which already been replaced by PAC prefix.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