On 2023-03-26 11:00, yashvardhan kukreti wrote:
Hi Mathew,
I have a question about this patch for lttng-modules and the use of
register_kprobe() to fetch the function ptr.
The question in this regard is especially from PPC64 ELF_ABI_v1
perspective.
The functions on PPC64 are accessed via the Function descriptor
while what register_kprobes returns is the entry point of the function.
Hence using the return pointer tends to interpret the addr as the
address of the function descriptor and dereferences the ppc_inst as
the function entry point and crashes
[ 4145.483594] kernel tried to execute exec-protected page
(7c0802a6fb81ffe0) - exploit attempt? (uid: 0)
here 7c0802a6 is the mfspr instruction from the code text section of
the kallsyms_lookup_name()
note for PPC_ELF_ABI_v1 the register_kprobes() searches for the dot
variant of the symbol and only in case if cannot find the dot
variant looks for the normal symbol.
register_kprobe() -> kprobe_addr() -> kprobe_lookup_name() [arch
variant replaces weak symbol]
https://elixir.bootlin.com/linux/v5.10.174/C/ident/kprobe_lookup_name
<https://elixir.bootlin.com/linux/v5.10.174/C/ident/kprobe_lookup_name>
Please let me know if i make sense or that i may have missed something.
I have looked at the code of 2.12.8 as well and 2.12.3 verstion of
lttng-modules.
Please have a look at commits (from stable-2.12 branch of lttng-modules):
commit 53772db24facd84f1f3ddcf21a1ef5f162608721
Author: He Zhe <zhe...@windriver.com>
Date: Tue Sep 27 15:59:42 2022 +0800
wrapper: powerpc64: fix kernel crash caused by do_get_kallsyms
commit 8fe888d86ccad4226b05a536efb73d71bb091062
Author: Michael Jeanson <mjean...@efficios.com>
Date: Thu Nov 24 14:25:33 2022 -0500
fix: kallsyms wrapper on ppc64el
I suspect you'll also need this change currently in review:
https://review.lttng.org/c/lttng-modules/+/9113
Please let us know if especially this last change fixes things on your side.
Thanks,
Mathieu
Regards,
Shashank
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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