linux-kernel - Re: [PATCH 2/2] moderr: add module error injection tool

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Message-ID: <CAADnVQJ8tYSx-ujszq54m2XyecoJUgQZ6HQheTrohhfQS6Y9sQ@mail.gmail.com>
Date: Wed, 22 Jan 2025 09:02:19 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Daniel Gomez <da.gomez@...sung.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-modules@...r.kernel.org, 
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	clang-built-linux <llvm@...ts.linux.dev>, iovisor-dev <iovisor-dev@...ts.iovisor.org>, 
	gost.dev@...sung.com
Subject: Re: [PATCH 2/2] moderr: add module error injection tool

On Wed, Jan 22, 2025 at 5:12 AM Daniel Gomez <da.gomez@...sung.com> wrote:
>
> Add support for a module error injection tool. The tool
> can inject errors in the annotated module kernel functions
> such as complete_formation(), do_init_module() and
> module_enable_rodata_after_init(). Module name and module function are
> required parameters to have control over the error injection.
>
> Example: Inject error -22 to module_enable_rodata_ro_after_init for
> brd module:
>
> sudo moderr --modname=brd --modfunc=module_enable_rodata_ro_after_init \
> --error=-22 --trace
> Monitoring module error injection... Hit Ctrl-C to end.
> MODULE     ERROR FUNCTION
> brd        -22   module_enable_rodata_after_init()
>
> Kernel messages:
> [   89.463690] brd: module loaded
> [   89.463855] brd: module_enable_rodata_ro_after_init() returned -22,
> ro_after_init data might still be writable
>
> Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
> ---
>  tools/bpf/Makefile            |  13 ++-
>  tools/bpf/moderr/.gitignore   |   2 +
>  tools/bpf/moderr/Makefile     |  95 +++++++++++++++++
>  tools/bpf/moderr/moderr.bpf.c | 127 +++++++++++++++++++++++
>  tools/bpf/moderr/moderr.c     | 236 ++++++++++++++++++++++++++++++++++++++++++
>  tools/bpf/moderr/moderr.h     |  40 +++++++
>  6 files changed, 510 insertions(+), 3 deletions(-)

The tool looks useful, but we don't add tools to the kernel repo.
It has to stay out of tree.

The value of error injection is not clear to me.
Other places in the kernel use it to test paths in the kernel
that are difficult to do otherwise.
These 3 functions don't seem to be in this category.