Re: [PATCH 4/4] kprobes: Remove core dependency on modules

[Mark Rutland]

On Tue, Mar 26, 2024 at 04:36:24PM +0000, Mark Rutland wrote:
> From: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> 
> Tracing with kprobes while running a monolithic kernel is currently
> impossible because KPROBES depends on MODULES. While this dependency is
> necessary when KPROBES_USE_MODULE_ALLOC=y, all the other module-specific
> code only exist to handle the case when MODULES=y, and can be hidden
> behind ifdeffery.
> 
> Add the necessary ifdeffery, and remove the dependency on MODULES=N when
> KPROBES_USE_MODULE_ALLOC=n.
> 
> Currently this allows kprobes to be used when CONFIG_MODULES=n on arm64
> and riscv, and other architectures can enable support by implementing
> their own kprobes_alloc_insn_page() and kprobes_free_insn_page() which
> do not depend on MODULES.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Link: https://lore.kernel.org/all/20240326012102.27438-1-jarkko@xxxxxxxxxx/
> [Mark: Remove execmem changes, depend on !KPROBES_USE_MODULE_ALLOC]
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
> ---
>  arch/Kconfig                |  2 +-
>  kernel/kprobes.c            | 12 +++++++++++-
>  kernel/trace/trace_kprobe.c | 15 +++++++++++++--
>  3 files changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 85bb59f7b8c07..cf43de9ffb5b9 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -52,7 +52,7 @@ config GENERIC_ENTRY
>  
>  config KPROBES
>  	bool "Kprobes"
> -	depends on MODULES
> +	depends on MODULES || !KPROBES_USE_MODULE_ALLOC

Whoops; that should be:

	depends on MODULES || HAVE_KPROBES_ALLOC

.. with similar fixups in the commit message to describe HAVE_KPROBES_ALLOC
rather than KPROBES_USE_MODULE_ALLOC (which does not exist in any version of
the series that got sent to the list).

I'll send a v2 with that fixed (and the other changes from Jarkko's v7 base
patch) once I've locally tested that for architectures with and without
HAVE_KPROBES_ALLOC.

Mark.