linux-kernel - Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG

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Message-Id: <D03UKZ3OIEXX.2PCKOX8NOLMKT@kernel.org>
Date: Tue, 26 Mar 2024 19:11:46 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Mark Rutland" <mark.rutland@....com>, "Masami Hiramatsu"
 <mhiramat@...nel.org>
Cc: <linux-riscv@...ts.infradead.org>, "Paul Walmsley"
 <paul.walmsley@...ive.com>, "Palmer Dabbelt" <palmer@...belt.com>, "Albert
 Ou" <aou@...s.berkeley.edu>, <linux-kernel@...r.kernel.org>, "Naveen N .
 Rao" <naveen.n.rao@...ux.ibm.com>, "Anil S Keshavamurthy"
 <anil.s.keshavamurthy@...el.com>, "David S . Miller" <davem@...emloft.net>,
 <linux-trace-kernel@...r.kernel.org>, "Calvin Owens"
 <jcalvinowens@...il.com>
Subject: Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG_MODULES=n

On Tue Mar 26, 2024 at 6:38 PM EET, Mark Rutland wrote:
> On Wed, Mar 27, 2024 at 12:24:03AM +0900, Masami Hiramatsu wrote:
> > On Tue, 26 Mar 2024 14:46:10 +0000
> > Mark Rutland <mark.rutland@....com> wrote:
> > > 
> > > On Mon, Mar 25, 2024 at 11:56:32AM +0900, Masami Hiramatsu wrote:
> > > > I think, we'd better to introduce `alloc_execmem()`,
> > > > CONFIG_HAVE_ALLOC_EXECMEM and CONFIG_ALLOC_EXECMEM at first
> > > > 
> > > >   config HAVE_ALLOC_EXECMEM
> > > > 	bool
> > > > 
> > > >   config ALLOC_EXECMEM
> > > > 	bool "Executable trampline memory allocation"
> > > > 	depends on MODULES || HAVE_ALLOC_EXECMEM
> > > > 
> > > > And define fallback macro to module_alloc() like this.
> > > > 
> > > > #ifndef CONFIG_HAVE_ALLOC_EXECMEM
> > > > #define alloc_execmem(size, gfp)	module_alloc(size)
> > > > #endif
> > > 
> > > Please can we *not* do this? I think this is abstracting at the wrong level (as
> > > I mentioned on the prior execmem proposals).
> > > 
> > > Different exectuable allocations can have different requirements. For example,
> > > on arm64 modules need to be within 2G of the kernel image, but the kprobes XOL
> > > areas can be anywhere in the kernel VA space.
> > > 
> > > Forcing those behind the same interface makes things *harder* for architectures
> > > and/or makes the common code more complicated (if that ends up having to track
> > > all those different requirements). From my PoV it'd be much better to have
> > > separate kprobes_alloc_*() functions for kprobes which an architecture can then
> > > choose to implement using a common library if it wants to.
> > > 
> > > I took a look at doing that using the core ifdeffery fixups from Jarkko's v6,
> > > and it looks pretty clean to me (and works in testing on arm64):
> > > 
> > >   https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=kprobes/without-modules
> > > 
> > > Could we please start with that approach, with kprobe-specific alloc/free code
> > > provided by the architecture?
> > 
> > OK, as far as I can read the code, this method also works and neat! 
> > (and minimum intrusion). I actually found that exposing CONFIG_ALLOC_EXECMEM
> > to user does not help, it should be an internal change. So hiding this change
> > from user is better choice. Then there is no reason to introduce the new
> > alloc_execmem, but just expand kprobe_alloc_insn_page() is reasonable.
> > 
> > Mark, can you send this series here, so that others can review/test it?
>
> I've written up a cover letter and sent that out:
>   
>   https://lore.kernel.org/lkml/20240326163624.3253157-1-mark.rutland@arm.com/
>
> Mark.

Ya, saw it thanks!

BR, Jarkko