linux-kernel - Re: [PATCH] x86/kprobes: Simplify alloc_insn_page() with __vmalloc_node

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Date:   Wed, 14 Apr 2021 16:13:14 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/kprobes: Simplify alloc_insn_page() with
 __vmalloc_node_range

On Wed, Apr 14, 2021 at 05:22:58PM +0900, Masami Hiramatsu wrote:
> Hi Jisheng,
> 
> On Wed, 14 Apr 2021 15:27:28 +0800
> Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:
> 
> \
> > > 
> > > On Tue, 13 Apr 2021 18:03:24 +0800
> > > Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:
> > >   
> > > > Use the __vmalloc_node_range() to simplify x86's alloc_insn_page() 
> > > > implementation.  
> > > 
> > > Have you checked this is equivarent to the original code on all 
> > > architecture? IIRC, some arch has a special module_alloc(),  
> > 
> > > Indeed, this isn't equivarent to the original code. FWICT, the differences on x86 are:
> > 
> > > 1) module_alloc() allocates a special vmalloc range
> > > 2) module_alloc() randomizes the return address via. module_load_offset()
> > > 3) module_alloc() also supports kasan instrumentation by kasan_module_alloc()
> > 
> > > But I'm not sure whether the above differences are useful for kprobes ss
> > > insn slot page or not. Take 1) for example, special range in module_alloc
> > > is due to relative jump limitation, modules need to call kernel .text. does
> > > kprobes ss ins slot needs this limitation too?
> > 
> > Oops, I found this wonderful thread:
> > https://www.lkml.org/lkml/2020/7/28/1413
> > 
> > So kprobes ss ins slot page "must be in the range of relative branching only
> > for x86 and arm"
> 
> Yes, at this moment. (Not sure we can introduce similar feature on other arch too)
> 
> > 
> > And Jarkko's "arch/x86: kprobes: Remove MODULES dependency" series look
> > much better. The last version is v5, I'm not sure whether Jarkko will
> > send new version to mainline the series.
> 
> I hope so. If module_alloc() itself is implemented on the generic text_alloc(),
> I can replace the module_alloc() with text_alloc(). 

I can of course look into this too. Right now in two vacation coming back
end of this month.

/Jarkko