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

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Date:   Wed, 14 Apr 2021 15:27:28 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     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

Jisheng Zhang wrote:

> 
> 
> Hi,  

Hi

> 
> 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"

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.

thanks