linux-kernel - Re: [PATCH 2/2] ARM: mm: make text and rodata read-only

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Date:	Mon, 14 Apr 2014 23:08:07 +0200
From:	Rabin Vincent <rabin@....in>
To:	Kees Cook <keescook@...omium.org>
Cc:	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Alexander Holler <holler@...oftware.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] ARM: mm: make text and rodata read-only

On Tue, Apr 08, 2014 at 01:19:01PM -0700, Kees Cook wrote:
> > To prevent any stale entries being used indefinitely, perhaps the all
> > CPU TLB flush can be inserted into
> > ftrace_arch_code_modify_post_process(), which is called after the
> > stop_machine() and which is where x86 for example makes the entries
> > read-only again.
> 
> Do you mean something like this?

Yes, something like that should probably be sufficient.

> 
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index ea446ae09c89..b8c75e45a950 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -90,6 +90,8 @@ int ftrace_arch_code_modify_prepare(void)
>  int ftrace_arch_code_modify_post_process(void)
>  {
>         set_all_modules_text_ro();
> +       /* Make sure any TLB misses during machine stop are cleared. */
> +       flush_tlb_all();
>         return 0;
>  }
--
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