linux-kernel - Re: [PATCH 08/17] x86/ftrace: set trampoline pages as executable

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Message-ID: <20190206124108.07eef568@gandalf.local.home>
Date:   Wed, 6 Feb 2019 12:41:08 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Damian Tometzki <linux_dti@...oud.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux-MM <linux-mm@...ck.org>, Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        deneen.t.dock@...el.com
Subject: Re: [PATCH 08/17] x86/ftrace: set trampoline pages as executable

On Wed, 6 Feb 2019 09:33:35 -0800
Nadav Amit <nadav.amit@...il.com> wrote:


> >> 	/* Copy ftrace_caller onto the trampoline memory */
> >> 	ret = probe_kernel_read(trampoline, (void *)start_offset, size);
> >> @@ -818,6 +820,13 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
> >> 	/* ALLOC_TRAMP flags lets us know we created it */
> >> 	ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
> >> 
> >> +	/*
> >> +	 * Module allocation needs to be completed by making the page
> >> +	 * executable. The page is still writable, which is a security hazard,
> >> +	 * but anyhow ftrace breaks W^X completely.
> >> +	 */  
> > 
> > Perhaps we should set the page to non writable after the page is
> > updated? And set it to writable only when we need to update it.  
> 
> You remember that I sent you a patch that changed all these writes into
> text_poke() and you said that I should defer it until this series is merged?
> 

And I notice that it is set to RO after this call anyway.

-- Steve