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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
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