From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v5 3/8] arm: fixmap: implement __set_fixmap()
Date: Wed, 10 Sep 2014 18:51:26 +0100 [thread overview]
Message-ID: <20140910175126.GJ1710@arm.com> (raw)
In-Reply-To: <CAGXu5jJoW-B7WwuFUhbN4e1aL-HVxa9x4da9hB9DcCGEXVLgzw@mail.gmail.com>
Hi Kees,
On Tue, Sep 09, 2014 at 03:33:11PM +0100, Kees Cook wrote:
> On Tue, Sep 9, 2014 at 5:38 AM, Will Deacon <will.deacon@arm•com> wrote:
> > On Mon, Sep 08, 2014 at 11:40:43PM +0100, Kees Cook wrote:
> >> Ah, so it was, yes! Will, which version of this logic would you prefer?
> >
> > I still don't think we're solving the general problem here -- we're actually
> > just making the ftrace case work. It is perfectly possible for another CPU
> > to undergo a TLB miss and refill whilst the page table is being modified by
> > the CPU with preemption disabled. In this case, a local tlb flush won't
> > invalidate that entry on the other core, and we have no way of knowing when
> > the original permissions are actually observed across the system.
>
> The fixmap is used by anything doing patching _except_ ftrace,
> actually. It's used by jump labels, kprobes, and kgdb. This code is
> the general case. Access to set_fixmap is done via the kernel patching
> interface: patch_text().
>
> Right now, the patch_text interface checks cache_ops_need_broadcast(),
> and conditionally runs under stop_machine(). We could make this
> unconditional, and we'll avoid any problem with TLB misses on another
> CPU.
Yes, it we always use stop_machine, that solves the TLB broadcast problem
and we could do that if CONFIG_ARM_ERRATA_798181 is set.
> > So I think we need to figure out a way to invalidate the TLB properly. What
> > do architectures that use IPIs for TLB broadcasting do (x86, some powerpc,
> > mips, ...)? They must have exactly the same problem.
>
> I don't think this should be done at the set_fixmap level, as it is
> more a primitive. I think making sure patch_text() always works would
> be best. What do you think of using an unconditional stop_machine()
> instead?
Why not move the TLB invalidation into patch_text, then we can do
stop_machine if IS_ENABLED(CONFIG_ARM_ERRATA_798181) ||
tlb_ops_need_broadcast()?
Then that just leaves ftrace.
Will
next prev parent reply other threads:[~2014-09-10 17:51 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-03 21:57 [PATCH v5 0/8] arm: support CONFIG_RODATA Kees Cook
2014-09-03 21:57 ` [PATCH v5 1/8] arm: use generic fixmap.h Kees Cook
2014-09-03 21:57 ` [PATCH v5 2/8] ARM: expand fixmap region to 3MB Kees Cook
2014-09-03 21:57 ` [PATCH v5 3/8] arm: fixmap: implement __set_fixmap() Kees Cook
2014-09-04 17:03 ` Will Deacon
2014-09-04 17:23 ` Kees Cook
2014-09-04 17:27 ` Will Deacon
2014-09-05 19:41 ` Kees Cook
2014-09-08 10:39 ` Will Deacon
2014-09-08 18:38 ` Kees Cook
2014-09-08 19:16 ` Kees Cook
2014-09-08 21:55 ` Rabin Vincent
2014-09-08 22:40 ` Kees Cook
2014-09-09 12:38 ` Will Deacon
2014-09-09 14:33 ` Kees Cook
2014-09-10 17:51 ` Will Deacon [this message]
2014-09-11 15:27 ` Kees Cook
2014-09-11 16:05 ` Kees Cook
2014-09-11 16:16 ` Will Deacon
2014-09-11 16:27 ` Kees Cook
2014-09-03 21:57 ` [PATCH v5 4/8] arm: use fixmap for text patching when text is RO Kees Cook
2014-09-03 21:57 ` [PATCH v5 5/8] ARM: kexec: Make .text R/W in machine_kexec Kees Cook
2014-09-03 21:57 ` [PATCH v5 6/8] arm: kgdb: Handle read-only text / modules Kees Cook
2014-09-03 21:57 ` [PATCH v5 7/8] ARM: mm: allow non-text sections to be non-executable Kees Cook
2014-09-03 21:57 ` [PATCH v5 8/8] ARM: mm: allow text and rodata sections to be read-only Kees Cook
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