From: Jann Horn <jannh@google.com>
To: Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@intel.com>
Cc: mhiramat@kernel.org, Kees Cook <keescook@chromium.org>,
Nadav Amit <nadav.amit@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Paolo Bonzini <pbonzini@redhat.com>,
jkosina@suse.cz, Will Deacon <will.deacon@arm.com>,
benh@au1.ibm.com, npiggin@gmail.com,
"the arch/x86 maintainers" <x86@kernel.org>,
Borislav Petkov <bp@alien8.de>, Rik van Riel <riel@surriel.com>,
Adin Scannell <ascannell@google.com>,
kernel list <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
"David S. Miller" <davem@davemloft.net>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: TLB flushes on fixmap changes
Date: Mon, 27 Aug 2018 11:55:00 +0200 [thread overview]
Message-ID: <CAG48ez2sn_5a1HFXpDjLHmHvp49iLn06isPwAati26Y47r2ttw@mail.gmail.com> (raw)
In-Reply-To: <20180827081329.GZ24124@hirez.programming.kicks-ass.net>
On Mon, Aug 27, 2018 at 10:13 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Aug 27, 2018 at 12:03:05PM +0900, Masami Hiramatsu wrote:
> > On Sun, 26 Aug 2018 11:09:58 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
>
> > > FWIW, before text_poke_bp(), text_poke() would only be used from
> > > stop_machine, so all the other CPUs would be stuck busy-waiting with
> > > IRQs disabled. These days, yeah, that's lots more dodgy, but yes
> > > text_mutex should be serializing all that.
> >
> > I'm still not sure that speculative page-table walk can be done
> > over the mutex. Also, if the fixmap area is for aliasing
> > pages (which always mapped to memory), what kind of
> > security issue can happen?
>
> So suppose CPU-A is doing the text_poke (let's say through text_poke_bp,
> such that other CPUs get to continue with whatever they're doing).
>
> While at that point, CPU-B gets an interrupt, and the CPU's
> branch-trace-buffer for the IRET points to / near our fixmap. Then the
> CPU could do a speculative TLB fill based on the BTB value, either
> directly or indirectly (through speculative driven fault-ahead) of
> whatever is in te fixmap at the time.
Worse: The way academics have been defeating KASLR for a while is
based on TLB fills for kernel addresses, triggered from userspace.
Quoting https://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf :
| Additionally, even if a permission error occurs, this still allows to
| launch address translations and, hence, generate valid TLB entries
| by accessing privileged kernel space memory from user mode.
This was actually part of the original motivation for KAISER/KPTI.
Quoting https://gruss.cc/files/kaiser.pdf :
| Modern operating system kernels employ address space layout
| randomization (ASLR) to prevent control-flow hijacking attacks and
| code-injection attacks. While kernel security relies fundamentally
on preventing
| access to address information, recent attacks have shown that the
| hardware directly leaks this information.
I believe that PTI probably prevents this way of directly triggering
TLB fills for now (under the assumption that hyperthreads with equal
CR3 don't share TLB entries), but I would still assume that an
attacker can probably trigger TLB fills for arbitrary addresses
anytime. And at some point in the future, I believe people would
probably like to be able to disable PTI again?
> Then CPU-A completes the text_poke and only does a local TLB invalidate
> on CPU-A, leaving CPU-B with an active translation.
>
> *FAIL*
next prev parent reply other threads:[~2018-08-27 9:55 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-22 15:30 [PATCH 0/4] x86: TLB invalidate fixes Peter Zijlstra
2018-08-22 15:30 ` [PATCH 1/4] x86/mm/tlb: Revert the recent lazy TLB patches Peter Zijlstra
2018-08-22 21:37 ` Linus Torvalds
2018-08-22 22:11 ` Rik van Riel
2018-08-22 15:30 ` [PATCH 2/4] mm/tlb: Remove tlb_remove_table() non-concurrent condition Peter Zijlstra
2018-08-23 3:31 ` Nicholas Piggin
2018-08-23 3:35 ` Linus Torvalds
2018-08-23 3:44 ` Linus Torvalds
2018-08-23 4:16 ` Nicholas Piggin
2018-08-23 4:54 ` Linus Torvalds
2018-08-23 5:15 ` Nicholas Piggin
2018-08-24 8:42 ` Peter Zijlstra
2018-08-23 13:40 ` Will Deacon
2018-08-22 15:30 ` [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE Peter Zijlstra
2018-08-22 15:55 ` Peter Zijlstra
2018-08-23 3:45 ` Nicholas Piggin
2018-08-23 3:59 ` Linus Torvalds
2018-08-23 4:33 ` Nicholas Piggin
2018-08-23 5:03 ` Linus Torvalds
2018-08-23 5:58 ` Nicholas Piggin
2018-08-23 4:54 ` Benjamin Herrenschmidt
2018-08-23 5:11 ` Linus Torvalds
2018-08-23 5:20 ` Linus Torvalds
2018-08-23 6:48 ` Martin Schwidefsky
2018-08-23 5:21 ` Benjamin Herrenschmidt
2018-08-23 6:15 ` Nicholas Piggin
2018-08-23 13:39 ` Will Deacon
2018-08-24 8:47 ` Peter Zijlstra
2018-08-24 11:32 ` Peter Zijlstra
2018-08-24 11:39 ` Peter Zijlstra
2018-08-27 5:00 ` Nicholas Piggin
2018-08-27 7:47 ` Peter Zijlstra
2018-08-27 8:04 ` Nicholas Piggin
2018-08-27 8:09 ` Benjamin Herrenschmidt
2018-08-27 8:20 ` Peter Zijlstra
2018-08-27 8:54 ` Nicholas Piggin
2018-08-27 9:02 ` Nicholas Piggin
2018-08-27 22:13 ` Benjamin Herrenschmidt
2018-08-27 13:36 ` Rik van Riel
2018-08-27 14:29 ` Nicholas Piggin
2018-08-27 8:57 ` removig ia64, was: " Christoph Hellwig
2018-08-27 11:28 ` Peter Zijlstra
2018-08-27 11:45 ` Jason Duerstock
2018-08-27 11:00 ` Peter Zijlstra
2018-08-30 0:13 ` Vineet Gupta
2018-08-30 10:23 ` Peter Zijlstra
2018-08-24 17:26 ` Nadav Amit
2018-08-24 18:04 ` Peter Zijlstra
2018-08-24 18:35 ` TLB flushes on fixmap changes Nadav Amit
2018-08-24 19:31 ` Linus Torvalds
2018-08-24 20:24 ` Nadav Amit
2018-08-25 0:58 ` Linus Torvalds
2018-08-25 2:29 ` nadav.amit
2018-08-25 4:23 ` Andy Lutomirski
2018-08-26 2:23 ` Masami Hiramatsu
2018-08-26 4:21 ` Andy Lutomirski
2018-08-26 4:43 ` Kees Cook
2018-08-26 5:53 ` Nadav Amit
2018-08-26 14:20 ` Andy Lutomirski
2018-08-26 16:47 ` Kees Cook
2018-08-26 17:25 ` Andy Lutomirski
2018-08-26 20:15 ` Thomas Gleixner
2018-08-26 22:03 ` Kees Cook
2018-08-26 22:15 ` Matthew Wilcox
2018-08-26 22:29 ` Jann Horn
2018-08-26 9:09 ` Peter Zijlstra
2018-08-27 3:03 ` Masami Hiramatsu
2018-08-27 3:26 ` Nadav Amit
2018-08-27 8:05 ` Masami Hiramatsu
2018-08-27 17:34 ` Nadav Amit
2018-08-27 18:45 ` Andy Lutomirski
2018-08-27 18:54 ` Nadav Amit
2018-08-27 18:58 ` Andy Lutomirski
2018-08-27 19:10 ` Nadav Amit
2018-08-27 19:43 ` Nadav Amit
2018-08-27 19:58 ` Andy Lutomirski
2018-08-27 20:16 ` Nadav Amit
2018-08-27 21:55 ` Nadav Amit
2018-08-27 22:32 ` Andy Lutomirski
2018-08-27 22:54 ` Nadav Amit
2018-08-27 23:01 ` Andy Lutomirski
2018-08-28 8:49 ` Masami Hiramatsu
2018-08-28 17:33 ` Nadav Amit
2018-08-27 8:13 ` Peter Zijlstra
2018-08-27 9:39 ` Masami Hiramatsu
2018-08-27 9:55 ` Jann Horn [this message]
2018-08-26 22:48 ` Jann Horn
2018-08-24 8:35 ` [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE Peter Zijlstra
2018-08-24 13:13 ` Peter Zijlstra
2018-08-24 13:14 ` Peter Zijlstra
2018-08-24 15:49 ` Will Deacon
2018-08-23 23:31 ` Will Deacon
2018-08-22 21:34 ` Linus Torvalds
2018-08-23 8:46 ` Nicholas Piggin
2018-08-22 15:30 ` [PATCH 4/4] x86/mm: Only use tlb_remove_table() for paravirt Peter Zijlstra
2018-08-22 22:12 ` Eduardo Valentin
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