From: Jann Horn <jannh@google.com>
To: Andy Lutomirski <luto@kernel.org>, Kees Cook <keescook@chromium.org>
Cc: mhiramat@kernel.org, Nadav Amit <nadav.amit@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Paolo Bonzini <pbonzini@redhat.com>,
jkosina@suse.cz, Peter Zijlstra <peterz@infradead.org>,
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>,
Dave Hansen <dave.hansen@intel.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 00:48:13 +0200 [thread overview]
Message-ID: <CAG48ez1cYsa+5Grbzp0oGTFyjqE4pR-Qe9gb=0TKc9Q5HuOpmA@mail.gmail.com> (raw)
In-Reply-To: <CALCETrXPaX-+R6Z9LqZp0uOVmq-TUX_ksPbUL7mnfbdqo6z2AA@mail.gmail.com>
On Sun, Aug 26, 2018 at 6:21 AM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Sat, Aug 25, 2018 at 7:23 PM, Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > On Fri, 24 Aug 2018 21:23:26 -0700
> > Andy Lutomirski <luto@kernel.org> wrote:
> >> Couldn't text_poke() use kmap_atomic()? Or, even better, just change CR3?
> >
> > No, since kmap_atomic() is only for x86_32 and highmem support kernel.
> > In x86-64, it seems that returns just a page address. That is not
> > good for text_poke, since it needs to make a writable alias for RO
> > code page. Hmm, maybe, can we mimic copy_oldmem_page(), it uses ioremap_cache?
> >
>
> I just re-read text_poke(). It's, um, horrible. Not only is the
> implementation overcomplicated and probably buggy, but it's SLOOOOOW.
> It's totally the wrong API -- poking one instruction at a time
> basically can't be efficient on x86. The API should either poke lots
> of instructions at once or should be text_poke_begin(); ...;
> text_poke_end();.
>
> Anyway, the attached patch seems to boot. Linus, Kees, etc: is this
> too scary of an approach? With the patch applied, text_poke() is a
> fantastic exploit target. On the other hand, even without the patch
> applied, text_poke() is every bit as juicy.
Twiddling CR0.WP is incompatible with Xen PV, right? It can't let you
do it because you're not actually running in ring 0 (but in ring 1 or
3), so CR0.WP has no influence on what you can access; and it must not
let you bypass write protection because you have read-only access to
host page tables. I think this code has to be compatible with Xen PV,
right?
In theory Xen PV could support this by emulating X86 instructions, but
I don't see anything related to CR0.WP in their emulation code. From
xen/arch/x86/pv/emul-priv-op.c:
case 0: /* Write CR0 */
if ( (val ^ read_cr0()) & ~X86_CR0_TS )
{
gdprintk(XENLOG_WARNING,
"Attempt to change unmodifiable CR0 flags\n");
break;
}
do_fpu_taskswitch(!!(val & X86_CR0_TS));
return X86EMUL_OKAY;
Having a special fallback path for "patch kernel code while running
under Xen PV" would be kinda ugly.
next prev parent reply other threads:[~2018-08-26 22:48 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
2018-08-26 22:48 ` Jann Horn [this message]
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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