From: Al Viro <viro@ZenIV.linux.org.uk>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Andy Lutomirski" <luto@kernel.org>,
"Christoph Hellwig" <hch@infradead.org>,
"Ingo Molnar" <mingo@kernel.org>, "Greg KH" <greg@kroah.com>,
"Thomas Garnier" <thgarnie@google.com>,
"Martin Schwidefsky" <schwidefsky@de.ibm.com>,
"Heiko Carstens" <heiko.carstens@de.ibm.com>,
"Dave Hansen" <dave.hansen@intel.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"David Howells" <dhowells@redhat.com>,
"René Nyffenegger" <mail@renenyffenegger.ch>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
"Oleg Nesterov" <oleg@redhat.com>,
"Pavel Tikhomirov" <ptikhomirov@virtuozzo.com>,
"Ingo Molnar" <mingo@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Rik van Riel" <riel@redhat.com>,
"Kees Cook" <keescook@chromium.org>,
"Josh Poimboeuf" <jpoimboe@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Brian Gerst" <brgerst@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Christian Borntraeger" <borntraeger@de.ibm.com>,
"Russell King" <linux@armlinux.org.uk>,
"Will Deacon" <will.deacon@arm.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"James Morse" <james.morse@arm.com>,
linux-s390 <linux-s390@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Linux API" <linux-api@vger.kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"Kernel Hardening" <kernel-hardening@lists.openwall.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Peter Zijlstra" <a.p.zijlstra@chello.nl>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode
Date: Wed, 10 May 2017 09:08:41 +0100 [thread overview]
Message-ID: <20170510080841.GG390@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAK8P3a2j6h2MAx3h2NCtadcFsNuFcf158F5OV1e2SK37acZRRg@mail.gmail.com>
On Wed, May 10, 2017 at 09:37:04AM +0200, Arnd Bergmann wrote:
> > How about trying to remove all of them? If we could actually get rid
> > of all of them, we could drop the arch support, and we'd get faster,
> > simpler, shorter uaccess code throughout the kernel.
BTW, not all get_user() under KERNEL_DS are plain loads. There is an
exception - probe_kernel_read().
> > The ones in kernel/compat.c are generally garbage. They should be
> > using compat_alloc_user_space(). Ditto for kernel/power/user.c.
>
> compat_alloc_user_space() has some problems too, it adds
> complexity to a rarely-tested code path and can add some noticeable
> overhead in cases where user space access is slow because of
> extra checks.
>
> It's clearly better than set_fs(), but the way I prefer to convert the
> code is to avoid both and instead move compat handlers next to
> the native code, and splitting out the common code between native
> and compat mode into a helper that takes a regular kernel pointer.
>
> I think that's what both Al has done in the past on compat_ioctl()
> and select() and what Christoph does in his latest series, but
> it seems worth pointing out for others that decide to help out here.
Folks, reducing the amount of places where we play with set_fs() is certainly
a good thing. Getting rid of them completely is something entirely different;
I have tried to plot out patch series in this direction many times during the
last 5 years or so, but it's not going to be easy. Tomorrow I can start
posting my notes in that direction (and there are tons of those, unfortunately
mixed with git grep results, highly unprintable personal comments, etc.);
just let me grab some sleep first...
BTW, slow userland access is not just due to extra checks; access_ok(),
in particular, is pretty much noise. The real PITA comes from the things
like STAC/CLAC on recent x86. Or hardware overhead of cross-address-space
block copy insn (e.g. on s390, where it's optimized for multi-cacheline
blocks). Or things like uml, where it's a matter of walking the page
tables for each sodding __get_user(). It's not always just a matter of
address space limit...
next prev parent reply other threads:[~2017-05-10 8:09 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-28 15:32 [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode Thomas Garnier
2017-04-28 15:32 ` [PATCH v9 2/4] x86/syscalls: Optimize address limit check Thomas Garnier
2017-04-28 15:32 ` [PATCH v9 3/4] arm/syscalls: " Thomas Garnier
2017-04-28 15:32 ` [PATCH v9 4/4] arm64/syscalls: " Thomas Garnier
2017-05-05 22:18 ` [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode Thomas Garnier
2017-05-08 7:33 ` Ingo Molnar
2017-05-08 7:52 ` Ingo Molnar
2017-05-08 15:22 ` [kernel-hardening] " Daniel Micay
2017-05-08 15:26 ` Kees Cook
2017-05-08 19:51 ` Thomas Garnier
2017-05-09 6:56 ` Ingo Molnar
2017-05-09 11:10 ` Greg KH
2017-05-09 14:29 ` Thomas Garnier
2017-05-11 23:17 ` Thomas Garnier
2017-05-11 23:44 ` Linus Torvalds
2017-05-12 5:28 ` Martin Schwidefsky
2017-05-12 5:34 ` Kees Cook
2017-05-12 5:54 ` Martin Schwidefsky
2017-05-12 19:01 ` Kees Cook
2017-05-12 19:08 ` Russell King - ARM Linux
2017-05-12 19:08 ` Linus Torvalds
2017-05-12 19:30 ` Kees Cook
2017-05-12 20:21 ` Russell King - ARM Linux
2017-05-12 20:30 ` Peter Zijlstra
2017-05-12 20:45 ` Russell King - ARM Linux
2017-05-12 21:00 ` Kees Cook
2017-05-12 21:04 ` Kees Cook
2017-05-13 7:21 ` Christoph Hellwig
2017-05-12 21:06 ` Al Viro
2017-05-12 21:16 ` Daniel Micay
2017-05-12 21:17 ` Kees Cook
2017-05-12 21:23 ` Daniel Micay
2017-05-12 21:41 ` Al Viro
2017-05-12 21:47 ` Rik van Riel
2017-05-12 22:57 ` Al Viro
2017-05-12 21:50 ` Kees Cook
2017-05-12 6:57 ` Ingo Molnar
2017-05-12 6:13 ` Andy Lutomirski
2017-05-12 6:58 ` Ingo Molnar
2017-05-12 17:05 ` Thomas Garnier
2017-05-09 16:30 ` Kees Cook
2017-05-08 12:46 ` Greg KH
2017-05-09 6:45 ` Ingo Molnar
2017-05-09 8:56 ` Christoph Hellwig
2017-05-09 13:00 ` Andy Lutomirski
2017-05-09 13:02 ` Christoph Hellwig
2017-05-09 16:03 ` Christoph Hellwig
2017-05-09 16:50 ` Kees Cook
2017-05-09 22:52 ` Andy Lutomirski
2017-05-09 23:31 ` Kees Cook
2017-05-10 1:59 ` Andy Lutomirski
2017-05-10 7:15 ` Christoph Hellwig
2017-05-11 11:22 ` Borislav Petkov
2017-05-10 6:46 ` Christoph Hellwig
2017-05-10 2:11 ` Al Viro
2017-05-10 2:45 ` Al Viro
2017-05-10 3:12 ` Al Viro
2017-05-10 3:21 ` Al Viro
2017-05-10 3:39 ` Al Viro
2017-05-10 6:54 ` Christoph Hellwig
2017-05-10 6:53 ` Christoph Hellwig
2017-05-10 7:27 ` Al Viro
2017-05-10 7:35 ` Christoph Hellwig
2017-05-10 6:49 ` Christoph Hellwig
2017-05-10 7:28 ` Arnd Bergmann
2017-05-10 7:35 ` Christoph Hellwig
2017-05-09 16:05 ` Brian Gerst
2017-05-10 7:37 ` Arnd Bergmann
2017-05-10 8:08 ` Al Viro [this message]
2017-05-10 8:14 ` Christoph Hellwig
2017-05-11 0:18 ` Andy Lutomirski
2017-05-12 7:00 ` Ingo Molnar
2017-05-12 7:15 ` Al Viro
2017-05-12 7:35 ` Christoph Hellwig
2017-05-12 7:43 ` Arnd Bergmann
2017-05-12 8:11 ` Christoph Hellwig
2017-05-12 8:16 ` Al Viro
2017-05-12 8:11 ` Al Viro
2017-05-12 8:20 ` Arnd Bergmann
2017-05-12 23:20 ` Andy Lutomirski
2017-05-08 13:09 ` Kees Cook
2017-05-08 14:02 ` Ingo Molnar
2017-05-08 14:06 ` Jann Horn
2017-05-08 20:48 ` Al Viro
2017-05-12 23:15 ` Andy Lutomirski
2017-05-08 15:24 ` Kees Cook
2017-05-09 6:34 ` Ingo Molnar
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