From: Al Viro <viro@ZenIV.linux.org.uk>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
Kees Cook <keescook@chromium.org>,
kernel-hardening@lists.openwall.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
the arch/x86 maintainers <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Alan Cox <alan@linux.intel.com>
Subject: [kernel-hardening] Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths
Date: Wed, 17 Jan 2018 06:28:00 +0000 [thread overview]
Message-ID: <20180117062800.GU13338@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAPcyv4g94iysWqz64KNk=HDdx6+b2e0O-rRrnFZDqfNSR3Xrjg@mail.gmail.com>
On Tue, Jan 16, 2018 at 08:30:17PM -0800, Dan Williams wrote:
> On Tue, Jan 16, 2018 at 2:23 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > On Sat, Jan 13, 2018 at 11:33 AM, Linus Torvalds
> [..]
> > I'll respin this set along those lines, and drop the ifence bits.
>
> So now I'm not so sure. Yes, get_user_{1,2,4,8} can mask the pointer
> with the address limit result, but this doesn't work for the
> access_ok() + __get_user() case. We can either change the access_ok()
> calling convention to return a properly masked pointer to be used in
> subsequent calls to __get_user(), or go with lfence on every
> __get_user call. There seem to be several drivers that open code
> copy_from_user() with __get_user loops, so the 'fence every
> __get_user' approach might have noticeable overhead. On the other hand
> the access_ok conversion, while it could be scripted with coccinelle,
> is ~300 sites (VERIFY_READ), if you're concerned about having
> something small to merge for 4.15.
>
> I think the access_ok() conversion to return a speculation sanitized
> pointer or NULL is the way to go unless I'm missing something simpler.
> Other ideas?
What masked pointer? access_ok() exists for other architectures as well,
and the fewer callers remain outside of arch/*, the better.
Anything that open-codes copy_from_user() that way is *ALREADY* fucked if
it cares about the overhead - recent x86 boxen will have slowdown from
hell on stac()/clac() pairs. Anything like that on a hot path is already
deep in trouble and needs to be found and fixed. What drivers would those
be? We don't have that many __get_user() users left outside of arch/*
anymore...
next prev parent reply other threads:[~2018-01-17 6:28 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-13 18:17 [kernel-hardening] [PATCH v3 0/9] core, x86: prevent bounds-check bypass via speculative execution Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 1/9] Documentation: document array_ptr Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 2/9] arm64: implement ifence_array_ptr() Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 3/9] arm: " Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 4/9] x86: implement ifence() Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 5/9] x86: implement ifence_array_ptr() and array_ptr_mask() Dan Williams
2018-01-13 18:17 ` [kernel-hardening] [PATCH v3 6/9] asm/nospec: mask speculative execution flows Dan Williams
2018-01-13 18:18 ` [kernel-hardening] [PATCH v3 7/9] x86: introduce __uaccess_begin_nospec and ASM_IFENCE Dan Williams
2018-01-13 18:18 ` [kernel-hardening] [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths Dan Williams
2018-01-13 19:05 ` [kernel-hardening] " Linus Torvalds
2018-01-13 19:33 ` Linus Torvalds
2018-01-13 20:22 ` Eric W. Biederman
2018-01-16 22:23 ` Dan Williams
[not found] ` <CA+55aFxAFG5czVmCyhYMyHmXLNJ7pcXxWzusjZvLRh_qTGHj6Q@mail.gmail.com>
2018-01-16 22:41 ` Linus Torvalds
2018-01-17 14:17 ` Alan Cox
2018-01-17 18:52 ` Al Viro
2018-01-17 19:54 ` Dan Williams
2018-01-17 20:05 ` Al Viro
2018-01-17 20:14 ` Dan Williams
2018-01-18 3:06 ` [kernel-hardening] [RFC][PATCH] get rid of the use of set_fs() (by way of kernel_recvmsg()) in sunrpc Al Viro
2018-01-18 3:16 ` [kernel-hardening] " Linus Torvalds
2018-01-18 4:43 ` Al Viro
2018-01-18 16:29 ` Christoph Hellwig
2018-01-18 17:10 ` Al Viro
2018-01-18 19:31 ` Al Viro
2018-01-18 20:33 ` Al Viro
2018-01-19 3:27 ` Al Viro
2018-01-17 19:26 ` [kernel-hardening] Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths Linus Torvalds
2018-01-17 20:01 ` Eric Dumazet
2018-01-18 16:38 ` Christoph Hellwig
2018-01-18 16:49 ` Linus Torvalds
2018-01-18 18:12 ` Al Viro
2018-01-17 4:30 ` Dan Williams
2018-01-17 6:28 ` Al Viro [this message]
2018-01-17 6:50 ` Dan Williams
2018-01-17 10:07 ` [kernel-hardening] " David Laight
2018-01-17 18:12 ` [kernel-hardening] " Dan Williams
2018-01-17 19:16 ` Linus Torvalds
2018-01-13 18:18 ` [kernel-hardening] [PATCH v3 9/9] vfs, fdtable: prevent bounds-check bypass via speculative execution Dan Williams
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