From: Dan Williams <dan.j.williams@intel.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
Netdev <netdev@vger.kernel.org>,
Greg KH <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"David S. Miller" <davem@davemloft.net>,
Elena Reshetova <elena.reshetova@intel.com>,
Alan Cox <alan@linux.intel.com>
Subject: Re: [PATCH 16/18] net: mpls: prevent bounds-check bypass via speculative execution
Date: Tue, 9 Jan 2018 18:22:09 -0800 [thread overview]
Message-ID: <CAPcyv4h1Uvke8d8JThHMLuci5HMKLf3hHgtkpcch1QSpq35M+Q@mail.gmail.com> (raw)
In-Reply-To: <20180110015713.im4atka6sahz7ucx@ast-mbp>
On Tue, Jan 9, 2018 at 5:57 PM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Tue, Jan 09, 2018 at 04:48:24PM -0800, Dan Williams wrote:
>>
>> #define __nospec_array_ptr(base, idx, sz) \
>> ({ \
>> union { typeof(&base[0]) _ptr; unsigned long _bit; } __u; \
>> unsigned long _i = (idx); \
>> unsigned long _s = (sz); \
>> unsigned long _v = (long)(_i | _s - 1 - _i) \
>> >> BITS_PER_LONG - 1; \
>> unsigned long _mask = _v * ~0UL; \
>> OPTIMIZER_HIDE_VAR(_mask); \
>> __u._ptr = &base[_i & _mask]; \
>> __u._bit &= _mask; \
>> __u._ptr; \
>> })
>
> _v * ~0UL doesn't seem right and non intuitive.
> What's wrong with:
> unsigned long _mask = ~(long)(_i | _s - 1 - _i) >> BITS_PER_LONG - 1;
Yeah, I noticed it was ok immediately after I sent that.
> and why OPTIMIZER_HIDE_VAR ?
It was in Linus' original. but that was when it had the ternary
conditional, I'll drop it. It does not change the generated assembly.
> Could you remove '&' ?
Yes, that should be __u.ptr = base + (i & _mask)
> since in doesn't work for:
> struct {
> int fd[4];
> ...
> } *fdt;
> it cannot be used as array_acces(fdt->fd, ...);
>
> Could you please drop nospec_ prefix since it is misleading ?
When you came up with that tweak you noted:
"The following:
[..]
is generic and no speculative flows."
> This macro doesn't prevent speculation.
It masks dangerous speculation. At least, I read nospec as "No
Spectre" and it is a prefix used in the Spectre-v2 patches.
I also want to include the option, with a static branch, to switch it
to the hard "no speculation" version with an ifence if worse comes to
worse and we find a compiler / cpu where it doesn't work. The default
will be the fast and practical implementation.
> I think array_access() was the best name so far.
For other usages I need the pointer to the array element, also
array_access() by itself is unsuitable for __fcheck_files because we
still need rcu_dereference_raw() on the element de-reference. So, I
think it's better to get a sanitized array element pointer which can
be used with rcu, READ_ONCE(), etc... directly rather than try to do
the access in the same macro.
next prev parent reply other threads:[~2018-01-10 2:22 UTC|newest]
Thread overview: 161+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-06 1:09 [PATCH 00/18] prevent bounds-check bypass via speculative execution Dan Williams
2018-01-06 1:09 ` [PATCH 01/18] asm-generic/barrier: add generic nospec helpers Dan Williams
2018-01-06 2:55 ` Linus Torvalds
2018-01-06 5:23 ` Dan Williams
2018-01-06 17:08 ` Mark Rutland
2018-01-06 1:10 ` [PATCH 02/18] Documentation: document " Dan Williams
2018-01-08 16:29 ` Jonathan Corbet
2018-01-08 17:09 ` Mark Rutland
2018-01-08 21:19 ` Jonathan Corbet
2018-01-06 1:10 ` [PATCH 03/18] arm64: implement nospec_ptr() Dan Williams
2018-01-06 1:10 ` [PATCH 04/18] arm: " Dan Williams
2018-01-10 2:04 ` Laura Abbott
2018-01-10 7:40 ` Hanjun Guo
2018-01-10 17:24 ` Laura Abbott
2018-01-06 1:10 ` [PATCH 05/18] x86: implement nospec_barrier() Dan Williams
2018-01-06 1:10 ` [PATCH 06/18] x86, barrier: stop speculation for failed access_ok Dan Williams
2018-01-06 2:52 ` Linus Torvalds
2018-01-06 3:09 ` Linus Torvalds
2018-01-06 23:31 ` Dan Williams
2018-01-07 1:20 ` Linus Torvalds
2018-01-08 21:09 ` Dan Williams
2018-01-08 23:44 ` Linus Torvalds
2018-01-08 23:53 ` Dan Williams
2018-01-06 5:47 ` Dan Williams
2018-01-06 12:32 ` Alan Cox
2018-01-06 17:56 ` Linus Torvalds
2018-01-06 18:13 ` Alexei Starovoitov
2018-01-06 18:29 ` Dan Williams
2018-01-06 18:39 ` Alexei Starovoitov
2018-01-06 18:54 ` Dan Williams
2018-01-06 19:25 ` Alexei Starovoitov
2018-01-06 19:36 ` Dan Williams
2018-01-06 19:41 ` Thomas Gleixner
2018-01-08 10:02 ` Andrea Arcangeli
2018-01-06 18:38 ` Alan Cox
2018-01-06 18:51 ` Alexei Starovoitov
2018-01-06 19:55 ` Alan Cox
2018-01-06 20:09 ` Alexei Starovoitov
2018-01-06 20:22 ` Alan Cox
2018-01-06 21:17 ` Alexei Starovoitov
2018-01-06 21:21 ` Thomas Gleixner
2018-01-06 23:05 ` Alan Cox
2018-01-07 3:38 ` Alexei Starovoitov
2018-01-07 6:33 ` Willy Tarreau
2018-01-07 19:47 ` Linus Torvalds
2018-01-07 20:12 ` Willy Tarreau
2018-01-07 20:17 ` Linus Torvalds
2018-01-07 20:56 ` Thomas Gleixner
2018-01-08 2:23 ` David Miller
2018-01-08 7:38 ` Greg KH
2018-01-07 22:15 ` Willy Tarreau
2018-01-07 20:15 ` Dan Williams
2018-01-08 2:24 ` Alexei Starovoitov
2018-01-08 9:51 ` Peter Zijlstra
2018-01-08 18:21 ` Ingo Molnar
2018-01-08 12:00 ` David Laight
2018-01-08 12:12 ` Alan Cox
2018-01-08 12:33 ` David Laight
2018-01-07 10:08 ` Thomas Gleixner
2018-01-08 2:09 ` Alexei Starovoitov
2018-01-07 13:59 ` Alan Cox
2018-01-08 2:57 ` Alexei Starovoitov
2018-01-08 9:57 ` Peter Zijlstra
2018-01-06 20:42 ` Willy Tarreau
2018-01-07 1:36 ` David Miller
2018-01-07 17:19 ` James Bottomley
2018-01-07 18:31 ` Thomas Gleixner
2018-01-08 2:04 ` David Miller
2018-01-07 19:24 ` Alan Cox
2018-01-09 21:41 ` Josh Poimboeuf
2018-01-09 21:47 ` Dan Williams
2018-01-09 21:49 ` Josh Poimboeuf
2018-01-09 21:59 ` Dan Williams
2018-01-09 22:23 ` Josh Poimboeuf
2018-01-09 22:35 ` Dan Williams
2018-01-06 1:10 ` [PATCH 07/18] [media] uvcvideo: prevent bounds-check bypass via speculative execution Dan Williams
2018-01-06 9:09 ` Greg KH
2018-01-06 9:40 ` Greg KH
2018-01-06 17:41 ` Dan Williams
2018-01-07 9:09 ` Greg KH
2018-01-07 19:37 ` Dan Williams
2018-01-09 8:40 ` Laurent Pinchart
2018-01-09 10:04 ` Greg KH
2018-01-09 14:26 ` Laurent Pinchart
2018-01-09 14:47 ` Greg KH
2018-01-08 11:23 ` Laurent Pinchart
2018-01-09 2:11 ` Dan Williams
2018-01-06 1:10 ` [PATCH 08/18] carl9170: " Dan Williams
2018-01-06 10:01 ` Sergei Shtylyov
2018-01-06 14:23 ` Christian Lamparter
2018-01-06 15:06 ` Alan Cox
2018-01-06 16:38 ` Christian Lamparter
2018-01-06 16:34 ` Dan Williams
2018-01-06 1:10 ` [PATCH 09/18] p54: " Dan Williams
2018-01-06 10:01 ` Sergei Shtylyov
2018-01-06 1:10 ` [PATCH 10/18] qla2xxx: " Dan Williams
2018-01-06 9:03 ` Greg KH
2018-01-06 9:42 ` Greg KH
2018-01-11 22:15 ` Dan Williams
2018-01-12 7:27 ` Greg KH
2018-01-12 15:25 ` James Bottomley
2018-01-06 1:10 ` [PATCH 11/18] cw1200: " Dan Williams
2018-01-06 1:10 ` [PATCH 12/18] Thermal/int340x: " Dan Williams
2018-01-06 1:53 ` Srinivas Pandruvada
2018-01-06 1:57 ` Dan Williams
2018-01-06 17:24 ` Srinivas Pandruvada
2018-01-06 10:03 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 13/18] ipv6: " Dan Williams
2018-01-06 10:04 ` Sergei Shtylyov
2018-01-06 14:48 ` Stephen Hemminger
2018-01-06 18:05 ` Dan Williams
2018-01-06 1:11 ` [PATCH 14/18] ipv4: " Dan Williams
2018-01-06 9:00 ` Greg KH
2018-01-06 9:01 ` Greg KH
2018-01-06 12:23 ` Alan Cox
2018-01-06 15:14 ` Greg KH
2018-01-06 16:29 ` Dan Williams
2018-01-06 18:10 ` Dan Williams
2018-01-06 10:04 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 15/18] vfs, fdtable: " Dan Williams
2018-01-06 10:05 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 16/18] net: mpls: " Dan Williams
2018-01-06 10:06 ` Sergei Shtylyov
2018-01-09 3:11 ` Eric W. Biederman
2018-01-09 3:42 ` Dan Williams
2018-01-09 4:13 ` Linus Torvalds
2018-01-09 4:21 ` Linus Torvalds
2018-01-10 0:48 ` Dan Williams
2018-01-10 1:33 ` Dan Williams
2018-01-10 1:57 ` Alexei Starovoitov
2018-01-10 2:22 ` Dan Williams [this message]
2018-01-10 3:07 ` Alexei Starovoitov
2018-01-10 3:27 ` Linus Torvalds
2018-01-09 16:17 ` Eric W. Biederman
2018-01-09 18:01 ` Dan Williams
2018-01-10 0:54 ` Eric W. Biederman
2018-01-10 1:31 ` Dan Williams
2018-01-06 1:11 ` [PATCH 17/18] udf: " Dan Williams
2018-01-08 10:20 ` Jan Kara
2018-01-06 1:11 ` [PATCH 18/18] userns: " Dan Williams
2018-01-06 2:22 ` [PATCH 00/18] " Eric W. Biederman
2018-01-06 6:30 ` Dan Williams
2018-01-08 10:08 ` Peter Zijlstra
2018-01-08 11:14 ` Laurent Pinchart
2018-01-08 11:43 ` Alan Cox
2018-01-08 11:55 ` Peter Zijlstra
2018-01-08 18:33 ` Ingo Molnar
2018-01-08 16:20 ` Bart Van Assche
2018-01-06 18:56 ` Florian Fainelli
2018-01-06 18:59 ` Arjan van de Ven
2018-01-06 19:37 ` Dan Williams
2018-01-06 20:07 ` Dan Williams
2018-01-08 4:49 ` Bart Van Assche
2018-01-08 13:33 ` Arjan van de Ven
2018-01-09 19:34 ` Jiri Kosina
2018-01-09 19:44 ` Dan Williams
2018-01-09 20:55 ` Josh Poimboeuf
2018-01-11 9:54 ` Jiri Kosina
2018-01-11 15:58 ` Dan Williams
2018-01-11 16:34 ` Daniel Borkmann
2018-01-13 11:33 ` QingFeng Hao
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