From: Markos Chandras <Markos.Chandras@imgtec.com>
To: David Laight <David.Laight@ACULAB.COM>,
"linux-mips@linux-mips.org" <linux-mips@linux-mips.org>
Cc: "David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <dborkman@redhat.com>,
Alexei Starovoitov <ast@plumgrid.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH 14/17] MIPS: bpf: Prevent kernel fall over for >=32bit shifts
Date: Mon, 23 Jun 2014 12:06:15 +0100 [thread overview]
Message-ID: <53A80A27.5090503@imgtec.com> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1726096C@AcuExch.aculab.com>
On 06/23/2014 10:44 AM, David Laight wrote:
> From: Markos Chandras
>> Remove BUG_ON() if the shift immediate is >=32 to avoid
>> kernel crashes due to malicious user input. Since the micro-assembler
>> will not allow an immediate greater or equal to 32, we will use the
>> maximum value which is 31. This will do the correct thing on either 32-
>> or 64-bit cores since no 64-bit instructions are being used in JIT.
>
> I'm not sure that bounding the shift to 31 bits 'is the correct thing'.
> I'd have thought that emulating the large shift or masking the shift
> to 5 bits are equally 'correct'.
>
> ...
Hi David,
Since we use 32-bit registers (or rather, we ignore the top 32bits on
MIPS64), shifting >= 32 will always result to 0.
Alexei suggested [1] to allow large shifts and emulate them, so this
patch aims to do that by treating >=32 shift values as 31. Please tell
me if I got this wrong.
[1] http://www.linux-mips.org/archives/linux-mips/2014-06/msg00212.html
--
markos
next prev parent reply other threads:[~2014-06-23 11:06 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-23 9:38 [PATCH 00/17] Misc MIPS/BPF fixes for 3.16 Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 01/17] MIPS: uasm: Add s3s1s2 instruction builder Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 02/17] MIPS: uasm: Add slt uasm instruction Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 03/17] MIPS: mm: uasm: Fix lh micro-assembler instruction Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 04/17] MIPS: bpf: Use the LO register to get division's quotient Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 05/17] MIPS: bpf: Return error code if the offset is a negative number Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 22:09 ` Alexei Starovoitov
2014-06-25 8:12 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 06/17] MIPS: bpf: Use 'andi' instead of 'and' for the VLAN cases Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 07/17] MIPS: bpf: Add SEEN_SKB to flags when looking for the PKT_TYPE Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 08/17] MIPS: bpf: Fix branch conditional for BPF_J{GT/GE} cases Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 09/17] MIPS: bpf: Use correct mask for VLAN_TAG case Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 10/17] MIPS: bpf: Fix return values for VLAN_TAG_PRESENT case Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 11/17] MIPS: bpf: Use pr_debug instead of pr_warn for unhandled opcodes Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 12/17] MIPS: bpf: Fix is_range() semantics Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 13/17] MIPS: bpf: Drop update_on_xread and always initialize the X register Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 14/17] MIPS: bpf: Prevent kernel fall over for >=32bit shifts Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:44 ` David Laight
2014-06-23 11:06 ` Markos Chandras [this message]
2014-06-23 11:08 ` David Laight
2014-06-23 11:39 ` Markos Chandras
2014-06-25 8:37 ` [PATCH v2 " Markos Chandras
2014-06-25 8:37 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 15/17] MIPS: bpf: Fix PKT_TYPE case for big-endian cores Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 9:38 ` [PATCH 16/17] MIPS: bpf: Use 32 or 64-bit load instruction to load an address to register Markos Chandras
2014-06-23 9:38 ` Markos Chandras
2014-06-23 20:24 ` Paul Burton
2014-06-23 20:24 ` Paul Burton
2014-06-25 8:18 ` Markos Chandras
2014-06-25 8:18 ` Markos Chandras
2014-06-25 8:39 ` [PATCH v2 " Markos Chandras
2014-06-25 8:39 ` Markos Chandras
2014-06-25 14:28 ` Alexei Starovoitov
2014-06-23 9:39 ` [PATCH 17/17] MIPS: bpf: Fix stack space allocation for BPF memwords on MIPS64 Markos Chandras
2014-06-23 9:39 ` Markos Chandras
2014-06-23 19:49 ` [PATCH 00/17] Misc MIPS/BPF fixes for 3.16 David Miller
2014-06-25 8:12 ` Markos Chandras
2014-06-25 8:12 ` Markos Chandras
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