netdev - Re: [oss-drivers] [PATCH AUTOSEL 5.0 192/262] nfp: bpf: correct the behavior for shifts by zero

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Wed, 27 Mar 2019 11:14:52 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jiong Wang <jiong.wang@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, oss-drivers@...ronome.com
Subject: Re: [oss-drivers] [PATCH AUTOSEL 5.0 192/262] nfp: bpf: correct the
 behavior for shifts by zero

On Wed, 27 Mar 2019 14:00:47 -0400, Sasha Levin wrote:
> From: Jiong Wang <jiong.wang@...ronome.com>
> 
> [ Upstream commit db0a4b3b6b83a081a9ec309cc8178e5c9b4706a5 ]
> 
> Shifts by zero do nothing, and should be treated as nops.
> 
> Even though compiler is not supposed to generate such instructions and
> manual written assembly is unlikely to have them, but they are legal
> instructions and have defined behavior.
> 
> This patch correct existing shifts code-gen to make sure they do nothing
> when shift amount is zero except when the instruction is ALU32 for which
> high bits need to be cleared.
> 
> For shift amount bigger than type size, already, NFP JIT back-end errors
> out for immediate shift and only low 5 bits will be taken into account for
> indirect shift which is the same as x86.
> 
> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Nope.