linux-kernel - Re: ebpf: BPF_ALU32 | BPF

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Message-ID: <xuny7e9aoskh.fsf@redhat.com>
Date:   Tue, 25 Jun 2019 13:41:34 +0300
From:   Yauheni Kaliuta <yauheni.kaliuta@...hat.com>
To:     Jiong Wang <jiong.wang@...ronome.com>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Jiri Benc <jbenc@...hat.com>, bpf@...r.kernel.org
Subject: Re: ebpf: BPF_ALU32 | BPF_ARSH on BE arches

Hi, Jiong!

>>>>> On Tue, 25 Jun 2019 11:20:07 +0100, Jiong Wang  wrote:

 > Yauheni Kaliuta writes:

 >> Hi!
 >> 
 >> Looks like the code:
 >> 
 >> ALU_ARSH_X:
 >> DST = (u64) (u32) ((*(s32 *) &DST) >> SRC);
 >> CONT;
 >> ALU_ARSH_K:
 >> DST = (u64) (u32) ((*(s32 *) &DST) >> IMM);
 >> CONT;
 >> 
 >> works incorrectly on BE arches since it must operate on lower
 >> parts of 64bit registers.
 >> 
 >> See failure of test_verifier test 'arsh32 on imm 2' (#23 on
 >> 5.2-rc6).

 > Ah, thanks for reporting this.

 > Should not taken the address directly, does the following fix resolved the
 > failure?

 >         ALU_ARSH_X:
 >                 DST = (u64) (u32) ((s32) DST) >> SRC);
 >                 CONT;
 >         ALU_ARSH_K:
 >                 DST = (u64) (u32) ((s32) DST) >> IMM);
 >                 CONT;

Yes, thanks (just add the missing braces).

-- 
WBR,
Yauheni Kaliuta