ebpf: BPF_ALU32 | BPF_ARSH on BE arches

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).

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Quoted 1 line · Jiong Wang

Quoted 11 lines · Yauheni Kaliuta

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;

Quoted 5 lines

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;