• Daniel Borkmann's avatar
    bpf, s390: fix jit branch offset related to ldimm64 · 731160f5
    Daniel Borkmann authored
    [ Upstream commit b0a0c256 ]
    
    While testing some other work that required JIT modifications, I
    run into test_bpf causing a hang when JIT enabled on s390. The
    problematic test case was the one from ddc665a4 (bpf, arm64:
    fix jit branch offset related to ldimm64), and turns out that we
    do have a similar issue on s390 as well. In bpf_jit_prog() we
    update next instruction address after returning from bpf_jit_insn()
    with an insn_count. bpf_jit_insn() returns either -1 in case of
    error (e.g. unsupported insn), 1 or 2. The latter is only the
    case for ldimm64 due to spanning 2 insns, however, next address
    is only set to i + 1 not taking actual insn_count into account,
    thus fix is to use insn_count instead of 1. bpf_jit_enable in
    mode 2 provides also disasm on s390:
    
    Before fix:
    
      000003ff800349b6: a7f40003   brc     15,3ff800349bc                 ; target
      000003ff800349ba: 0000               unknown
      000003ff800349bc: e3b0f0700024       stg     %r11,112(%r15)
      000003ff800349c2: e3e0f0880024       stg     %r14,136(%r15)
      000003ff800349c8: 0db0               basr    %r11,%r0
      000003ff800349ca: c0ef00000000       llilf   %r14,0
      000003ff800349d0: e320b0360004       lg      %r2,54(%r11)
      000003ff800349d6: e330b03e0004       lg      %r3,62(%r11)
      000003ff800349dc: ec23ffeda065       clgrj   %r2,%r3,10,3ff800349b6 ; jmp
      000003ff800349e2: e3e0b0460004       lg      %r14,70(%r11)
      000003ff800349e8: e3e0b04e0004       lg      %r14,78(%r11)
      000003ff800349ee: b904002e   lgr     %r2,%r14
      000003ff800349f2: e3b0f0700004       lg      %r11,112(%r15)
      000003ff800349f8: e3e0f0880004       lg      %r14,136(%r15)
      000003ff800349fe: 07fe               bcr     15,%r14
    
    After fix:
    
      000003ff80ef3db4: a7f40003   brc     15,3ff80ef3dba
      000003ff80ef3db8: 0000               unknown
      000003ff80ef3dba: e3b0f0700024       stg     %r11,112(%r15)
      000003ff80ef3dc0: e3e0f0880024       stg     %r14,136(%r15)
      000003ff80ef3dc6: 0db0               basr    %r11,%r0
      000003ff80ef3dc8: c0ef00000000       llilf   %r14,0
      000003ff80ef3dce: e320b0360004       lg      %r2,54(%r11)
      000003ff80ef3dd4: e330b03e0004       lg      %r3,62(%r11)
      000003ff80ef3dda: ec230006a065       clgrj   %r2,%r3,10,3ff80ef3de6 ; jmp
      000003ff80ef3de0: e3e0b0460004       lg      %r14,70(%r11)
      000003ff80ef3de6: e3e0b04e0004       lg      %r14,78(%r11)          ; target
      000003ff80ef3dec: b904002e   lgr     %r2,%r14
      000003ff80ef3df0: e3b0f0700004       lg      %r11,112(%r15)
      000003ff80ef3df6: e3e0f0880004       lg      %r14,136(%r15)
      000003ff80ef3dfc: 07fe               bcr     15,%r14
    
    test_bpf.ko suite runs fine after the fix.
    
    Fixes: 05462310 ("s390/bpf: Add s390x eBPF JIT compiler backend")
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Tested-by: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarSasha Levin <alexander.levin@verizon.com>
    731160f5
bpf_jit_comp.c 32.2 KB