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authorJiong Wang <jiong.wang@netronome.com>2019-05-07 19:41:30 +0300
committerAlexei Starovoitov <ast@kernel.org>2019-05-10 01:54:30 +0300
commit69e168ebdcfcb87ce7252d4857d570f99996fa27 (patch)
treed5c7fd423bf370b2ac75da54ce0cbe0e5f4eea60 /Documentation/bpf
parent07b619919d3d5401adc9bc6b79dcf12cc2c6d485 (diff)
downloadlinux-69e168ebdcfcb87ce7252d4857d570f99996fa27.tar.xz
nfp: bpf: fix static check error through tightening shift amount adjustment
NFP shift instruction has something special. If shift direction is left then shift amount of 1 to 31 is specified as 32 minus the amount to shift. But no need to do this for indirect shift which has shift amount be 0. Even after we do this subtraction, shift amount 0 will be turned into 32 which will eventually be encoded the same as 0 because only low 5 bits are encoded, but shift amount be 32 will fail the FIELD_PREP check done later on shift mask (0x1f), due to 32 is out of mask range. Such error has been observed when compiling nfp/bpf/jit.c using gcc 8.3 + O3. This issue has started when indirect shift support added after which the incoming shift amount to __emit_shf could be 0, therefore it is at that time shift amount adjustment inside __emit_shf should have been tightened. Fixes: 991f5b3651f6 ("nfp: bpf: support logic indirect shifts (BPF_[L|R]SH | BPF_X)") Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name> Reported-by: Pablo Cascón <pablo.cascon@netronome.com Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com> Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> Signed-off-by: Jiong Wang <jiong.wang@netronome.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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