| Message ID | 1557247291-9686-1-git-send-email-jiong.wang@netronome.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf] nfp: bpf: fix static check error through tightening shift amount adjustment | expand |
On Tue, May 7, 2019 at 9:42 AM Jiong Wang <jiong.wang@netronome.com> wrote: > > 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> Applied. Thanks
diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c index f272247..d4bf0e6 100644 --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c @@ -328,7 +328,18 @@ __emit_shf(struct nfp_prog *nfp_prog, u16 dst, enum alu_dst_ab dst_ab, return; } - if (sc == SHF_SC_L_SHF) + /* 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. + */ + if (sc == SHF_SC_L_SHF && shift) shift = 32 - shift; insn = OP_SHF_BASE |
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> --- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)