Re: [PATCH] arm64: bpf: fix div-by-zero case

[Shi, Yang]

On 11/4/2015 10:25 AM, Z Lim wrote:
> On Wed, Nov 4, 2015 at 10:21 AM, Shi, Yang <yang.shi@xxxxxxxxxx> wrote:
> > On 11/3/2015 11:04 PM, Xi Wang wrote:
> > > On Tue, Nov 3, 2015 at 10:56 PM, Zi Shen Lim <zlim.lnx@xxxxxxxxx> wrote:
> > > >           case BPF_ALU | BPF_DIV | BPF_X:
> > > >           case BPF_ALU64 | BPF_DIV | BPF_X:
> > > > +       {
> > > > +               const u8 r0 = bpf2a64[BPF_REG_0];
> > > > +
> > > > +               /* if (src == 0) return 0 */
> > > > +               jmp_offset = 3; /* skip ahead to else path */
> > > > +               check_imm19(jmp_offset);
> > > > +               emit(A64_CBNZ(is64, src, jmp_offset), ctx);
> > > > +               emit(A64_MOVZ(1, r0, 0, 0), ctx);
> > > > +               jmp_offset = epilogue_offset(ctx);
> > > > +               check_imm26(jmp_offset);
> > > > +               emit(A64_B(jmp_offset), ctx);
> > > > +               /* else */
> > > >                   emit(A64_UDIV(is64, dst, dst, src), ctx);
> > > >                   break;
> > > > +       }
> > > >           case BPF_ALU | BPF_MOD | BPF_X:
> > > >           case BPF_ALU64 | BPF_MOD | BPF_X:
> > >
> > >
> > > BPF_MOD might need the same fix.
>
> I'll post a fix for this case as well.
>
> > Agreed, and we may need add one more test cases in test_bpf module to cover
> > MOD?
>
> Let me know if you have a test case ready :)

Does the below change look like a valid test?

+               "MOD default X",
+               .u.insns = {
+                       /*
+                        * A = 0x42
+                        * A = A mod X ; this halt the filter execution 
if X is 0
+                        * ret 0x42
+                        */
+                       BPF_STMT(BPF_LD | BPF_IMM, 0x42),
+                       BPF_STMT(BPF_ALU | BPF_MOD | BPF_X, 0),
+                       BPF_STMT(BPF_RET | BPF_K, 0x42),
+               },
+               CLASSIC | FLAG_NO_DATA,
+               {},
+               { {0x1, 0x0 } },
+       },
+       {
+               "MOD default A",
+               .u.insns = {
+                       /*
+                        * A = A mod 1
+                        * ret A
+                        */
+                       BPF_STMT(BPF_ALU | BPF_MOD | BPF_K, 0x1),
+                       BPF_STMT(BPF_RET | BPF_A, 0x0),
+               },
+               CLASSIC | FLAG_NO_DATA,
+               {},
+               { {0x1, 0x0 } },
+       },

My test result with it:
test_bpf: #284 MOD default X jited:1 ret 66 != 0 FAIL (1 times)
test_bpf: #285 MOD default A jited:1 102 PASS

If it looks right, I will post a patch to add the test cases.

Thanks,
Yang

> > Yang
> >
> > > _______________________________________________
> > > linux-arm-kernel mailing list
> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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