"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> writes: > Since BPF constant blinding is performed after the verifier pass, there > are certain ALU32 instructions inserted which don't have a corresponding > zext instruction inserted after. This is causing a kernel oops on > powerpc and can be reproduced by running 'test_cgroup_storage' with > bpf_jit_harden=2. > > Fix this by emitting BPF_ZEXT during constant blinding if > prog->aux->verifier_zext is set. > > Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result") > Reported-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx> > --- > This approach (the location where zext is being introduced below, in > particular) works for powerpc, but I am not entirely sure if this is > sufficient for other architectures as well. This is broken on v5.3-rc4. Any comment on this? This is a regression in v5.3, which results in a kernel crash, it would be nice to get it fixed before the release please? cheers > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > index 8191a7db2777..d84146e6fd9e 100644 > --- a/kernel/bpf/core.c > +++ b/kernel/bpf/core.c > @@ -890,7 +890,8 @@ int bpf_jit_get_func_addr(const struct bpf_prog *prog, > > static int bpf_jit_blind_insn(const struct bpf_insn *from, > const struct bpf_insn *aux, > - struct bpf_insn *to_buff) > + struct bpf_insn *to_buff, > + bool emit_zext) > { > struct bpf_insn *to = to_buff; > u32 imm_rnd = get_random_int(); > @@ -939,6 +940,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, > *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); > *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); > *to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX); > + if (emit_zext) > + *to++ = BPF_ZEXT_REG(from->dst_reg); > break; > > case BPF_ALU64 | BPF_ADD | BPF_K: > @@ -992,6 +995,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, > off -= 2; > *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); > *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); > + if (emit_zext) { > + *to++ = BPF_ZEXT_REG(BPF_REG_AX); > + off--; > + } > *to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX, > off); > break; > @@ -1005,6 +1012,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, > case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */ > *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm); > *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); > + if (emit_zext) > + *to++ = BPF_ZEXT_REG(BPF_REG_AX); > *to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX); > break; > > @@ -1088,7 +1097,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog) > insn[1].code == 0) > memcpy(aux, insn, sizeof(aux)); > > - rewritten = bpf_jit_blind_insn(insn, aux, insn_buff); > + rewritten = bpf_jit_blind_insn(insn, aux, insn_buff, > + clone->aux->verifier_zext); > if (!rewritten) > continue; > > -- > 2.22.0