On Tue, 7 Apr 2020 at 00:16, Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx> wrote: > > The existing code in emit_call on RV64 checks that the PC-relative offset > to the function fits in 32 bits before calling emit_jump_and_link to emit > an auipc+jalr pair. However, this check is incorrect because offsets in > the range [2^31 - 2^11, 2^31 - 1] cannot be encoded using auipc+jalr on > RV64 (see discussion [1]). The RISC-V spec has recently been updated > to reflect this fact [2, 3]. > > This patch fixes the problem by moving the check on the offset into > emit_jump_and_link and modifying it to the correct range of encodable > offsets, which is [-2^31 - 2^11, 2^31 - 2^11). This also enforces the > check on the offset to other uses of emit_jump_and_link (e.g., BPF_JA) > as well. > > Currently, this bug is unlikely to be triggered, because the memory > region from which JITed images are allocated is close enough to kernel > text for the offsets to not become too large; and because the bounds on > BPF program size are small enough. This patch prevents this problem from > becoming an issue if either of these change. > > [1]: https://groups.google.com/a/groups.riscv.org/forum/#!topic/isa-dev/bwWFhBnnZFQ > [2]: https://github.com/riscv/riscv-isa-manual/commit/b1e42e09ac55116dbf9de5e4fb326a5a90e4a993 > [3]: https://github.com/riscv/riscv-isa-manual/commit/4c1b2066ebd2965a422e41eb262d0a208a7fea07 > Wow! Interesting! Thanks for fixing this! Too late to Ack, but still: Acked-by: Björn Töpel <bjorn.topel@xxxxxxxxx> > Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx> > --- > arch/riscv/net/bpf_jit_comp64.c | 49 +++++++++++++++++++++------------ > 1 file changed, 32 insertions(+), 17 deletions(-) > > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c > index cc1985d8750a..d208a9fd6c52 100644 > --- a/arch/riscv/net/bpf_jit_comp64.c > +++ b/arch/riscv/net/bpf_jit_comp64.c > @@ -110,6 +110,16 @@ static bool is_32b_int(s64 val) > return -(1L << 31) <= val && val < (1L << 31); > } > > +static bool in_auipc_jalr_range(s64 val) > +{ > + /* > + * auipc+jalr can reach any signed PC-relative offset in the range > + * [-2^31 - 2^11, 2^31 - 2^11). > + */ > + return (-(1L << 31) - (1L << 11)) <= val && > + val < ((1L << 31) - (1L << 11)); > +} > + > static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx) > { > /* Note that the immediate from the add is sign-extended, > @@ -380,20 +390,24 @@ static void emit_sext_32_rd(u8 *rd, struct rv_jit_context *ctx) > *rd = RV_REG_T2; > } > > -static void emit_jump_and_link(u8 rd, s64 rvoff, bool force_jalr, > - struct rv_jit_context *ctx) > +static int emit_jump_and_link(u8 rd, s64 rvoff, bool force_jalr, > + struct rv_jit_context *ctx) > { > s64 upper, lower; > > if (rvoff && is_21b_int(rvoff) && !force_jalr) { > emit(rv_jal(rd, rvoff >> 1), ctx); > - return; > + return 0; > + } else if (in_auipc_jalr_range(rvoff)) { > + upper = (rvoff + (1 << 11)) >> 12; > + lower = rvoff & 0xfff; > + emit(rv_auipc(RV_REG_T1, upper), ctx); > + emit(rv_jalr(rd, RV_REG_T1, lower), ctx); > + return 0; > } > > - upper = (rvoff + (1 << 11)) >> 12; > - lower = rvoff & 0xfff; > - emit(rv_auipc(RV_REG_T1, upper), ctx); > - emit(rv_jalr(rd, RV_REG_T1, lower), ctx); > + pr_err("bpf-jit: target offset 0x%llx is out of range\n", rvoff); > + return -ERANGE; > } > > static bool is_signed_bpf_cond(u8 cond) > @@ -407,18 +421,16 @@ static int emit_call(bool fixed, u64 addr, struct rv_jit_context *ctx) > s64 off = 0; > u64 ip; > u8 rd; > + int ret; > > if (addr && ctx->insns) { > ip = (u64)(long)(ctx->insns + ctx->ninsns); > off = addr - ip; > - if (!is_32b_int(off)) { > - pr_err("bpf-jit: target call addr %pK is out of range\n", > - (void *)addr); > - return -ERANGE; > - } > } > > - emit_jump_and_link(RV_REG_RA, off, !fixed, ctx); > + ret = emit_jump_and_link(RV_REG_RA, off, !fixed, ctx); > + if (ret) > + return ret; > rd = bpf_to_rv_reg(BPF_REG_0, ctx); > emit(rv_addi(rd, RV_REG_A0, 0), ctx); > return 0; > @@ -429,7 +441,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, > { > bool is64 = BPF_CLASS(insn->code) == BPF_ALU64 || > BPF_CLASS(insn->code) == BPF_JMP; > - int s, e, rvoff, i = insn - ctx->prog->insnsi; > + int s, e, rvoff, ret, i = insn - ctx->prog->insnsi; > struct bpf_prog_aux *aux = ctx->prog->aux; > u8 rd = -1, rs = -1, code = insn->code; > s16 off = insn->off; > @@ -699,7 +711,9 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, > /* JUMP off */ > case BPF_JMP | BPF_JA: > rvoff = rv_offset(i, off, ctx); > - emit_jump_and_link(RV_REG_ZERO, rvoff, false, ctx); > + ret = emit_jump_and_link(RV_REG_ZERO, rvoff, false, ctx); > + if (ret) > + return ret; > break; > > /* IF (dst COND src) JUMP off */ > @@ -801,7 +815,6 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, > case BPF_JMP | BPF_CALL: > { > bool fixed; > - int ret; > u64 addr; > > mark_call(ctx); > @@ -826,7 +839,9 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, > break; > > rvoff = epilogue_offset(ctx); > - emit_jump_and_link(RV_REG_ZERO, rvoff, false, ctx); > + ret = emit_jump_and_link(RV_REG_ZERO, rvoff, false, ctx); > + if (ret) > + return ret; > break; > > /* dst = imm64 */ > -- > 2.17.1 >
