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]: b1e42e09ac
[3]: 4c1b2066eb
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200406221604.18547-1-luke.r.nels@gmail.com
This patch factors out code that can be used by both the RV64 and RV32
BPF JITs to a common bpf_jit.h and bpf_jit_core.c.
Move struct definitions and macro-like functions to header. Rename
rv_sb_insn/rv_uj_insn to rv_b_insn/rv_j_insn to match the RISC-V
specification.
Move reusable functions emit_body() and bpf_int_jit_compile() to
bpf_jit_core.c with minor simplifications. Rename emit_insn() and
build_{prologue,epilogue}() to be prefixed with "bpf_jit_" as they are
no longer static.
Rename bpf_jit_comp.c to bpf_jit_comp64.c to be more explicit.
Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Link: https://lore.kernel.org/bpf/20200305050207.4159-2-luke.r.nels@gmail.com
Luke Nelson