From: Björn Töpel bjorn@rivosinc.com
[ Upstream commit c56fb2aab23505bb7160d06097c8de100b82b851 ]
In order to generate the prologue and epilogue, the BPF JIT needs to know which registers that are clobbered. Therefore, the during pre-final passes, the prologue is generated after the body of the program body-prologue-epilogue. Then, in the final pass, a proper prologue-body-epilogue JITted image is generated.
This scheme has worked most of the time. However, for some large programs with many jumps, e.g. the test_kmod.sh BPF selftest with hardening enabled (blinding constants), this has shown to be incorrect. For the final pass, when the proper prologue-body-epilogue is generated, the image has not converged. This will lead to that the final image will have incorrect jump offsets. The following is an excerpt from an incorrect image:
| ... | 3b8: 00c50663 beq a0,a2,3c4 <.text+0x3c4> | 3bc: 0020e317 auipc t1,0x20e | 3c0: 49630067 jalr zero,1174(t1) # 20e852 <.text+0x20e852> | ... | 20e84c: 8796 c.mv a5,t0 | 20e84e: 6422 c.ldsp s0,8(sp) # Epilogue start | 20e850: 6141 c.addi16sp sp,16 | 20e852: 853e c.mv a0,a5 # Incorrect jump target | 20e854: 8082 c.jr ra
The image has shrunk, and the epilogue offset is incorrect in the final pass.
Correct the problem by always generating proper prologue-body-epilogue outputs, which means that the first pass will only generate the body to track what registers that are touched.
Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G") Signed-off-by: Björn Töpel bjorn@rivosinc.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20230710074131.19596-1-bjorn@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/net/bpf_jit.h | 6 +++--- arch/riscv/net/bpf_jit_core.c | 19 +++++++++++++------ 2 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h index ab0cd6d10ccf3..ef336fe160044 100644 --- a/arch/riscv/net/bpf_jit.h +++ b/arch/riscv/net/bpf_jit.h @@ -69,7 +69,7 @@ struct rv_jit_context { struct bpf_prog *prog; u16 *insns; /* RV insns */ int ninsns; - int body_len; + int prologue_len; int epilogue_offset; int *offset; /* BPF to RV */ unsigned long flags; @@ -215,8 +215,8 @@ static inline int rv_offset(int insn, int off, struct rv_jit_context *ctx) int from, to;
off++; /* BPF branch is from PC+1, RV is from PC */ - from = (insn > 0) ? ctx->offset[insn - 1] : 0; - to = (insn + off > 0) ? ctx->offset[insn + off - 1] : 0; + from = (insn > 0) ? ctx->offset[insn - 1] : ctx->prologue_len; + to = (insn + off > 0) ? ctx->offset[insn + off - 1] : ctx->prologue_len; return ninsns_rvoff(to - from); }
diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c index ff644452b88db..b95c60f663d44 100644 --- a/arch/riscv/net/bpf_jit_core.c +++ b/arch/riscv/net/bpf_jit_core.c @@ -43,7 +43,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) { bool tmp_blinded = false, extra_pass = false; struct bpf_prog *tmp, *orig_prog = prog; - int pass = 0, prev_ninsns = 0, prologue_len, i; + int pass = 0, prev_ninsns = 0, i; struct rv_jit_data *jit_data; struct rv_jit_context *ctx; unsigned int image_size = 0; @@ -83,6 +83,12 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) prog = orig_prog; goto out_offset; } + + if (build_body(ctx, extra_pass, NULL)) { + prog = orig_prog; + goto out_offset; + } + for (i = 0; i < prog->len; i++) { prev_ninsns += 32; ctx->offset[i] = prev_ninsns; @@ -91,12 +97,15 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) for (i = 0; i < NR_JIT_ITERATIONS; i++) { pass++; ctx->ninsns = 0; + + bpf_jit_build_prologue(ctx); + ctx->prologue_len = ctx->ninsns; + if (build_body(ctx, extra_pass, ctx->offset)) { prog = orig_prog; goto out_offset; } - ctx->body_len = ctx->ninsns; - bpf_jit_build_prologue(ctx); + ctx->epilogue_offset = ctx->ninsns; bpf_jit_build_epilogue(ctx);
@@ -155,10 +164,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
if (!prog->is_func || extra_pass) { bpf_jit_binary_lock_ro(jit_data->header); - prologue_len = ctx->epilogue_offset - ctx->body_len; for (i = 0; i < prog->len; i++) - ctx->offset[i] = ninsns_rvoff(prologue_len + - ctx->offset[i]); + ctx->offset[i] = ninsns_rvoff(ctx->offset[i]); bpf_prog_fill_jited_linfo(prog, ctx->offset); out_offset: kfree(ctx->offset);