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Date: Tue, 11 Jul 2023 10:50:26 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: bjorn@...nel.org
CC: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, bpf@...r.kernel.org,
netdev@...r.kernel.org, Bjorn Topel <bjorn@...osinc.com>, martin.lau@...ux.dev, song@...nel.org,
yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
haoluo@...gle.com, jolsa@...nel.org, pulehui@...wei.com, luke.r.nels@...il.com, xi.wang@...il.com,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, linux@...osinc.com
Subject: Re: [PATCH bpf] riscv, bpf: Fix inconsistent JIT image generation
On Mon, 10 Jul 2023 00:41:31 PDT (-0700), bjorn@...nel.org wrote:
> From: Björn Töpel <bjorn@...osinc.com>
>
> 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@...osinc.com>
> ---
> 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 bf9802a63061..2717f5490428 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 */
> int nexentries;
> @@ -216,8 +216,8 @@ 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 737baf8715da..7a26a3e1c73c 100644
> --- a/arch/riscv/net/bpf_jit_core.c
> +++ b/arch/riscv/net/bpf_jit_core.c
> @@ -44,7 +44,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> unsigned int prog_size = 0, extable_size = 0;
> 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;
>
> @@ -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);
>
> @@ -162,10 +171,8 @@ 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);
>
> base-commit: 496720b7cfb6574a8f6f4d434f23e3d1e6cfaeb9
Acked-by: Palmer Dabbelt <palmer@...osinc.com>
Reviewed-by: Palmer Dabbelt <palmer@...osinc.com>
I'm assuming this is aimed at the BPF tree, but LMK if you guys want me
to pick it up -- I've already got something for this week, so it's easy
on my end. I'm dropping it from my queue and patchwork for now, though.
Thanks for the fix!
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