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Message-ID: <830ab76b-ea2a-d522-73f9-b9392aecd0a4@iogearbox.net>
Date: Tue, 11 Jul 2023 22:03:47 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Palmer Dabbelt <palmer@...belt.com>, bjorn@...nel.org
Cc: ast@...nel.org, 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 7/11/23 7:50 PM, Palmer Dabbelt wrote:
> 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.
Sounds good, we applied it to bpf already.
Thanks,
Daniel
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