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Date: Tue, 11 Jul 2023 13:07:35 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: daniel@...earbox.net
CC: bjorn@...nel.org, 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 Tue, 11 Jul 2023 13:03:47 PDT (-0700), daniel@...earbox.net wrote:
> 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!
>
> Thanks,
> Daniel
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