On Mon, Sep 1, 2025 at 9:23 PM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
>
>
>
> On 2025/9/1 17:14, Hengqi Chen wrote:
> > On Mon, Sep 1, 2025 at 4:06 PM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
> >>
> >>
> >>
> >> On 2025/8/28 9:53, Pu Lehui wrote:
> >>>
> >>> On 2025/8/27 20:03, Hengqi Chen wrote:
> >>>> The ns_bpf_qdisc selftest triggers a kernel panic:
> >>>>
> >>>> Unable to handle kernel paging request at virtual address
> >>>> ffffffffa38dbf58
> >>>> Current test_progs pgtable: 4K pagesize, 57-bit VAs,
> >>>> pgdp=0x00000001109cc000
> >>>> [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401,
> >>>> pud=000000011fffd001, pmd=0000000000000000
> >>>> Oops [#1]
> >>>> Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1
> >>>> dm_mod drm drm_panel_orientation_quirks configfs backlight btrfs
> >>>> blake2b_generic xor lzo_compress zlib_deflate raid6_pq efivarfs [last
> >>>> unloaded: bpf_testmod(OE)]
> >>>> CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G W
> >>>> OE 6.17.0-rc1-g2465bb83e0b4 #1 NONE
> >>>> Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> >>>> Hardware name: Unknown Unknown Product/Unknown Product, BIOS
> >>>> 2024.01+dfsg-1ubuntu5.1 01/01/2024
> >>>> epc : __qdisc_run+0x82/0x6f0
> >>>> ra : __qdisc_run+0x6e/0x6f0
> >>>> epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
> >>>> gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
> >>>> t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
> >>>> s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
> >>>> a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
> >>>> a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
> >>>> s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
> >>>> s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
> >>>> s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
> >>>> s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
> >>>> t5 : 0000000000000000 t6 : ff60000093a6a8b6
> >>>> status: 0000000200000120 badaddr: ffffffffa38dbf58 cause:
> >>>> 000000000000000d
> >>>> [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
> >>>> [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
> >>>> [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
> >>>> [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
> >>>> [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
> >>>> [<ffffffff80d31446>] ip6_output+0x5e/0x178
> >>>> [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
> >>>> [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
> >>>> [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
> >>>> [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
> >>>> [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
> >>>> [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
> >>>> [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
> >>>> [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
> >>>> [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
> >>>> [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
> >>>> [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
> >>>> [<ffffffff80e69af2>] handle_exception+0x14a/0x156
> >>>> Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
> >>>> ---[ end trace 0000000000000000 ]---
> >>>>
> >>>> The bpf_fifo_dequeue prog returns a skb which is a pointer.
> >>>> The pointer is treated as a 32bit value and sign extend to
> >>>> 64bit in epilogue. This behavior is right for most bpf prog
> >>>> types but wrong for struct ops which requires RISC-V ABI.
> >>>
> >>> Hi Hengqi,
> >>>
> >>> Nice catch!
> >>>
> >>> Actually, I think commit 7112cd26e606c7ba51f9cc5c1905f06039f6f379 looks
> >>> a little bit wired and related to this issue. I guess I need some time
> >>> to recall this commit.
> >>
> >> Hi Hengqi,
> >>
> >> Sorry for late due to busy work. After some backtracking, I dismissed my
> >> doubts about commit 7112cd26e606.
> >>
> >>>
> >>> Thanks.
> >>>
> >>>>
> >>>> So let's sign extend struct ops return values according to
> >>>> the return value spec in function model.
> >>>>
> >>>> Fixes: 25ad10658dc1 ("riscv, bpf: Adapt bpf trampoline to optimized
> >>>> riscv ftrace framework")
> >>>> Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
> >>>> ---
> >>>> arch/riscv/net/bpf_jit_comp64.c | 33 +++++++++++++++++++++++++++++++++
> >>>> 1 file changed, 33 insertions(+)
> >>>>
> >>>> diff --git a/arch/riscv/net/bpf_jit_comp64.c
> >>>> b/arch/riscv/net/bpf_jit_comp64.c
> >>>> index 549c3063c7f1..11ca56320a3f 100644
> >>>> --- a/arch/riscv/net/bpf_jit_comp64.c
> >>>> +++ b/arch/riscv/net/bpf_jit_comp64.c
> >>>> @@ -954,6 +954,33 @@ static int invoke_bpf_prog(struct bpf_tramp_link
> >>>> *l, int args_off, int retval_of
> >>>> return ret;
> >>>> }
> >>>> +/*
> >>>> + * Sign-extend the register if necessary
> >>>> + */ >>>> +static int sign_extend(struct rv_jit_context *ctx, int r, u8 size)
>
> put `ctx` as last param would be more aligned with other function.
>
> >>>> +{
> >>>> + switch (size) {
> >>>> + case 1:
> >>>> + emit_slli(r, r, 56, ctx);
> >>>> + emit_srai(r, r, 56, ctx); >>>> + break;
> >>>> + case 2:
> >>>> + emit_slli(r, r, 48, ctx);
> >>>> + emit_srai(r, r, 48, ctx) >>>> + break;
> >>>> + case 4:
> >>>> + emit_addiw(r, r, 0, ctx);
>
> pls use emit_sextb/h/w() helper
>
> >>>> + break;
> >>>> + case 8:
> >>>> + break;
> >>>> + default:
> >>>> + pr_err("bpf-jit: invalid size %d for sign_extend\n", size);
> >>>> + return -EINVAL;
> >>>> + }
> >>>> +
> >>>> + return 0;
> >>>> +}
> >>
> >> We don't need to sign-ext when return value is 1 or 2 bytes. As for 4
> >
> > Could you please elaborate more on this ?
>
> Indeed, you pointed out my misunderstanding. According to riscv calling
> convention [0], for signed char and short, we need to do sign extension,
> but no need to do the same for unsigned. So for 1 or 2 bytes, we only
> need to do that for the signed.
>
> Link: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf [0]
>
Thanks, will do.
> > IIUC, addiw on 1 byte / 2 byte values is equivalent to zext them.
> >
> >> bytes, we have already do that in __build_epilogue. So we only need to
> >> take care of 8 bytes return value. And the real fix would be:
> >>
> >> diff --git a/arch/riscv/net/bpf_jit_comp64.c
> >> b/arch/riscv/net/bpf_jit_comp64.c
> >> index 2f7188e0340a..08cc641f8b7c 100644
> >> --- a/arch/riscv/net/bpf_jit_comp64.c
> >> +++ b/arch/riscv/net/bpf_jit_comp64.c
> >> @@ -1177,6 +1177,9 @@ static int __arch_prepare_bpf_trampoline(struct
> >> bpf_tramp_image *im,
> >> if (save_ret) {
> >> emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> >> emit_ld(regmap[BPF_REG_0], -(retval_off - 8),
> >> RV_REG_FP, ctx);
> >> + /* Do not truncate return value when it's 8 bytes */
> >> + if (is_struct_ops && m->ret_size == 8)
> >> + emit_mv(RV_REG_A0, regmap[BPF_REG_0], ctx);
> >> }
> >>
> >> emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
> >>
> >>>> +
> >>>> static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> >>>> const struct btf_func_model *m,
> >>>> struct bpf_tramp_links *tlinks,
> >>>> @@ -1177,6 +1204,12 @@ static int __arch_prepare_bpf_trampoline(struct
> >>>> bpf_tramp_image *im,
> >>>> if (save_ret) {
> >>>> emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
> >>>> emit_ld(regmap[BPF_REG_0], -(retval_off - 8), RV_REG_FP, ctx);
> >>>> + if (is_struct_ops) {
> >>>> + emit_mv(RV_REG_A0, regmap[BPF_REG_0], ctx);
>
> This could be omit by combining with the sign_extend insn like
> `sextb(rd, rs, ctx)`.
>
> >>>> + ret = sign_extend(ctx, RV_REG_A0, m->ret_size);
> >>>> + if (ret)
> >>>> + goto out;
> >>>> + }
> >>>> }
> >>>> emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
>
