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)
> >> +{
> >> + 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);
> >> + 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 ?
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);
> >> + 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);
