[PATCH bpf] riscv, bpf: fix incorrect usage of BPF_TRAMP_F_ORIG_STACK

[Andrii Nakryiko]

On Fri, Dec 19, 2025 at 6:43 AM Menglong Dong <menglong8.dong at gmail.com> wrote:
>
> The usage of BPF_TRAMP_F_ORIG_STACK in __arch_prepare_bpf_trampoline() is
> wrong, and it should be BPF_TRAMP_F_CALL_ORIG, which caused crash as
> Andreas reported:
>
>   Insufficient stack space to handle exception!
>   Task stack:     [0xff20000000010000..0xff20000000014000]
>   Overflow stack: [0xff600000ffdad070..0xff600000ffdae070]
>   CPU: 1 UID: 0 PID: 1 Comm: systemd Not tainted 6.18.0-rc5+ #15 PREEMPT(voluntary)
>   Hardware name: riscv-virtio qemu/qemu, BIOS 2025.10 10/01/2025
>   epc : copy_from_kernel_nofault+0xa/0x198
>    ra : bpf_probe_read_kernel+0x20/0x60
>   epc : ffffffff802b732a ra : ffffffff801e6070 sp : ff2000000000ffe0
>    gp : ffffffff82262ed0 tp : 0000000000000000 t0 : ffffffff80022320
>    t1 : ffffffff801e6056 t2 : 0000000000000000 s0 : ff20000000010040
>    s1 : 0000000000000008 a0 : ff20000000010050 a1 : ff60000083b3d320
>    a2 : 0000000000000008 a3 : 0000000000000097 a4 : 0000000000000000
>    a5 : 0000000000000000 a6 : 0000000000000021 a7 : 0000000000000003
>    s2 : ff20000000010050 s3 : ff6000008459fc18 s4 : ff60000083b3d340
>    s5 : ff20000000010060 s6 : 0000000000000000 s7 : ff20000000013aa8
>    s8 : 0000000000000000 s9 : 0000000000008000 s10: 000000000058dcb0
>    s11: 000000000058dca7 t3 : 000000006925116d t4 : ff6000008090f026
>    t5 : 00007fff9b0cbaa8 t6 : 0000000000000016
>   status: 0000000200000120 badaddr: 0000000000000000 cause: 8000000000000005
>   Kernel panic - not syncing: Kernel stack overflow
>   CPU: 1 UID: 0 PID: 1 Comm: systemd Not tainted 6.18.0-rc5+ #15 PREEMPT(voluntary)
>   Hardware name: riscv-virtio qemu/qemu, BIOS 2025.10 10/01/2025
>   Call Trace:
>   [<ffffffff8001a1f8>] dump_backtrace+0x28/0x38
>   [<ffffffff80002502>] show_stack+0x3a/0x50
>   [<ffffffff800122be>] dump_stack_lvl+0x56/0x80
>   [<ffffffff80012300>] dump_stack+0x18/0x22
>   [<ffffffff80002abe>] vpanic+0xf6/0x328
>   [<ffffffff80002d2e>] panic+0x3e/0x40
>   [<ffffffff80019ef0>] handle_bad_stack+0x98/0xa0
>   [<ffffffff801e6070>] bpf_probe_read_kernel+0x20/0x60
>
> Just fix it.
>
> Fixes: 47c9214dcbea ("bpf: fix the usage of BPF_TRAMP_F_SKIP_FRAME")
> Reported-by: Andreas Schwab <schwab at linux-m68k.org>
> Closes: https://lore.kernel.org/bpf/874ipnkfvt.fsf@igel.home/
> Signed-off-by: Menglong Dong <dongml2 at chinatelecom.cn>
> ---
>  arch/riscv/net/bpf_jit_comp64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 5f9457e910e8..09b70bf362d3 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -1134,7 +1134,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>         store_args(nr_arg_slots, args_off, ctx);
>
>         /* skip to actual body of traced function */
> -       if (flags & BPF_TRAMP_F_ORIG_STACK)
> +       if (flags & BPF_TRAMP_F_CALL_ORIG)
>                 orig_call += RV_FENTRY_NINSNS * 4;
>
>         if (flags & BPF_TRAMP_F_CALL_ORIG) {

move orig_call here, it's the same flags & BPF_TRAMP_F_CALL_ORIG check, no?

> --
> 2.52.0
>
>