linux-kernel - Re: [PATCH bpf] riscv, bpf: fix incorrect usage of BPF_TRAMP_F_ORIG

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Message-ID: <CAEf4BzYzenxqVUty4RL15fVBR_bNLLgMAWHeMUyDkAeWWqbYug@mail.gmail.com>
Date: Fri, 19 Dec 2025 10:25:44 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, bjorn@...nel.org, 
	pulehui@...wei.com, puranjay@...nel.org, pjw@...nel.org, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, jiang.biao@...ux.dev, 
	bpf@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] riscv, bpf: fix incorrect usage of BPF_TRAMP_F_ORIG_STACK

On Fri, Dec 19, 2025 at 10:06 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Fri, Dec 19, 2025 at 6:43 AM Menglong Dong <menglong8.dong@...il.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@...ux-m68k.org>
> > Closes: https://lore.kernel.org/bpf/874ipnkfvt.fsf@igel.home/
> > Signed-off-by: Menglong Dong <dongml2@...natelecom.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?
>

ah, never mind, I see you send v2 adjusting this

> > --
> > 2.52.0
> >
> >