Re: [PATCH bpf-next v3 3/6] bpf: fix the usage of BPF_TRAMP_F_SKIP_FRAME

Menglong Dong
2025-12-19T13:31:48Z

On 2025/12/19 20:27, Menglong Dong wrote:
> On 2025/12/19 19:41, Andreas Schwab wrote:
> > On Dez 19 2025, Menglong Dong wrote:
> >
> > > BPF_TRAMP_F_ORIG_STACK
> >
> > How can that ever be set?
>
> Oops, my bad! It should be BPF_TRAMP_F_CALL_ORIG here. I think
> it is some kind of copy-paste mistake. I'll send a fix for it.

I sent the following patch twice, but I didn't see it in the
mail list. I suspect there is something wrong with my gmail.

Hi, Alexei. Can you see my patch?

-->patch<--

From 5dbae5dcba3aa7fa10e506e9fd1a28a6802d9b00 Mon Sep 17 00:00:00 2001
From: Menglong Dong <dongml2@chinatelecom.cn>
Date: Fri, 19 Dec 2025 20:33:10 +0800
Subject: [PATCH RESEND bpf] riscv, bpf: fix incorrect usage of BPF_TRAMP_F_ORIG_STACK

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@linux-m68k.org>
Closes: https://lore.kernel.org/bpf/874ipnkfvt.fsf@igel.home/
Signed-off-by: Menglong Dong <dongml2@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) {
--
2.52.0

--<patch>--

>
> Thanks!
> Menglong Dong
>
> >
> > if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
> > return -ENOTSUPP;
> >
> >
>
>
>
>
>
>