linux-kernel - Re: [PATCH bpf v2] riscv, bpf: fix incorrect usage of BPF_TRAMP_F_ORIG

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Message-ID: <98266067-2bc2-4312-84d7-76966c3ebc1e@huawei.com>
Date: Sat, 20 Dec 2025 16:12:09 +0800
From: Pu Lehui <pulehui@...wei.com>
To: Menglong Dong <menglong.dong@...ux.dev>, Menglong Dong
	<menglong8.dong@...il.com>, <schwab@...ux-m68k.org>, <andrii@...nel.org>
CC: <ast@...nel.org>, <daniel@...earbox.net>, <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>,
	<puranjay@...nel.org>, <pjw@...nel.org>, <palmer@...belt.com>,
	<aou@...s.berkeley.edu>, <alex@...ti.fr>, <bpf@...r.kernel.org>,
	<linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf v2] riscv, bpf: fix incorrect usage of
 BPF_TRAMP_F_ORIG_STACK



On 2025/12/20 15:33, Menglong Dong wrote:
> On 2025/12/20 10:59, Pu Lehui wrote:
>>
>> On 2025/12/19 22:29, Menglong Dong 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>
>>> ---
>>> v2:
>>> - merge the code
>>> ---
>>>    arch/riscv/net/bpf_jit_comp64.c | 6 ++----
>>>    1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>>> index 5f9457e910e8..37888abee70c 100644
>>> --- a/arch/riscv/net/bpf_jit_comp64.c
>>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>>> @@ -1133,10 +1133,6 @@ 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)
>>
>> Oh, how did this weird flags get in here...
> 
> It's my fault. I wanted to use BPF_TRAMP_F_CALL_ORIG here, and
> a copy-paste mistake happen. They look a little similar :(
> 
>>
>>> -		orig_call += RV_FENTRY_NINSNS * 4;
>>> -
>>>    	if (flags & BPF_TRAMP_F_CALL_ORIG) {
>>>    		emit_imm(RV_REG_A0, ctx->insns ? (const s64)im : RV_MAX_COUNT_IMM, ctx);
>>>    		ret = emit_call((const u64)__bpf_tramp_enter, true, ctx);
>>> @@ -1171,6 +1167,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>>>    	}
>>>    
>>>    	if (flags & BPF_TRAMP_F_CALL_ORIG) {
>>> +		/* skip to actual body of traced function */
>>> +		orig_call += RV_FENTRY_NINSNS * 4;
>>
>>
>> LGTM, let's revert it.
>>
>> Reviewed-by: Pu Lehui <pulehui@...wei.com>
>>
>>>    		restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
>>>    		restore_stack_args(nr_arg_slots - RV_MAX_REG_ARGS, args_off, stk_arg_off, ctx);
>>>    		ret = emit_call((const u64)orig_call, true, ctx);
> 
> Andreas suggested that we remove the variable "orig_call" and use
> "func_addr + RV_FENTRY_NINSNS * 4" directly here. But I saw the V2
> is already applied. Hmm...I think it doesn't matter.

no warries. looks nice.

> 
> Thanks!
> Menglong Dong
> 
>>
>>
> 
> 
> 
> 
> 
>