From: Daniel Borkmann <daniel@iogearbox.net>
To: Dave Marchevsky <davemarchevsky@fb.com>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>, Yonghong Song <yhs@fb.com>,
netdev@vger.kernel.org
Subject: Re: [PATCH v3 bpf-next 2/7] bpf: add bpf_trace_vprintk helper
Date: Fri, 3 Sep 2021 10:00:00 +0200 [thread overview]
Message-ID: <1253feeb-9832-1a86-7eb2-5076698c4ca3@iogearbox.net> (raw)
In-Reply-To: <20210828052006.1313788-3-davemarchevsky@fb.com>
On 8/28/21 7:20 AM, Dave Marchevsky wrote:
> This helper is meant to be "bpf_trace_printk, but with proper vararg
> support". Follow bpf_snprintf's example and take a u64 pseudo-vararg
> array. Write to /sys/kernel/debug/tracing/trace_pipe using the same
> mechanism as bpf_trace_printk.
>
> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
lgtm, minor comments below:
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 9 ++++++
> kernel/bpf/core.c | 5 ++++
> kernel/bpf/helpers.c | 2 ++
> kernel/trace/bpf_trace.c | 52 +++++++++++++++++++++++++++++++++-
> tools/include/uapi/linux/bpf.h | 9 ++++++
> 6 files changed, 77 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index be8d57e6e78a..b6c45a6cbbba 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1088,6 +1088,7 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *f
> int bpf_prog_calc_tag(struct bpf_prog *fp);
>
> const struct bpf_func_proto *bpf_get_trace_printk_proto(void);
> +const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void);
>
> typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
> unsigned long off, unsigned long len);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 791f31dd0abe..f171d4d33136 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -4877,6 +4877,14 @@ union bpf_attr {
> * Get the struct pt_regs associated with **task**.
> * Return
> * A pointer to struct pt_regs.
> + *
> + * u64 bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data, u32 data_len)
s/u64/long/
> + * Description
> + * Behaves like **bpf_trace_printk**\ () helper, but takes an array of u64
nit: maybe for users it's more clear from description if you instead mention that data_len
needs to be multiple of 8 bytes? Or somehow mention the relation with data more clearly
resp. which shortcoming it addresses compared to bpf_trace_printk(), so developers can more
easily parse it.
> + * to format. Arguments are to be used as in **bpf_seq_printf**\ () helper.
> + * Return
> + * The number of bytes written to the buffer, or a negative error
> + * in case of failure.
> */
[...]
> default:
> return NULL;
> }
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10672ebc63b7..ea8358b0c748 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -398,7 +398,7 @@ static const struct bpf_func_proto bpf_trace_printk_proto = {
> .arg2_type = ARG_CONST_SIZE,
> };
>
> -const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
> +static void __set_printk_clr_event(void)
> {
> /*
> * This program might be calling bpf_trace_printk,
> @@ -410,10 +410,58 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
> */
> if (trace_set_clr_event("bpf_trace", "bpf_trace_printk", 1))
> pr_warn_ratelimited("could not enable bpf_trace_printk events");
> +}
>
> +const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
> +{
> + __set_printk_clr_event();
> return &bpf_trace_printk_proto;
> }
>
> +BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, data,
> + u32, data_len)
> +{
> + static char buf[BPF_TRACE_PRINTK_SIZE];
> + unsigned long flags;
> + int ret, num_args;
> + u32 *bin_args;
> +
> + if (data_len & 7 || data_len > MAX_BPRINTF_VARARGS * 8 ||
> + (data_len && !data))
> + return -EINVAL;
> + num_args = data_len / 8;
> +
> + ret = bpf_bprintf_prepare(fmt, fmt_size, data, &bin_args, num_args);
> + if (ret < 0)
> + return ret;
Given you have ARG_PTR_TO_MEM_OR_NULL for data, does this gracefully handle the
case where you pass in fmt string containing e.g. %ps but data being NULL? From
reading bpf_bprintf_prepare() looks like it does just fine, but might be nice
to explicitly add a tiny selftest case for it while you're at it.
> + raw_spin_lock_irqsave(&trace_printk_lock, flags);
> + ret = bstr_printf(buf, sizeof(buf), fmt, bin_args);
> +
> + trace_bpf_trace_printk(buf);
> + raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
> +
> + bpf_bprintf_cleanup();
> +
> + return ret;
> +}
Thanks,
Daniel
next prev parent reply other threads:[~2021-09-03 8:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-28 5:19 [PATCH v3 bpf-next 0/7] bpf: implement variadic printk helper Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 1/7] bpf: merge printk and seq_printf VARARG max macros Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 2/7] bpf: add bpf_trace_vprintk helper Dave Marchevsky
2021-08-30 23:35 ` Andrii Nakryiko
2021-09-03 8:00 ` Daniel Borkmann [this message]
2021-09-13 17:30 ` Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 3/7] libbpf: Modify bpf_printk to choose helper based on arg count Dave Marchevsky
2021-08-28 16:44 ` Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 4/7] libbpf: use static const fmt string in __bpf_printk Dave Marchevsky
2021-08-28 16:40 ` Dave Marchevsky
2021-08-29 16:57 ` Alexei Starovoitov
2021-08-31 0:36 ` Andrii Nakryiko
2021-08-31 0:37 ` Andrii Nakryiko
2021-08-28 5:20 ` [PATCH v3 bpf-next 5/7] bpftool: only probe trace_vprintk feature in 'full' mode Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 6/7] selftests/bpf: Migrate prog_tests/trace_printk CHECKs to ASSERTs Dave Marchevsky
2021-08-31 0:03 ` Andrii Nakryiko
2021-08-28 5:20 ` [PATCH v3 bpf-next 7/7] selftests/bpf: add trace_vprintk test prog Dave Marchevsky
2021-08-31 0:04 ` Andrii Nakryiko
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