Re: [PATCH bpf-next 4/4] bpf: export bpf_jit_current

[Daniel Borkmann <daniel@iogearbox.net>]

On 9/24/21 11:55 AM, Lorenz Bauer wrote:
> Expose bpf_jit_current as a read only value via sysctl.
> 
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
> ---
>   include/linux/filter.h     | 1 +
>   kernel/bpf/core.c          | 3 +--
>   net/core/sysctl_net_core.c | 7 +++++++
>   3 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index ef03ff34234d..b2143ad5ce00 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1052,6 +1052,7 @@ extern int bpf_jit_harden;
>   extern int bpf_jit_kallsyms;
>   extern long bpf_jit_limit;
>   extern long bpf_jit_limit_max;
> +extern atomic_long_t bpf_jit_current;
>   
>   typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);
>   
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index e844a2a4c99a..93f95e9ee8be 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -525,6 +525,7 @@ int bpf_jit_kallsyms __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
>   int bpf_jit_harden   __read_mostly;
>   long bpf_jit_limit   __read_mostly;
>   long bpf_jit_limit_max __read_mostly;
> +atomic_long_t bpf_jit_current __read_mostly;
>   
>   static void
>   bpf_prog_ksym_set_addr(struct bpf_prog *prog)
> @@ -800,8 +801,6 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
>   	return slot;
>   }
>   
> -static atomic_long_t bpf_jit_current;
> -
>   /* Can be overridden by an arch's JIT compiler if it has a custom,
>    * dedicated BPF backend memory area, or if neither of the two
>    * below apply.
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index 5f88526ad61c..674aac163b84 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -421,6 +421,13 @@ static struct ctl_table net_core_table[] = {
>   		.extra1		= &long_one,
>   		.extra2		= &bpf_jit_limit_max,
>   	},
> +	{
> +		.procname	= "bpf_jit_current",
> +		.data		= &bpf_jit_current,
> +		.maxlen		= sizeof(long),
> +		.mode		= 0400,
> +		.proc_handler	= proc_dolongvec_minmax_bpf_restricted,

Overall series looks good to me. The only nit I would have is that the above could (in theory)
be subject to atomic_long_t vs long type confusion. I would rather prefer to have a small handler
which properly reads out the atomic_long_t and then passes it onwards as a temporary/plain long
to user space.

Thanks,
Daniel

> +	},
>   #endif
>   	{
>   		.procname	= "netdev_tstamp_prequeue",
>