netdev - Re: [PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp

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Date:   Wed, 25 May 2022 14:45:11 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Xu Kuohai <xukuohai@...wei.com>
Cc:     bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        hpa@...or.com, Shuah Khan <shuah@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel Kiss <daniel.kiss@....com>,
        Steven Price <steven.price@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Delyan Kratunov <delyank@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp_flags()

On Wed, May 18, 2022 at 09:16:35AM -0400, Xu Kuohai wrote:
> BPF_TRAM_F_XXX flags are not used by user code and are almost constant
> at compile time, so run time validation is a bit overkill. Remove
> is_valid_bpf_tramp_flags() and add some usage comments.
> 
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> Acked-by: Song Liu <songliubraving@...com>

Am I right in thinking this is independent of the arm64-specific bits, and
could be taken on its own now?

Mark.

> ---
>  arch/x86/net/bpf_jit_comp.c | 20 --------------------
>  kernel/bpf/bpf_struct_ops.c |  3 +++
>  kernel/bpf/trampoline.c     |  3 +++
>  3 files changed, 6 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index a2b6d197c226..7698ef3b4821 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1922,23 +1922,6 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
>  	return 0;
>  }
>  
> -static bool is_valid_bpf_tramp_flags(unsigned int flags)
> -{
> -	if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
> -	    (flags & BPF_TRAMP_F_SKIP_FRAME))
> -		return false;
> -
> -	/*
> -	 * BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
> -	 * and it must be used alone.
> -	 */
> -	if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&
> -	    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
> -		return false;
> -
> -	return true;
> -}
> -
>  /* Example:
>   * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
>   * its 'struct btf_func_model' will be nr_args=2
> @@ -2017,9 +2000,6 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
>  	if (nr_args > 6)
>  		return -ENOTSUPP;
>  
> -	if (!is_valid_bpf_tramp_flags(flags))
> -		return -EINVAL;
> -
>  	/* Generated trampoline stack layout:
>  	 *
>  	 * RBP + 8         [ return address  ]
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index d9a3c9207240..0572cc5aeb28 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -341,6 +341,9 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
>  
>  	tlinks[BPF_TRAMP_FENTRY].links[0] = link;
>  	tlinks[BPF_TRAMP_FENTRY].nr_links = 1;
> +	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
> +	 * and it must be used alone.
> +	 */
>  	flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0;
>  	return arch_prepare_bpf_trampoline(NULL, image, image_end,
>  					   model, flags, tlinks, NULL);
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 93c7675f0c9e..bd3f2e673874 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -358,6 +358,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
>  
>  	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
>  	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)
> +		/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
> +		 * should not be set together.
> +		 */
>  		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
>  
>  	if (ip_arg)
> -- 
> 2.30.2
>