linux-hardening - Re: [PATCH bpf-next] bpf: Check return from set_memory

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Date: Mon, 19 Feb 2024 10:19:25 +0000
From: Simon Horman <horms@...nel.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	"linux-hardening @ vger . kernel . org" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Check return from set_memory_rox() and
 friends

On Sat, Feb 17, 2024 at 11:24:07AM +0100, Christophe Leroy wrote:
> arch_protect_bpf_trampoline() and alloc_new_pack() call
> set_memory_rox() which can fail, leading to unprotected memory.
> 
> Take into account return from set_memory_XX() functions and add
> __must_check flag to arch_protect_bpf_trampoline().
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

...

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ea6843be2616..23ce17da3bf7 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -898,23 +898,30 @@ static LIST_HEAD(pack_list);
>  static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_insns)
>  {
>  	struct bpf_prog_pack *pack;
> +	int err;
>  
>  	pack = kzalloc(struct_size(pack, bitmap, BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)),
>  		       GFP_KERNEL);
>  	if (!pack)
>  		return NULL;
>  	pack->ptr = bpf_jit_alloc_exec(BPF_PROG_PACK_SIZE);
> -	if (!pack->ptr) {
> -		kfree(pack);
> -		return NULL;
> -	}
> +	if (!pack->ptr)
> +		goto out;
>  	bpf_fill_ill_insns(pack->ptr, BPF_PROG_PACK_SIZE);
>  	bitmap_zero(pack->bitmap, BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE);
>  	list_add_tail(&pack->list, &pack_list);

Hi Christophe,

Here pack is added to pack_list.

>  
>  	set_vm_flush_reset_perms(pack->ptr);
> -	set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
> +	err = set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
> +	if (err)
> +		goto out_free;

But this unwind path doesn't appear to remove pack form pack_list.

Flagged by Smatch.

>  	return pack;
> +
> +out_free:
> +	bpf_jit_free_exec(pack->ptr);
> +out:
> +	kfree(pack);
> +	return NULL;
>  }
>  
>  void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)

...