Re: [PATCH bpf-next] bpf: Check return from set_memory_rox() and friends

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Simon Horman <horms@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>,
	Yonghong Song <yonghong.song@linux.dev>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	David Ahern <dsahern@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	"linux-hardening @ vger . kernel . org"
	<linux-hardening@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Check return from set_memory_rox() and friends
Date: Mon, 19 Feb 2024 10:25:49 +0000	[thread overview]
Message-ID: <2229a6a3-d37b-4865-a479-44df02dfa1d7@csgroup.eu> (raw)
In-Reply-To: <20240219101925.GW40273@kernel.org>

Le 19/02/2024 à 11:19, Simon Horman a écrit :
> 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@csgroup.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.

Ah, thanks,

Indeed I wondered about it and ignored it as I mis-read pack_list as 
pack->list, thinking it would implicitely fly away when droping pack.

I'll send a v2 in a few days once more people have reviewed it.

Christophe