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([2600:1700:6cf8:1240:d241:4a8f:4184:7fb2]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e0ec8be5d2dsm1731584276.16.2024.08.13.16.13.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Aug 2024 16:13:36 -0700 (PDT) Message-ID: <3107f476-b844-4dfa-bcf9-c89baa95cb6f@gmail.com> Date: Tue, 13 Aug 2024 16:13:35 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC bpf-next 2/5] bpf: Handle BPF_KPTR_USER in verifier. To: Alexei Starovoitov Cc: Kui-Feng Lee , bpf , Alexei Starovoitov , Martin KaFai Lau , Song Liu , Kernel Team , Andrii Nakryiko , Kui-Feng Lee References: <20240807235755.1435806-1-thinker.li@gmail.com> <20240807235755.1435806-3-thinker.li@gmail.com> <00ec1572-9f74-4a01-b30a-4eb03489284e@gmail.com> Content-Language: en-US From: Kui-Feng Lee In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/13/24 12:35, Alexei Starovoitov wrote: > On Tue, Aug 13, 2024 at 9:52 AM Kui-Feng Lee wrote: >> >> >> >> On 8/12/24 09:48, Alexei Starovoitov wrote: >>> On Wed, Aug 7, 2024 at 4:58 PM Kui-Feng Lee wrote: >>>> >>>> Give PTR_MAYBE_NULL | PTR_UNTRUSTED | MEM_ALLOC | NON_OWN_REF to kptr_user >>>> to the memory pointed by it readable and writable. >>>> >>>> Signed-off-by: Kui-Feng Lee >>>> --- >>>> kernel/bpf/verifier.c | 11 +++++++++++ >>>> 1 file changed, 11 insertions(+) >>>> >>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>>> index df3be12096cf..84647e599595 100644 >>>> --- a/kernel/bpf/verifier.c >>>> +++ b/kernel/bpf/verifier.c >>>> @@ -5340,6 +5340,10 @@ static int map_kptr_match_type(struct bpf_verifier_env *env, >>>> int perm_flags; >>>> const char *reg_name = ""; >>>> >>>> + if (kptr_field->type == BPF_KPTR_USER) >>>> + /* BPF programs should not change any user kptr */ >>>> + return -EACCES; >>>> + >>>> if (btf_is_kernel(reg->btf)) { >>>> perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU; >>>> >>>> @@ -5483,6 +5487,12 @@ static u32 btf_ld_kptr_type(struct bpf_verifier_env *env, struct btf_field *kptr >>>> ret |= NON_OWN_REF; >>>> } else { >>>> ret |= PTR_UNTRUSTED; >>>> + if (kptr_field->type == BPF_KPTR_USER) >>>> + /* In oder to access directly from bpf >>>> + * programs. NON_OWN_REF make the memory >>>> + * writable. Check check_ptr_to_btf_access(). >>>> + */ >>>> + ret |= MEM_ALLOC | NON_OWN_REF; >>> >>> UNTRUSTED | MEM_ALLOC | NON_OWN_REF ?! >>> >>> That doesn't fit into any of the existing verifier schemes. >>> I cannot make sense of this part. >>> >>> UNTRUSTED | MEM_ALLOC is read only through exceptions logic. >>> The uptr has to be read/write through normal load/store. >> >> I will remove UNTRUSTED and leave MEM_ALLOC and NON_OWN_REF. >> Does it make sense to you? > > I don't think it fits either. > MEM_ALLOC | NON_OWN_REF is specific to bpf_rbtree/linklist nodes. > There are various checks and logic like: > 1. > if (!(type_is_ptr_alloc_obj(reg->type) || > type_is_non_owning_ref(reg->type)) && > WARN_ON_ONCE(reg->off)) > return; > 2. > invalidate_non_owning_refs() during unlock > > that shouldn't apply in this case. > > PTR_TO_MEM with specific mem_size fits better. > Since it's user/kernel shared memory PTR_TO_BTF_ID logic with field walking > won't work anyway, so opaque array of bytes is better. Which is PTR_TO_MEM. Make sense!