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([2620:10d:c090:500::3:3a6d]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-12742cba118sm20594390c88.12.2026.02.17.17.48.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Feb 2026 17:48:55 -0800 (PST) Message-ID: Subject: Re: [PATCH bpf-next v2 0/2] bpf: Add multi-level pointer parameter support for trampolines From: Eduard Zingerman To: Slava Imameev , ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Cc: martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-open-source@crowdstrike.com Date: Tue, 17 Feb 2026 17:48:53 -0800 In-Reply-To: <20260217221357.18215-1-slava.imameev@crowdstrike.com> References: <20260217221357.18215-1-slava.imameev@crowdstrike.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-02-18 at 09:13 +1100, Slava Imameev wrote: [...] > The verifier assigns SCALAR type to single-level pointers (void*, int*). So, the simplest change for pointers to pointers would be as below, right? --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -6906,7 +6906,8 @@ bool btf_ctx_access(int off, int size, enum bpf_acc= ess_type type, * If it's a pointer to void, it's the same as scalar from the ve= rifier * safety POV. Either way, no futher pointer walking is allowed. */ - if (is_void_or_int_ptr(btf, t)) + if (is_void_or_int_ptr(btf, t) || !is_ptr_to_struct(btf, t)) return true; /* this is a pointer to another type */ Except that loaded value would be marked as scalar() and one would need to cast it using e.g. bpf_core_cast() to obtain an untrusted pointer. > For multi-level pointers, I selected PTR_TO_MEM to enable memory access > through a single load instruction for the first level of dereference, > with subsequent dereferences becoming SCALAR. This design eliminates > helper call for parameter dereference, replacing it with a load > instruction (e.g., void* ptr =3D *pptr). If going this route instead, is there a technical reason to limit this logic to multi-level pointers? Applying same rules to `int *` and alike seem more consistent. [...]