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Fri, 18 Sep 2026 06:18:17 -0700 (PDT) Received: from dell-desktop ([2a02:587:4b4e:8500:290c:210b:1c76:5710]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4871feb5de3sm4424549f8f.1.2026.09.18.06.18.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 06:18:16 -0700 (PDT) From: Anastasios Papagiannis To: bpf@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, akpm@linux-foundation.org, andrii@kernel.org, ast@kernel.org, brauner@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, kpsingh@kernel.org, ljs@kernel.org, matt@bobrowski.net, memxor@gmail.com, song@kernel.org, sun.jian.kdev@gmail.com, utilityemal77@gmail.com, viro@zeniv.linux.org.uk, tasos.papagiannnis@gmail.com Subject: [PATCH bpf-next v9 0/5] bpf: Add user memory access kfuncs for mm_struct Date: Fri, 18 Sep 2026 16:17:52 +0300 Message-ID: <20260918131757.42802-1-tasos.papagiannnis@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On MMU systems, during exec, argument and environment strings are copied into the new address space held by struct linux_binprm before that address space is installed on the task_struct. Existing BPF user memory helpers operate on the current address space or one associated with a task_struct. Because no task_struct refers to the new address space at this point, programs cannot access these strings from the bprm_check_security LSM hook. This series adds two sleepable BPF kfuncs for copying bytes or NUL-terminated strings from a trusted struct mm_struct. It also marks linux_binprm->mm as trusted-or-null, allowing BPF LSM programs to pass it to the kfuncs after a NULL check and inspect exec arguments before allowing the exec to continue. To make the trusted-or-null annotation safe, the exec paths are hardened to clear bprm->mm before dropping the reference it owns. On NOMMU systems, exec argument and environment strings remain in bprm->page[] until they are transferred to the new process stack. They cannot be accessed through bprm->mm at the bprm_check_security hook. The new kfuncs remain available on NOMMU for address ranges represented by a supplied struct mm_struct. The series adds selftests covering both kfuncs while reading argument and environment strings from linux_binprm during exec. Changes in v9: - Acquire a reference to mm_struct in bpf_copy_from_user_mm() and bpf_copy_from_user_mm_str() to protect against concurrent free operations and prevent a potential Use-After-Free in future use-cases. - Fix indentation in the remaining mm patches. Changes in v8: - Removed CONFIG_BPF_SYSCALL #ifdefs from mm/memory.c and mm/nommu.c. - Reformatted the selftest to use 120-character lines. - Removed the CONFIG_MMU check from the selftests. - Removed the extern declarations from the selftests, as they already exist in vmlinux.h. - Moved the checks to user space in the selftests. Changes in v7: - Use execvpe() instead of a hardcoded /bin/true path in the copy_from_user_bprm selftest while retaining the controlled environment. - Remove the unused bpf_misc.h include. - Rewrap the invalid-flags kfunc call to stay within 80 columns. - Fix indent in mm patches. Changes in v6: - Drop redundant extern keywords and CONFIG_BPF_SYSCALL guards from the remote memory copy declarations. - Drop the explicit bpf_copy_from_user_mm() prototype and share copy logic through inlineable static internal helpers instead of calling between kfunc/helper entry points. - Validate flags and zero-length requests before acquiring the task's mm, preserving existing behavior and ensuring internal helpers are called only with a live mm. - Drop the verifier relaxation for unchecked reads through trusted-or-null pointers and its tests. - Fix the existing LSM selftest to explicitly NULL-check bprm->mm after marking the field trusted-or-null. Changes in v5: - Move the shared wrappers to mm/util.c and handle zero-length requests at the entry points. Changes in v4: - Add negative verifier tests for atomic RMW and load-acquire accesses through trusted-or-null BTF pointers. - Preserve explicit nullability-marking coverage for tracepoint arguments, dentry->d_inode, and sched_ext .dispatch. - Use the already-nullable mmap_file argument for the negative store test, avoiding dependency on the later linux_binprm->mm marking. - Clarify the bprm->mm lifetime invariant and move its lifetime fix before the mm_struct kfunc patch. - Reword the trusted-or-null read change in imperative mood and remove its redundant before-and-after summary. - Document that the existing task-based user-memory interfaces delegate to the new mm-based implementations, reorder the string-copy kfuncs to remove an unnecessary declaration, and annotate the remaining declaration with __bpf_kfunc. Changes in v3: - Replace the linux_binprm-specific kfuncs with generic struct mm_struct kfuncs, as suggested by Andrii Nakryiko. - Move the kfuncs next to the existing user memory helpers and make the task-based variants delegate to the new mm-based implementations, as suggested by Andrii Nakryiko. - Clear bprm->mm before dropping its reference on exec error paths. - Mark linux_binprm->mm as trusted-or-null. - Allow fault-protected reads through trusted-or-null BTF pointers to preserve compatibility with existing BPF programs, as suggested by Andrii Nakryiko. - Add verifier and runtime selftests for trusted-or-null BTF pointer reads. - Rename __copy_remote_vm_str() to __copy_remote_mm_str(), as suggested by Andrii Nakryiko. - Clarify that reading exec strings through bprm->mm is limited to MMU systems, while the generic mm-based kfuncs remain available on NOMMU. Changes in v2: - Register the kfuncs on NOMMU systems and return -EOPNOTSUPP when called, as suggested by Justin Suess. - Add selftest coverage for reading environment strings, as suggested by Justin Suess. - Clarify that copy_remote_mm_str() leaves the destination untouched when called with a zero-length buffer. - Use sizeof() instead of hardcoded argument lengths in the selftests. - Use ~0ULL for invalid-flags checks in the selftests. v8: https://lore.kernel.org/bpf/20260918091058.297740-1-tasos.papagiannnis@gmail.com/ v7: https://lore.kernel.org/bpf/20260915080255.48929-1-tasos.papagiannnis@gmail.com/ v6: https://lore.kernel.org/all/20260908135302.74963-1-tasos.papagiannnis@gmail.com/ v5: https://lore.kernel.org/bpf/20260907165220.52431-1-tasos.papagiannnis@gmail.com/ v4: https://lore.kernel.org/bpf/20260904145340.40212-1-tasos.papagiannnis@gmail.com/ v3: https://lore.kernel.org/bpf/20260831092305.42062-1-tasos.papagiannnis@gmail.com/ v2: https://lore.kernel.org/bpf/20260820131801.68759-1-tasos.papagiannnis@gmail.com/ v1: https://lore.kernel.org/bpf/20260812111140.7762-1-tasos.papagiannnis@gmail.com/ Anastasios Papagiannis (5): mm: Add copy_remote_mm_str() exec: Clear bprm->mm before dropping its reference bpf: Add user memory access kfuncs for mm_struct bpf: Mark linux_binprm->mm as trusted-or-null selftests/bpf: Test mm_struct user memory kfuncs with linux_binprm fs/exec.c | 7 +- include/linux/mm.h | 8 +- kernel/bpf/helpers.c | 154 ++++++++++++++++-- kernel/bpf/verifier.c | 5 + mm/internal.h | 3 + mm/memory.c | 43 +---- mm/nommu.c | 43 +---- mm/util.c | 60 +++++++ .../bpf/prog_tests/copy_from_user_bprm.c | 65 ++++++++ .../selftests/bpf/progs/copy_from_user_bprm.c | 69 ++++++++ tools/testing/selftests/bpf/progs/lsm.c | 5 +- 11 files changed, 361 insertions(+), 101 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c create mode 100644 tools/testing/selftests/bpf/progs/copy_from_user_bprm.c base-commit: 961b8946acb482b6d7a39c266d623e5f9c4e873f -- 2.55.0