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Fri, 04 Sep 2026 07:54:09 -0700 (PDT) Received: from dell-desktop ([2a02:587:4b5f:900:ef25:2f4:1792:4e6f]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-485885cb03asm6802799f8f.37.2026.09.04.07.54.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 07:54:09 -0700 (PDT) From: Anastasios Papagiannis To: bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, akpm@linux-foundation.org, david@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, kpsingh@kernel.org, matt@bobrowski.net, song@kernel.org, utilityemal77@gmail.com, sun.jian.kdev@gmail.com, tasos.papagiannnis@gmail.com Subject: [PATCH bpf-next v4 0/7] bpf: Add user memory access kfuncs for mm_struct Date: Fri, 4 Sep 2026 17:53:33 +0300 Message-ID: <20260904145340.40212-1-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. Changing bprm->mm to trusted-or-null would otherwise reject existing BPF programs that read through it without a NULL check. Preserve that behavior by allowing fault-protected reads through trusted-or-null BTF pointers. Pointer arithmetic, writes, atomic RMW operations, BPF_LOAD_ACQ accesses, and passing the pointer to a kfunc that requires a non-NULL trusted argument continue to require an explicit NULL check. 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 also adds selftests covering both kfuncs when reading argument and environment strings, and verifier tests covering trusted-or-null BTF pointer reads. 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. - 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. 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 (7): mm: Add copy_remote_mm_str() exec: Clear bprm->mm before dropping its reference bpf: Add user memory access kfuncs for mm_struct bpf: Allow reads through trusted-or-null BTF pointers selftests/bpf: Cover trusted-or-null BTF pointer reads 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/bpf_verifier.h | 9 +- include/linux/mm.h | 2 + kernel/bpf/helpers.c | 142 ++++++++++++++---- kernel/bpf/verifier.c | 17 ++- mm/memory.c | 33 +++- mm/nommu.c | 33 +++- .../selftests/bpf/prog_tests/bpf_iter.c | 6 +- .../bpf/prog_tests/copy_from_user_bprm.c | 72 +++++++++ .../prog_tests/test_struct_ops_maybe_null.c | 13 +- .../bpf/prog_tests/tp_btf_nullable.c | 28 ++++ .../selftests/bpf/progs/copy_from_user_bprm.c | 123 +++++++++++++++ .../selftests/bpf/progs/raw_tp_null_fail.c | 75 ++++++++- .../bpf/progs/test_tp_btf_nullable.c | 45 +++++- .../bpf/progs/test_tp_btf_nullable_runtime.c | 35 +++++ .../selftests/bpf/progs/verifier_lsm.c | 18 ++- .../selftests/bpf/progs/verifier_vfs_accept.c | 14 ++ .../selftests/bpf/progs/verifier_vfs_reject.c | 14 -- .../selftests/bpf/test_kmods/bpf_testmod.c | 1 + .../sched_ext/maybe_null_fail_dsp.bpf.c | 5 +- 20 files changed, 616 insertions(+), 76 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 create mode 100644 tools/testing/selftests/bpf/progs/test_tp_btf_nullable_runtime.c base-commit: 7bf591f26545f5776a4e42d08c06fd94469766dd -- 2.55.0