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Tue, 15 Sep 2026 01:03:39 -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 v7 5/5] selftests/bpf: Test mm_struct user memory kfuncs with linux_binprm Date: Tue, 15 Sep 2026 11:02:55 +0300 Message-ID: <20260915080255.48929-6-tasos.papagiannnis@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260915080255.48929-1-tasos.papagiannnis@gmail.com> References: <20260915080255.48929-1-tasos.papagiannnis@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a sleepable BPF LSM program attached to bprm_check_security to test bpf_copy_from_user_mm() and bpf_copy_from_user_mm_str() on CONFIG_MMU kernels. Starting at bprm->p, verify that bpf_copy_from_user_mm() can copy the contiguous NUL-separated argument and environment data. Then use bpf_copy_from_user_mm_str() to read each argument and environment string separately, advancing the offset by the length returned from each call. Skip the test on !CONFIG_MMU. In that configuration, exec argument and environment strings remain in bprm->page[] until the binary loader transfers them to the new process stack, so they are not accessible through bprm->mm at the bprm_check_security hook. Signed-off-by: Anastasios Papagiannis --- .../bpf/prog_tests/copy_from_user_bprm.c | 72 +++++++++++ .../selftests/bpf/progs/copy_from_user_bprm.c | 122 ++++++++++++++++++ 2 files changed, 194 insertions(+) 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 diff --git a/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c new file mode 100644 index 000000000000..ef351cda9348 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c @@ -0,0 +1,72 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include + +#include + +#include "copy_from_user_bprm.skel.h" + +void test_copy_from_user_bprm(void) +{ + char arg0[] = "first"; + char arg1[] = "second-argument"; + char env0[] = "SOME_ENV=a"; + char env1[] = "OTHER_ENV=something"; + struct copy_from_user_bprm *skel; + pid_t child; + int status; + + skel = copy_from_user_bprm__open_and_load(); + if (!ASSERT_OK_PTR(skel, "open_and_load")) + return; + + /* + * On !CONFIG_MMU, exec strings are held in bprm->page[] rather than + * being mapped in bprm->mm. + */ + if (!skel->kconfig->CONFIG_MMU) { + printf("%s:SKIP: test requires CONFIG_MMU\n", __func__); + test__skip(); + goto out; + } + + if (!ASSERT_OK(copy_from_user_bprm__attach(skel), "attach")) + goto out; + + child = fork(); + if (!ASSERT_GE(child, 0, "fork")) + goto out; + + if (!child) { + char *const argv[] = { arg0, arg1, NULL }; + char *const envp[] = { env0, env1, NULL }; + + skel->bss->monitored_pid = getpid(); + execvpe("true", argv, envp); + _exit(errno); + } + + if (!ASSERT_EQ(waitpid(child, &status, 0), child, "waitpid")) + goto out; + + if (ASSERT_TRUE(WIFEXITED(status), "child_exited")) + ASSERT_EQ(WEXITSTATUS(status), EPERM, "exec_errno"); + + ASSERT_EQ(skel->bss->bprm_argc, 2, "bprm_argc"); + ASSERT_EQ(skel->bss->bprm_envc, 2, "bprm_envc"); + ASSERT_EQ(skel->bss->data_len_match, 1, "data_len_match"); + ASSERT_EQ(skel->bss->invalid_flags_ret, -EINVAL, "invalid_flags_ret"); + ASSERT_EQ(skel->bss->copy_ret, 0, "copy_ret"); + ASSERT_EQ(skel->bss->str_arg0_ret, sizeof(arg0), "str_arg0_ret"); + ASSERT_EQ(skel->bss->str_arg1_ret, sizeof(arg1), "str_arg1_ret"); + ASSERT_EQ(skel->bss->str_env0_ret, sizeof(env0), "str_env0_ret"); + ASSERT_EQ(skel->bss->str_env1_ret, sizeof(env1), "str_env1_ret"); + ASSERT_EQ(skel->bss->data_match, 1, "data_match"); + ASSERT_EQ(skel->bss->str_args_match, 1, "str_args_match"); + ASSERT_EQ(skel->bss->str_envs_match, 1, "str_envs_match"); + +out: + copy_from_user_bprm__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c new file mode 100644 index 000000000000..07ca96d9db45 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c @@ -0,0 +1,122 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include "vmlinux.h" + +#include +#include +#include + +char _license[] SEC("license") = "GPL"; + +static const char expected_data[] = "first\0second-argument\0" + "SOME_ENV=a\0OTHER_ENV=something"; +static const char expected_arg0[] = "first"; +static const char expected_arg1[] = "second-argument"; +static const char expected_env0[] = "SOME_ENV=a"; +static const char expected_env1[] = "OTHER_ENV=something"; + +int monitored_pid; +int bprm_argc; +int bprm_envc; +int data_len_match; +int invalid_flags_ret; +int copy_ret; +int str_arg0_ret; +int str_arg1_ret; +int str_env0_ret; +int str_env1_ret; +int data_match; +int str_args_match; +int str_envs_match; + +extern bool CONFIG_MMU __kconfig __weak; + +extern int bpf_copy_from_user_mm(void *dst, u32 dst__sz, + const void *unsafe_ptr__ign, + struct mm_struct *mm, u64 flags) __ksym; + +extern int bpf_copy_from_user_mm_str(void *dst, u32 dst__sz, + const void *unsafe_ptr__ign, + struct mm_struct *mm, u64 flags) __ksym; + +SEC("lsm.s/bprm_check_security") +int BPF_PROG(check_exec_args, struct linux_binprm *bprm) +{ + u32 pid = bpf_get_current_pid_tgid() >> 32; + char data[sizeof(expected_data)] = {}; + struct mm_struct *mm; + char arg0[32] = {}; + char arg1[32] = {}; + char env0[32] = {}; + char env1[32] = {}; + u64 offset = 0; + u64 data_len; + + if (!CONFIG_MMU) + return 0; + + if (pid != monitored_pid) + return 0; + + mm = bprm->mm; + if (!mm) + return 0; + + bprm_argc = bprm->argc; + bprm_envc = bprm->envc; + + /* this is the total size of args and envs starting from bprm->p */ + data_len = bprm->exec - bprm->p; + data_len_match = data_len == sizeof(expected_data); + + invalid_flags_ret = bpf_copy_from_user_mm(data, sizeof(data), + (void *)bprm->p, mm, ~0ULL); + + copy_ret = bpf_copy_from_user_mm(data, sizeof(data), (void *)bprm->p, + mm, 0); + if (copy_ret) + return 0; + + data_match = + !__builtin_memcmp(data, expected_data, sizeof(expected_data)); + + /* arg0 is at bprm->p */ + str_arg0_ret = bpf_copy_from_user_mm_str(arg0, sizeof(arg0), + (void *)(bprm->p + offset), + mm, BPF_F_PAD_ZEROS); + if (str_arg0_ret != sizeof(expected_arg0)) + return 0; + offset += str_arg0_ret; + + /* arg1 is at bprm->p + sizeof(arg0) */ + str_arg1_ret = bpf_copy_from_user_mm_str(arg1, sizeof(arg1), + (void *)(bprm->p + offset), + mm, BPF_F_PAD_ZEROS); + if (str_arg1_ret != sizeof(expected_arg1)) + return 0; + offset += str_arg1_ret; + + /* env0 is at bprm->p + sizeof(arg0) + sizeof(arg1) */ + str_env0_ret = bpf_copy_from_user_mm_str(env0, sizeof(env0), + (void *)(bprm->p + offset), + mm, BPF_F_PAD_ZEROS); + if (str_env0_ret != sizeof(expected_env0)) + return 0; + offset += str_env0_ret; + + /* env1 is at bprm->p + sizeof(arg0) + sizeof(arg1) + sizeof(env0) */ + str_env1_ret = bpf_copy_from_user_mm_str(env1, sizeof(env1), + (void *)(bprm->p + offset), + mm, BPF_F_PAD_ZEROS); + if (str_env1_ret != sizeof(expected_env1)) + return 0; + + str_args_match = + !__builtin_memcmp(arg0, expected_arg0, sizeof(expected_arg0)) && + !__builtin_memcmp(arg1, expected_arg1, sizeof(expected_arg1)); + str_envs_match = + !__builtin_memcmp(env0, expected_env0, sizeof(expected_env0)) && + !__builtin_memcmp(env1, expected_env1, sizeof(expected_env1)); + + return data_match && str_args_match && str_envs_match ? -EPERM : 0; +} -- 2.55.0