[PATCH v3 bpf-next 0/5] Add bpf_getxattr

[PATCH v3 bpf-next 0/5] Add bpf_getxattr

[KP Singh]

v2 -> v3

- Fixed missing prototype error
- Fixes suggested by other Joanne and Kumar.

v1 -> v2

- Used kfuncs as suggested by Alexei
- Used Benjamin Tissoires' patch from the HID v4 series to add a
  sleepable kfunc set (I sent the patch as a part of this series as it
  seems to have been dropped from v5) and acked it. Hope this is okay.
- Added support for verifying string constants to kfuncs

Foundation for building more complex security policies using the
BPF LSM as presented in LSF/MM/BPF:

 http://vger.kernel.org/bpfconf2022_material/lsfmmbpf2022-xattr.pdf

Benjamin Tissoires (1):
  btf: Add a new kfunc set which allows to mark a function to be
    sleepable

KP Singh (4):
  bpf: kfunc support for ARG_PTR_TO_CONST_STR
  bpf: Allow kfuncs to be used in LSM programs
  bpf: Add a bpf_getxattr kfunc
  bpf/selftests: Add a selftest for bpf_getxattr

 include/linux/bpf_verifier.h                  |  2 +
 include/linux/btf.h                           |  2 +
 kernel/bpf/btf.c                              | 39 +++++++-
 kernel/bpf/verifier.c                         | 89 +++++++++++--------
 kernel/trace/bpf_trace.c                      | 42 +++++++++
 .../testing/selftests/bpf/prog_tests/xattr.c  | 58 ++++++++++++
 tools/testing/selftests/bpf/progs/xattr.c     | 37 ++++++++
 7 files changed, 229 insertions(+), 40 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xattr.c
 create mode 100644 tools/testing/selftests/bpf/progs/xattr.c

-- 
2.37.0.rc0.104.g0611611a94-goog

[PATCH v3 bpf-next 1/5] btf: Add a new kfunc set which allows to mark a function to be sleepable

[KP Singh]

From: Benjamin Tissoires <benjamin.tissoires@redhat.com>

This allows to declare a kfunc as sleepable and prevents its use in
a non sleepable program.

Acked-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/btf.h |  2 ++
 kernel/bpf/btf.c    | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 1bfed7fa0428..6e7517573d9e 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -18,6 +18,7 @@ enum btf_kfunc_type {
 	BTF_KFUNC_TYPE_RELEASE,
 	BTF_KFUNC_TYPE_RET_NULL,
 	BTF_KFUNC_TYPE_KPTR_ACQUIRE,
+	BTF_KFUNC_TYPE_SLEEPABLE,
 	BTF_KFUNC_TYPE_MAX,
 };
 
@@ -37,6 +38,7 @@ struct btf_kfunc_id_set {
 			struct btf_id_set *release_set;
 			struct btf_id_set *ret_null_set;
 			struct btf_id_set *kptr_acquire_set;
+			struct btf_id_set *sleepable_set;
 		};
 		struct btf_id_set *sets[BTF_KFUNC_TYPE_MAX];
 	};
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f08037c31dd7..668ecf61649b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6171,7 +6171,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 	struct bpf_verifier_log *log = &env->log;
 	u32 i, nargs, ref_id, ref_obj_id = 0;
 	bool is_kfunc = btf_is_kernel(btf);
-	bool rel = false, kptr_get = false;
+	bool rel = false, kptr_get = false, sleepable = false;
 	const char *func_name, *ref_tname;
 	const struct btf_type *t, *ref_t;
 	const struct btf_param *args;
@@ -6202,9 +6202,10 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 	}
 
 	if (is_kfunc) {
-		/* Only kfunc can be release func */
 		rel = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
 						BTF_KFUNC_TYPE_RELEASE, func_id);
+		sleepable = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
+						      BTF_KFUNC_TYPE_SLEEPABLE, func_id);
 		kptr_get = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
 						     BTF_KFUNC_TYPE_KPTR_ACQUIRE, func_id);
 	}
@@ -6404,6 +6405,13 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 			func_name);
 		return -EINVAL;
 	}
+
+	if (sleepable && !env->prog->aux->sleepable) {
+		bpf_log(log, "kernel function %s is sleepable but the program is not\n",
+			func_name);
+		return -EINVAL;
+	}
+
 	/* returns argument register number > 0 in case of reference release kfunc */
 	return rel ? ref_regno : 0;
 }
-- 
2.37.0.rc0.104.g0611611a94-goog

[PATCH v3 bpf-next 2/5] bpf: kfunc support for ARG_PTR_TO_CONST_STR

[KP Singh]

kfuncs can handle pointers to memory when the next argument is
the size of the memory that can be read and verify these as
ARG_CONST_SIZE_OR_ZERO

Similarly add support for string constants (const char *) and
verify it similar to ARG_PTR_TO_CONST_STR.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/bpf_verifier.h |  2 +
 kernel/bpf/btf.c             | 26 +++++++++++
 kernel/bpf/verifier.c        | 89 +++++++++++++++++++++---------------
 3 files changed, 79 insertions(+), 38 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 3930c963fa67..60d490354397 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -548,6 +548,8 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
 			     u32 regno);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 		   u32 regno, u32 mem_size);
+int check_const_str(struct bpf_verifier_env *env,
+		    const struct bpf_reg_state *reg, int regno);
 
 /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
 static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 668ecf61649b..6608e8a0c5ca 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6162,6 +6162,23 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
 	return true;
 }
 
+static bool btf_param_is_const_str_ptr(const struct btf *btf,
+				       const struct btf_param *param)
+{
+	const struct btf_type *t;
+
+	t = btf_type_by_id(btf, param->type);
+	if (!btf_type_is_ptr(t))
+		return false;
+
+	t = btf_type_by_id(btf, t->type);
+	if (!(BTF_INFO_KIND(t->info) == BTF_KIND_CONST))
+		return false;
+
+	t = btf_type_skip_modifiers(btf, t->type, NULL);
+	return !strcmp(btf_name_by_offset(btf, t->name_off), "char");
+}
+
 static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				    const struct btf *btf, u32 func_id,
 				    struct bpf_reg_state *regs,
@@ -6344,6 +6361,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 		} else if (ptr_to_mem_ok) {
 			const struct btf_type *resolve_ret;
 			u32 type_size;
+			int err;
 
 			if (is_kfunc) {
 				bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
@@ -6354,6 +6372,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				 * When arg_mem_size is true, the pointer can be
 				 * void *.
 				 */
+				if (btf_param_is_const_str_ptr(btf, &args[i])) {
+					err = check_const_str(env, reg, regno);
+					if (err < 0)
+						return err;
+					i++;
+					continue;
+				}
+
 				if (!btf_type_is_scalar(ref_t) &&
 				    !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
 				    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2859901ffbe3..7ac501122df0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5840,6 +5840,56 @@ static u32 stack_slot_get_id(struct bpf_verifier_env *env, struct bpf_reg_state
 	return state->stack[spi].spilled_ptr.id;
 }
 
+int check_const_str(struct bpf_verifier_env *env,
+		    const struct bpf_reg_state *reg, int regno)
+{
+	struct bpf_map *map;
+	int map_off;
+	u64 map_addr;
+	char *str_ptr;
+	int err;
+
+	if (reg->type != PTR_TO_MAP_VALUE)
+		return -EACCES;
+
+	map = reg->map_ptr;
+	if (!bpf_map_is_rdonly(map)) {
+		verbose(env, "R%d does not point to a readonly map'\n", regno);
+		return -EACCES;
+	}
+
+	if (!tnum_is_const(reg->var_off)) {
+		verbose(env, "R%d is not a constant address'\n", regno);
+		return -EACCES;
+	}
+
+	if (!map->ops->map_direct_value_addr) {
+		verbose(env,
+			"no direct value access support for this map type\n");
+		return -EACCES;
+	}
+
+	err = check_map_access(env, regno, reg->off, map->value_size - reg->off,
+			       false, ACCESS_HELPER);
+	if (err)
+		return err;
+
+	map_off = reg->off + reg->var_off.value;
+	err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
+	if (err) {
+		verbose(env, "direct value access on string failed\n");
+		return err;
+	}
+
+	str_ptr = (char *)(long)(map_addr);
+	if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
+		verbose(env, "string is not zero-terminated\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			  struct bpf_call_arg_meta *meta,
 			  const struct bpf_func_proto *fn)
@@ -6074,44 +6124,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			return err;
 		err = check_ptr_alignment(env, reg, 0, size, true);
 	} else if (arg_type == ARG_PTR_TO_CONST_STR) {
-		struct bpf_map *map = reg->map_ptr;
-		int map_off;
-		u64 map_addr;
-		char *str_ptr;
-
-		if (!bpf_map_is_rdonly(map)) {
-			verbose(env, "R%d does not point to a readonly map'\n", regno);
-			return -EACCES;
-		}
-
-		if (!tnum_is_const(reg->var_off)) {
-			verbose(env, "R%d is not a constant address'\n", regno);
-			return -EACCES;
-		}
-
-		if (!map->ops->map_direct_value_addr) {
-			verbose(env, "no direct value access support for this map type\n");
-			return -EACCES;
-		}
-
-		err = check_map_access(env, regno, reg->off,
-				       map->value_size - reg->off, false,
-				       ACCESS_HELPER);
-		if (err)
-			return err;
-
-		map_off = reg->off + reg->var_off.value;
-		err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
-		if (err) {
-			verbose(env, "direct value access on string failed\n");
-			return err;
-		}
-
-		str_ptr = (char *)(long)(map_addr);
-		if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
-			verbose(env, "string is not zero-terminated\n");
-			return -EINVAL;
-		}
+		err = check_const_str(env, reg, regno);
 	} else if (arg_type == ARG_PTR_TO_KPTR) {
 		if (process_kptr_func(env, regno, meta))
 			return -EACCES;
-- 
2.37.0.rc0.104.g0611611a94-goog

[PATCH v3 bpf-next 3/5] bpf: Allow kfuncs to be used in LSM programs

[KP Singh]

In preparation for the addition of bpf_getxattr kfunc.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 kernel/bpf/btf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6608e8a0c5ca..c48566dc86fe 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7261,6 +7261,7 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
 	case BPF_PROG_TYPE_STRUCT_OPS:
 		return BTF_KFUNC_HOOK_STRUCT_OPS;
 	case BPF_PROG_TYPE_TRACING:
+	case BPF_PROG_TYPE_LSM:
 		return BTF_KFUNC_HOOK_TRACING;
 	case BPF_PROG_TYPE_SYSCALL:
 		return BTF_KFUNC_HOOK_SYSCALL;
-- 
2.37.0.rc0.104.g0611611a94-goog

[PATCH v3 bpf-next 4/5] bpf: Add a bpf_getxattr kfunc

[KP Singh]

LSMs like SELinux store security state in xattrs. bpf_getxattr enables
BPF LSM to implement similar functionality. In combination with
bpf_local_storage, xattrs can be used to develop more complex security
policies.

This kfunc wraps around __vfs_getxattr which can sleep and is,
therefore, limited to sleepable programs using the newly added
sleepable_set for kfuncs.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4be976cf7d63..210e29bd0cbb 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -20,6 +20,7 @@
 #include <linux/fprobe.h>
 #include <linux/bsearch.h>
 #include <linux/sort.h>
+#include <linux/xattr.h>
 
 #include <net/bpf_sk_storage.h>
 
@@ -1181,6 +1182,47 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
 	.arg1_type	= ARG_PTR_TO_CTX,
 };
 
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+		  "kfuncs which will be used in BPF programs");
+
+noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
+				     const char *name, void *value, int size)
+{
+	return __vfs_getxattr(dentry, inode, name, value, size);
+}
+
+__diag_pop();
+
+BTF_SET_START(bpf_trace_kfunc_ids)
+BTF_ID(func, bpf_getxattr)
+BTF_SET_END(bpf_trace_kfunc_ids)
+
+BTF_SET_START(bpf_trace_sleepable_kfunc_ids)
+BTF_ID(func, bpf_getxattr)
+BTF_SET_END(bpf_trace_sleepable_kfunc_ids)
+
+static const struct btf_kfunc_id_set bpf_trace_kfunc_set = {
+	.owner = THIS_MODULE,
+	.check_set = &bpf_trace_kfunc_ids,
+	.sleepable_set = &bpf_trace_sleepable_kfunc_ids,
+};
+
+static int __init bpf_trace_kfunc_init(void)
+{
+	int ret;
+
+	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
+					&bpf_trace_kfunc_set);
+	if (!ret)
+		return ret;
+
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,
+					&bpf_trace_kfunc_set);
+
+}
+late_initcall(bpf_trace_kfunc_init);
+
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
-- 
2.37.0.rc0.104.g0611611a94-goog

[PATCH v3 bpf-next 5/5] bpf/selftests: Add a selftest for bpf_getxattr

[KP Singh]

A simple test that adds an xattr on a copied /bin/ls and reads it back
when the copied ls is executed.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 .../testing/selftests/bpf/prog_tests/xattr.c  | 58 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/xattr.c     | 37 ++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xattr.c
 create mode 100644 tools/testing/selftests/bpf/progs/xattr.c

diff --git a/tools/testing/selftests/bpf/prog_tests/xattr.c b/tools/testing/selftests/bpf/prog_tests/xattr.c
new file mode 100644
index 000000000000..442b6c1aed0e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xattr.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2022 Google LLC.
+ */
+
+#include <test_progs.h>
+#include <sys/xattr.h>
+#include "xattr.skel.h"
+
+#define XATTR_NAME "security.bpf"
+#define XATTR_VALUE "test_progs"
+
+static unsigned int duration;
+
+void test_xattr(void)
+{
+	struct xattr *skel = NULL;
+	char tmp_dir_path[] = "/tmp/xattrXXXXXX";
+	char tmp_exec_path[64];
+	char cmd[256];
+	int err;
+
+	if (CHECK(!mkdtemp(tmp_dir_path), "mkdtemp",
+		  "unable to create tmpdir: %d\n", errno))
+		goto close_prog;
+
+	snprintf(tmp_exec_path, sizeof(tmp_exec_path), "%s/copy_of_ls",
+		 tmp_dir_path);
+	snprintf(cmd, sizeof(cmd), "cp /bin/ls %s", tmp_exec_path);
+	if (CHECK_FAIL(system(cmd)))
+		goto close_prog_rmdir;
+
+	if (CHECK(setxattr(tmp_exec_path, XATTR_NAME, XATTR_VALUE,
+			   sizeof(XATTR_VALUE), 0),
+		  "setxattr", "unable to setxattr: %d", errno))
+		goto close_prog_rmdir;
+
+	skel = xattr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_load"))
+		goto close_prog_rmdir;
+
+	err = xattr__attach(skel);
+	if (!ASSERT_OK(err, "xattr__attach failed"))
+		goto close_prog_rmdir;
+
+	snprintf(cmd, sizeof(cmd), "%s -l", tmp_exec_path);
+	if (CHECK_FAIL(system(cmd)))
+		goto close_prog_rmdir;
+
+	ASSERT_EQ(skel->bss->result, 1, "xattr result");
+
+close_prog_rmdir:
+	snprintf(cmd, sizeof(cmd), "rm -rf %s", tmp_dir_path);
+	system(cmd);
+close_prog:
+	xattr__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/xattr.c b/tools/testing/selftests/bpf/progs/xattr.c
new file mode 100644
index 000000000000..ccc078fb8ebd
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/xattr.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2022 Google LLC.
+ */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+#define XATTR_NAME "security.bpf"
+#define XATTR_VALUE "test_progs"
+
+__u64 result = 0;
+
+extern ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
+			    const char *name, void *value, int size) __ksym;
+
+SEC("lsm.s/bprm_committed_creds")
+void BPF_PROG(bprm_cc, struct linux_binprm *bprm)
+{
+	struct task_struct *current = bpf_get_current_task_btf();
+	char dir_xattr_value[64] = {0};
+	int xattr_sz = 0;
+
+	xattr_sz = bpf_getxattr(bprm->file->f_path.dentry,
+				bprm->file->f_path.dentry->d_inode, XATTR_NAME,
+				dir_xattr_value, 64);
+
+	if (xattr_sz <= 0)
+		return;
+
+	if (!bpf_strncmp(dir_xattr_value, sizeof(XATTR_VALUE), XATTR_VALUE))
+		result = 1;
+}
-- 
2.37.0.rc0.104.g0611611a94-goog

Re: [PATCH v3 bpf-next 1/5] btf: Add a new kfunc set which allows to mark a function to be sleepable

[KP Singh]

On Tue, Jun 21, 2022 at 3:46 PM KP Singh <kpsingh@kernel.org> wrote:
>
> From: Benjamin Tissoires <benjamin.tissoires@redhat.com>
>
> This allows to declare a kfunc as sleepable and prevents its use in
> a non sleepable program.
>
> Acked-by: KP Singh <kpsingh@kernel.org>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> Signed-off-by: KP Singh <kpsingh@kernel.org>

Please feel free to drop this, this is my broken "automation".

Re: [PATCH v3 bpf-next 2/5] bpf: kfunc support for ARG_PTR_TO_CONST_STR

[Kumar Kartikeya Dwivedi]

On Wed, Jun 22, 2022 at 02:16:39AM IST, KP Singh wrote:
> kfuncs can handle pointers to memory when the next argument is
> the size of the memory that can be read and verify these as
> ARG_CONST_SIZE_OR_ZERO
>
> Similarly add support for string constants (const char *) and
> verify it similar to ARG_PTR_TO_CONST_STR.
>
> Signed-off-by: KP Singh <kpsingh@kernel.org>
> ---
>  include/linux/bpf_verifier.h |  2 +
>  kernel/bpf/btf.c             | 26 +++++++++++
>  kernel/bpf/verifier.c        | 89 +++++++++++++++++++++---------------
>  3 files changed, 79 insertions(+), 38 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 3930c963fa67..60d490354397 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -548,6 +548,8 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
>  			     u32 regno);
>  int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
>  		   u32 regno, u32 mem_size);
> +int check_const_str(struct bpf_verifier_env *env,
> +		    const struct bpf_reg_state *reg, int regno);
>
>  /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
>  static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 668ecf61649b..6608e8a0c5ca 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6162,6 +6162,23 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
>  	return true;
>  }
>
> +static bool btf_param_is_const_str_ptr(const struct btf *btf,
> +				       const struct btf_param *param)
> +{
> +	const struct btf_type *t;
> +
> +	t = btf_type_by_id(btf, param->type);
> +	if (!btf_type_is_ptr(t))
> +		return false;
> +
> +	t = btf_type_by_id(btf, t->type);
> +	if (!(BTF_INFO_KIND(t->info) == BTF_KIND_CONST))
> +		return false;
> +

Forgot to change this to !=.

> +	t = btf_type_skip_modifiers(btf, t->type, NULL);
> +	return !strcmp(btf_name_by_offset(btf, t->name_off), "char");
> +}
> +
>  static int btf_check_func_arg_match(struct bpf_verifier_env *env,
>  				    const struct btf *btf, u32 func_id,
>  				    struct bpf_reg_state *regs,
> @@ -6344,6 +6361,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
>  		} else if (ptr_to_mem_ok) {
>  			const struct btf_type *resolve_ret;
>  			u32 type_size;
> +			int err;
>
>  			if (is_kfunc) {
>  				bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
> @@ -6354,6 +6372,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
>  				 * When arg_mem_size is true, the pointer can be
>  				 * void *.
>  				 */
> +				if (btf_param_is_const_str_ptr(btf, &args[i])) {
> +					err = check_const_str(env, reg, regno);
> +					if (err < 0)
> +						return err;
> +					i++;

Sorry for not seeing it before, I think this i++ is incorrect. It is skipping
over the next argument. Which means mem, len pair is not being seen, otherwise
it should have given an error with the void * argument, because the next
argument does not have __sz prefix, so there is no mem, len pair in the kfunc
args.

The i++ is done for arg_mem_size case because we processed both argno and argno + 1
together, so the next size arg doesn't need to be processed.

So the bpf_getxattr declaration needs to change from:

noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
				     const char *name, void *value, int size)

to

noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
				     const char *name, void *value, int value__sz)

You only need the __sz suffix, the part before that is your choice.
Then it will actually check the size for the value pointer.
Also, I think neither noinline nor __weak are needed.

> +					continue;
> +				}
> +
>  				if (!btf_type_is_scalar(ref_t) &&
>  				    !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
>  				    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2859901ffbe3..7ac501122df0 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5840,6 +5840,56 @@ static u32 stack_slot_get_id(struct bpf_verifier_env *env, struct bpf_reg_state
>  	return state->stack[spi].spilled_ptr.id;
>  }
>
> +int check_const_str(struct bpf_verifier_env *env,
> +		    const struct bpf_reg_state *reg, int regno)
> +{
> +	struct bpf_map *map;
> +	int map_off;
> +	u64 map_addr;
> +	char *str_ptr;
> +	int err;
> +
> +	if (reg->type != PTR_TO_MAP_VALUE)
> +		return -EACCES;
> +
> +	map = reg->map_ptr;
> +	if (!bpf_map_is_rdonly(map)) {
> +		verbose(env, "R%d does not point to a readonly map'\n", regno);
> +		return -EACCES;
> +	}
> +
> +	if (!tnum_is_const(reg->var_off)) {
> +		verbose(env, "R%d is not a constant address'\n", regno);
> +		return -EACCES;
> +	}
> +
> +	if (!map->ops->map_direct_value_addr) {
> +		verbose(env,
> +			"no direct value access support for this map type\n");
> +		return -EACCES;
> +	}
> +
> +	err = check_map_access(env, regno, reg->off, map->value_size - reg->off,
> +			       false, ACCESS_HELPER);
> +	if (err)
> +		return err;
> +
> +	map_off = reg->off + reg->var_off.value;
> +	err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
> +	if (err) {
> +		verbose(env, "direct value access on string failed\n");
> +		return err;
> +	}
> +
> +	str_ptr = (char *)(long)(map_addr);
> +	if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
> +		verbose(env, "string is not zero-terminated\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
>  			  struct bpf_call_arg_meta *meta,
>  			  const struct bpf_func_proto *fn)
> @@ -6074,44 +6124,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
>  			return err;
>  		err = check_ptr_alignment(env, reg, 0, size, true);
>  	} else if (arg_type == ARG_PTR_TO_CONST_STR) {
> -		struct bpf_map *map = reg->map_ptr;
> -		int map_off;
> -		u64 map_addr;
> -		char *str_ptr;
> -
> -		if (!bpf_map_is_rdonly(map)) {
> -			verbose(env, "R%d does not point to a readonly map'\n", regno);
> -			return -EACCES;
> -		}
> -
> -		if (!tnum_is_const(reg->var_off)) {
> -			verbose(env, "R%d is not a constant address'\n", regno);
> -			return -EACCES;
> -		}
> -
> -		if (!map->ops->map_direct_value_addr) {
> -			verbose(env, "no direct value access support for this map type\n");
> -			return -EACCES;
> -		}
> -
> -		err = check_map_access(env, regno, reg->off,
> -				       map->value_size - reg->off, false,
> -				       ACCESS_HELPER);
> -		if (err)
> -			return err;
> -
> -		map_off = reg->off + reg->var_off.value;
> -		err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
> -		if (err) {
> -			verbose(env, "direct value access on string failed\n");
> -			return err;
> -		}
> -
> -		str_ptr = (char *)(long)(map_addr);
> -		if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
> -			verbose(env, "string is not zero-terminated\n");
> -			return -EINVAL;
> -		}
> +		err = check_const_str(env, reg, regno);
>  	} else if (arg_type == ARG_PTR_TO_KPTR) {
>  		if (process_kptr_func(env, regno, meta))
>  			return -EACCES;
> --
> 2.37.0.rc0.104.g0611611a94-goog
>

--
Kartikeya

Re: [PATCH v3 bpf-next 2/5] bpf: kfunc support for ARG_PTR_TO_CONST_STR

[KP Singh]

On Tue, Jun 21, 2022 at 8:27 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Wed, Jun 22, 2022 at 02:16:39AM IST, KP Singh wrote:
> > kfuncs can handle pointers to memory when the next argument is
> > the size of the memory that can be read and verify these as
> > ARG_CONST_SIZE_OR_ZERO
> >
> > Similarly add support for string constants (const char *) and
> > verify it similar to ARG_PTR_TO_CONST_STR.
> >
> > Signed-off-by: KP Singh <kpsingh@kernel.org>
> > ---
> >  include/linux/bpf_verifier.h |  2 +
> >  kernel/bpf/btf.c             | 26 +++++++++++
> >  kernel/bpf/verifier.c        | 89 +++++++++++++++++++++---------------
> >  3 files changed, 79 insertions(+), 38 deletions(-)
> >
> > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > index 3930c963fa67..60d490354397 100644
> > --- a/include/linux/bpf_verifier.h
> > +++ b/include/linux/bpf_verifier.h
> > @@ -548,6 +548,8 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
> >                            u32 regno);
> >  int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
> >                  u32 regno, u32 mem_size);
> > +int check_const_str(struct bpf_verifier_env *env,
> > +                 const struct bpf_reg_state *reg, int regno);
> >
> >  /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
> >  static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 668ecf61649b..6608e8a0c5ca 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6162,6 +6162,23 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> >       return true;
> >  }
> >
> > +static bool btf_param_is_const_str_ptr(const struct btf *btf,
> > +                                    const struct btf_param *param)
> > +{
> > +     const struct btf_type *t;
> > +
> > +     t = btf_type_by_id(btf, param->type);
> > +     if (!btf_type_is_ptr(t))
> > +             return false;
> > +
> > +     t = btf_type_by_id(btf, t->type);
> > +     if (!(BTF_INFO_KIND(t->info) == BTF_KIND_CONST))
> > +             return false;
> > +
>
> Forgot to change this to !=.
>
> > +     t = btf_type_skip_modifiers(btf, t->type, NULL);
> > +     return !strcmp(btf_name_by_offset(btf, t->name_off), "char");
> > +}
> > +
> >  static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> >                                   const struct btf *btf, u32 func_id,
> >                                   struct bpf_reg_state *regs,
> > @@ -6344,6 +6361,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> >               } else if (ptr_to_mem_ok) {
> >                       const struct btf_type *resolve_ret;
> >                       u32 type_size;
> > +                     int err;
> >
> >                       if (is_kfunc) {
> >                               bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
> > @@ -6354,6 +6372,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> >                                * When arg_mem_size is true, the pointer can be
> >                                * void *.
> >                                */
> > +                             if (btf_param_is_const_str_ptr(btf, &args[i])) {
> > +                                     err = check_const_str(env, reg, regno);
> > +                                     if (err < 0)
> > +                                             return err;
> > +                                     i++;
>
> Sorry for not seeing it before, I think this i++ is incorrect. It is skipping
> over the next argument. Which means mem, len pair is not being seen, otherwise
> it should have given an error with the void * argument, because the next
> argument does not have __sz prefix, so there is no mem, len pair in the kfunc
> args.

Thanks for spotting this. Updated my patches, will send v4.

- KP


> The i++ is done for arg_mem_size case because we processed both argno and argno + 1
> together, so the next size arg doesn't need to be processed.
>
> So the bpf_getxattr declaration needs to change from:
>
> noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
>                                      const char *name, void *value, int size)
>
> to
>
> noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
>                                      const char *name, void *value, int value__sz)
>
> You only need the __sz suffix, the part before that is your choice.
> Then it will actually check the size for the value pointer.
> Also, I think neither noinline nor __weak are needed.
>
> > +                                     continue;
> > +                             }
> > +
> >                               if (!btf_type_is_scalar(ref_t) &&
> >                                   !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
> >                                   (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 2859901ffbe3..7ac501122df0 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5840,6 +5840,56 @@ static u32 stack_slot_get_id(struct bpf_verifier_env *env, struct bpf_reg_state
> >       return state->stack[spi].spilled_ptr.id;
> >  }
> >
> > +int check_const_str(struct bpf_verifier_env *env,
> > +                 const struct bpf_reg_state *reg, int regno)
> > +{
> > +     struct bpf_map *map;
> > +     int map_off;
> > +     u64 map_addr;
> > +     char *str_ptr;
> > +     int err;
> > +
> > +     if (reg->type != PTR_TO_MAP_VALUE)
> > +             return -EACCES;
> > +
> > +     map = reg->map_ptr;
> > +     if (!bpf_map_is_rdonly(map)) {
> > +             verbose(env, "R%d does not point to a readonly map'\n", regno);
> > +             return -EACCES;
> > +     }
> > +
> > +     if (!tnum_is_const(reg->var_off)) {
> > +             verbose(env, "R%d is not a constant address'\n", regno);
> > +             return -EACCES;
> > +     }
> > +
> > +     if (!map->ops->map_direct_value_addr) {
> > +             verbose(env,
> > +                     "no direct value access support for this map type\n");
> > +             return -EACCES;
> > +     }
> > +
> > +     err = check_map_access(env, regno, reg->off, map->value_size - reg->off,
> > +                            false, ACCESS_HELPER);
> > +     if (err)
> > +             return err;
> > +
> > +     map_off = reg->off + reg->var_off.value;
> > +     err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
> > +     if (err) {
> > +             verbose(env, "direct value access on string failed\n");
> > +             return err;
> > +     }
> > +
> > +     str_ptr = (char *)(long)(map_addr);
> > +     if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
> > +             verbose(env, "string is not zero-terminated\n");
> > +             return -EINVAL;
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> >  static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> >                         struct bpf_call_arg_meta *meta,
> >                         const struct bpf_func_proto *fn)
> > @@ -6074,44 +6124,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> >                       return err;
> >               err = check_ptr_alignment(env, reg, 0, size, true);
> >       } else if (arg_type == ARG_PTR_TO_CONST_STR) {
> > -             struct bpf_map *map = reg->map_ptr;
> > -             int map_off;
> > -             u64 map_addr;
> > -             char *str_ptr;
> > -
> > -             if (!bpf_map_is_rdonly(map)) {
> > -                     verbose(env, "R%d does not point to a readonly map'\n", regno);
> > -                     return -EACCES;
> > -             }
> > -
> > -             if (!tnum_is_const(reg->var_off)) {
> > -                     verbose(env, "R%d is not a constant address'\n", regno);
> > -                     return -EACCES;
> > -             }
> > -
> > -             if (!map->ops->map_direct_value_addr) {
> > -                     verbose(env, "no direct value access support for this map type\n");
> > -                     return -EACCES;
> > -             }
> > -
> > -             err = check_map_access(env, regno, reg->off,
> > -                                    map->value_size - reg->off, false,
> > -                                    ACCESS_HELPER);
> > -             if (err)
> > -                     return err;
> > -
> > -             map_off = reg->off + reg->var_off.value;
> > -             err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
> > -             if (err) {
> > -                     verbose(env, "direct value access on string failed\n");
> > -                     return err;
> > -             }
> > -
> > -             str_ptr = (char *)(long)(map_addr);
> > -             if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
> > -                     verbose(env, "string is not zero-terminated\n");
> > -                     return -EINVAL;
> > -             }
> > +             err = check_const_str(env, reg, regno);
> >       } else if (arg_type == ARG_PTR_TO_KPTR) {
> >               if (process_kptr_func(env, regno, meta))
> >                       return -EACCES;
> > --
> > 2.37.0.rc0.104.g0611611a94-goog
> >
>
> --
> Kartikeya

Re: [PATCH v3 bpf-next 2/5] bpf: kfunc support for ARG_PTR_TO_CONST_STR

[KP Singh]

On Tue, Jun 21, 2022 at 8:27 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>

[...]

>
> Sorry for not seeing it before, I think this i++ is incorrect. It is skipping
> over the next argument. Which means mem, len pair is not being seen, otherwise
> it should have given an error with the void * argument, because the next
> argument does not have __sz prefix, so there is no mem, len pair in the kfunc
> args.
>
> The i++ is done for arg_mem_size case because we processed both argno and argno + 1
> together, so the next size arg doesn't need to be processed.
>
> So the bpf_getxattr declaration needs to change from:
>
> noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
>                                      const char *name, void *value, int size)
>
> to
>
> noinline __weak ssize_t bpf_getxattr(struct dentry *dentry, struct inode *inode,
>                                      const char *name, void *value, int value__sz)
>
> You only need the __sz suffix, the part before that is your choice.
> Then it will actually check the size for the value pointer.
> Also, I think neither noinline nor __weak are needed.
>

So, yes, I thought about this and you are right, noinline and __weak
are indeed not needed. The compiler will inline the call sites. But there
are no call sites to be inlined in the kernel. So, we are good with just
silencing the compiler warnings