sched_ext: Replace set_arg_maybe_null() with __nullable CFI stub tags

ops.dispatch() and ops.yield() may be fed a NULL task_struct pointer.
set_arg_maybe_null() is used to tell the verifier that they should be NULL
checked before being dereferenced. BPF now has an a lot prettier way to
express this - tagging arguments in CFI stubs with __nullable. Replace
set_arg_maybe_null() with __nullable CFI stub tags.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 00a05578d75a86a7bf6079863a4e3ea87635ec8b..6705c2e67c9939326d3b420660fc318811458008 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5407,67 +5407,8 @@ err_disable:
 #include <linux/bpf.h>
 #include <linux/btf.h>
 
-extern struct btf *btf_vmlinux;
 static const struct btf_type *task_struct_type;
 
-static bool set_arg_maybe_null(const char *op, int arg_n, int off, int size,
-                              enum bpf_access_type type,
-                              const struct bpf_prog *prog,
-                              struct bpf_insn_access_aux *info)
-{
-       struct btf *btf = bpf_get_btf_vmlinux();
-       const struct bpf_struct_ops_desc *st_ops_desc;
-       const struct btf_member *member;
-       const struct btf_type *t;
-       u32 btf_id, member_idx;
-       const char *mname;
-
-       /* struct_ops op args are all sequential, 64-bit numbers */
-       if (off != arg_n * sizeof(__u64))
-               return false;
-
-       /* btf_id should be the type id of struct sched_ext_ops */
-       btf_id = prog->aux->attach_btf_id;
-       st_ops_desc = bpf_struct_ops_find(btf, btf_id);
-       if (!st_ops_desc)
-               return false;
-
-       /* BTF type of struct sched_ext_ops */
-       t = st_ops_desc->type;
-
-       member_idx = prog->expected_attach_type;
-       if (member_idx >= btf_type_vlen(t))
-               return false;
-
-       /*
-        * Get the member name of this struct_ops program, which corresponds to
-        * a field in struct sched_ext_ops. For example, the member name of the
-        * dispatch struct_ops program (callback) is "dispatch".
-        */
-       member = &btf_type_member(t)[member_idx];
-       mname = btf_name_by_offset(btf_vmlinux, member->name_off);
-
-       if (!strcmp(mname, op)) {
-               /*
-                * The value is a pointer to a type (struct task_struct) given
-                * by a BTF ID (PTR_TO_BTF_ID). It is trusted (PTR_TRUSTED),
-                * however, can be a NULL (PTR_MAYBE_NULL). The BPF program
-                * should check the pointer to make sure it is not NULL before
-                * using it, or the verifier will reject the program.
-                *
-                * Longer term, this is something that should be addressed by
-                * BTF, and be fully contained within the verifier.
-                */
-               info->reg_type = PTR_MAYBE_NULL | PTR_TO_BTF_ID | PTR_TRUSTED;
-               info->btf = btf_vmlinux;
-               info->btf_id = btf_tracing_ids[BTF_TRACING_TYPE_TASK];
-
-               return true;
-       }
-
-       return false;
-}
-
 static bool bpf_scx_is_valid_access(int off, int size,
                                    enum bpf_access_type type,
                                    const struct bpf_prog *prog,
@@ -5475,9 +5416,6 @@ static bool bpf_scx_is_valid_access(int off, int size,
 {
        if (type != BPF_READ)
                return false;
-       if (set_arg_maybe_null("dispatch", 1, off, size, type, prog, info) ||
-           set_arg_maybe_null("yield", 1, off, size, type, prog, info))
-               return true;
        if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS)
                return false;
        if (off % size != 0)
@@ -5637,13 +5575,13 @@ static int bpf_scx_validate(void *kdata)
 static s32 sched_ext_ops__select_cpu(struct task_struct *p, s32 prev_cpu, u64 wake_flags) { return -EINVAL; }
 static void sched_ext_ops__enqueue(struct task_struct *p, u64 enq_flags) {}
 static void sched_ext_ops__dequeue(struct task_struct *p, u64 enq_flags) {}
-static void sched_ext_ops__dispatch(s32 prev_cpu, struct task_struct *p) {}
+static void sched_ext_ops__dispatch(s32 prev_cpu, struct task_struct *prev__nullable) {}
 static void sched_ext_ops__tick(struct task_struct *p) {}
 static void sched_ext_ops__runnable(struct task_struct *p, u64 enq_flags) {}
 static void sched_ext_ops__running(struct task_struct *p) {}
 static void sched_ext_ops__stopping(struct task_struct *p, bool runnable) {}
 static void sched_ext_ops__quiescent(struct task_struct *p, u64 deq_flags) {}
-static bool sched_ext_ops__yield(struct task_struct *from, struct task_struct *to) { return false; }
+static bool sched_ext_ops__yield(struct task_struct *from, struct task_struct *to__nullable) { return false; }
 static bool sched_ext_ops__core_sched_before(struct task_struct *a, struct task_struct *b) { return false; }
 static void sched_ext_ops__set_weight(struct task_struct *p, u32 weight) {}
 static void sched_ext_ops__set_cpumask(struct task_struct *p, const struct cpumask *mask) {}