Commit b7d0bbcf authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Acked-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent cf583264

kernel/sched/ext.c

+2 −64
Original line number Diff line number Diff line
@@ -5407,67 +5407,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link) 
#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) {}