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sched_ext: Replace set_arg_maybe_null() with __nullable CFI stub tags

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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>
This commit is contained in:
Tejun Heo 2024-10-24 06:58:09 -10:00
parent cf583264d0
commit b7d0bbcf0c
1 changed files with 2 additions and 64 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

66
kernel/sched/ext.c
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@ -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) {}