[PATCH bpf-next 4/8] bpf: Add helpers for trampoline image management

Song Liu
2023-09-20T05:32:23Z

As BPF trampoline of different archs moves from bpf_jit_[alloc|free]_exec()
to bpf_prog_pack_[alloc|free](), we need to use different _alloc, _free for
different archs during the transition. Add the following helpers for this
transition:

void *arch_alloc_bpf_trampoline(int size);
void arch_free_bpf_trampoline(void *image, int size);
void arch_protect_bpf_trampoline(void *image, int size);
void arch_unprotect_bpf_trampoline(void *image, int size);

The fallback version of these helpers require size <= PAGE_SIZE, but they
are only called with size == PAGE_SIZE. They will be called with size <
PAGE_SIZE when arch_bpf_trampoline_size() helper is introduced later.

Signed-off-by: Song Liu <song@kernel.org>
---
include/linux/bpf.h | 5 +++++
kernel/bpf/bpf_struct_ops.c | 12 +++++-----
kernel/bpf/trampoline.c | 44 +++++++++++++++++++++++++++++++------
3 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 27a18c0c10ca..548f3ef34ba1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1083,6 +1083,11 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
const struct btf_func_model *m, u32 flags,
struct bpf_tramp_links *tlinks,
void *func_addr);
+void *arch_alloc_bpf_trampoline(int size);
+void arch_free_bpf_trampoline(void *image, int size);
+void arch_protect_bpf_trampoline(void *image, int size);
+void arch_unprotect_bpf_trampoline(void *image, int size);
+
u64 notrace __bpf_prog_enter_sleepable_recur(struct bpf_prog *prog,
struct bpf_tramp_run_ctx *run_ctx);
void notrace __bpf_prog_exit_sleepable_recur(struct bpf_prog *prog, u64 start,
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index db6176fb64dc..e9e95879bce2 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -515,7 +515,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
if (err)
goto reset_unlock;
}
- set_memory_rox((long)st_map->image, 1);
+ arch_protect_bpf_trampoline(st_map->image, PAGE_SIZE);
/* Let bpf_link handle registration & unregistration.
*
* Pair with smp_load_acquire() during lookup_elem().
@@ -524,7 +524,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
goto unlock;
}

- set_memory_rox((long)st_map->image, 1);
+ arch_protect_bpf_trampoline(st_map->image, PAGE_SIZE);
err = st_ops->reg(kdata);
if (likely(!err)) {
/* This refcnt increment on the map here after
@@ -547,8 +547,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
* there was a race in registering the struct_ops (under the same name) to
* a sub-system through different struct_ops's maps.
*/
- set_memory_nx((long)st_map->image, 1);
- set_memory_rw((long)st_map->image, 1);
+ arch_unprotect_bpf_trampoline(st_map->image, PAGE_SIZE);

reset_unlock:
bpf_struct_ops_map_put_progs(st_map);
@@ -616,7 +615,7 @@ static void __bpf_struct_ops_map_free(struct bpf_map *map)
bpf_struct_ops_map_put_progs(st_map);
bpf_map_area_free(st_map->links);
if (st_map->image) {
- bpf_jit_free_exec(st_map->image);
+ arch_free_bpf_trampoline(st_map->image, PAGE_SIZE);
bpf_jit_uncharge_modmem(PAGE_SIZE);
}
bpf_map_area_free(st_map->uvalue);
@@ -691,7 +690,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
return ERR_PTR(ret);
}

- st_map->image = bpf_jit_alloc_exec(PAGE_SIZE);
+ st_map->image = arch_alloc_bpf_trampoline(PAGE_SIZE);
if (!st_map->image) {
/* __bpf_struct_ops_map_free() uses st_map->image as flag
* for "charged or not". In this case, we need to unchange
@@ -711,7 +710,6 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
}

mutex_init(&st_map->lock);
- set_vm_flush_reset_perms(st_map->image);
bpf_map_init_from_attr(map, attr);

return map;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index e114a1c7961e..5509bdf98067 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -254,7 +254,7 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_a
static void bpf_tramp_image_free(struct bpf_tramp_image *im)
{
bpf_image_ksym_del(&im->ksym);
- bpf_jit_free_exec(im->image);
+ arch_free_bpf_trampoline(im->image, PAGE_SIZE);
bpf_jit_uncharge_modmem(PAGE_SIZE);
percpu_ref_exit(&im->pcref);
kfree_rcu(im, rcu);
@@ -365,10 +365,9 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key)
goto out_free_im;

err = -ENOMEM;
- im->image = image = bpf_jit_alloc_exec(PAGE_SIZE);
+ im->image = image = arch_alloc_bpf_trampoline(PAGE_SIZE);
if (!image)
goto out_uncharge;
- set_vm_flush_reset_perms(image);

err = percpu_ref_init(&im->pcref, __bpf_tramp_image_release, 0, GFP_KERNEL);
if (err)
@@ -381,7 +380,7 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key)
return im;

out_free_image:
- bpf_jit_free_exec(im->image);
+ arch_free_bpf_trampoline(im->image, PAGE_SIZE);
out_uncharge:
bpf_jit_uncharge_modmem(PAGE_SIZE);
out_free_im:
@@ -444,7 +443,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
if (err < 0)
goto out_free;

- set_memory_rox((long)im->image, 1);
+ arch_protect_bpf_trampoline(im->image, PAGE_SIZE);

WARN_ON(tr->cur_image && total == 0);
if (tr->cur_image)
@@ -465,8 +464,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
tr->fops->trampoline = 0;

/* reset im->image memory attr for arch_prepare_bpf_trampoline */
- set_memory_nx((long)im->image, 1);
- set_memory_rw((long)im->image, 1);
+ arch_unprotect_bpf_trampoline(im->image, PAGE_SIZE);
goto again;
}
#endif
@@ -1040,6 +1038,38 @@ arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image
return -ENOTSUPP;
}

+void * __weak arch_alloc_bpf_trampoline(int size)
+{
+ void *image;
+
+ WARN_ON_ONCE(size > PAGE_SIZE || size <= 0);
+ image = bpf_jit_alloc_exec(PAGE_SIZE);
+ if (image)
+ set_vm_flush_reset_perms(image);
+ return image;
+}
+
+void __weak arch_free_bpf_trampoline(void *image, int size)
+{
+ /* bpf_jit_free_exec doesn't need "size", but
+ * bpf_prog_pack_free() needs it.
+ */
+ bpf_jit_free_exec(image);
+}
+
+void __weak arch_protect_bpf_trampoline(void *image, int size)
+{
+ WARN_ON_ONCE(size > PAGE_SIZE || size <= 0);
+ set_memory_rox((long)image, 1);
+}
+
+void __weak arch_unprotect_bpf_trampoline(void *image, int size)
+{
+ WARN_ON_ONCE(size > PAGE_SIZE || size <= 0);
+ set_memory_nx((long)image, 1);
+ set_memory_rw((long)image, 1);
+}
+
static int __init init_trampolines(void)
{
int i;
--
2.34.1