On Fri, Sep 23, 2022 at 2:18 PM Song Liu <song@xxxxxxxxxx> wrote:
>
> Allocate bpf_dispatcher with bpf_prog_pack_alloc so that bpf_dispatcher
> can share pages with bpf programs.
>
> This also fixes CPA W^X warnning like:
>
> CPA refuse W^X violation: 8000000000000163 -> 0000000000000163 range: ...
>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
> ---
> include/linux/bpf.h | 1 +
> include/linux/filter.h | 5 +++++
> kernel/bpf/core.c | 9 +++++++--
> kernel/bpf/dispatcher.c | 21 ++++++++++++++++++---
> 4 files changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index edd43edb27d6..a8d0cfe14372 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -946,6 +946,7 @@ struct bpf_dispatcher {
> struct bpf_dispatcher_prog progs[BPF_DISPATCHER_MAX];
> int num_progs;
> void *image;
> + void *rw_image;
> u32 image_off;
> struct bpf_ksym ksym;
> };
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 98e28126c24b..efc42a6e3aed 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1023,6 +1023,8 @@ extern long bpf_jit_limit_max;
>
> typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);
>
> +void bpf_jit_fill_hole_with_zero(void *area, unsigned int size);
> +
> struct bpf_binary_header *
> bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
> unsigned int alignment,
> @@ -1035,6 +1037,9 @@ void bpf_jit_free(struct bpf_prog *fp);
> struct bpf_binary_header *
> bpf_jit_binary_pack_hdr(const struct bpf_prog *fp);
>
> +void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns);
> +void bpf_prog_pack_free(struct bpf_binary_header *hdr);
> +
> static inline bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp)
> {
> return list_empty(&fp->aux->ksym.lnode) ||
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index d1be78c28619..711fd293b6de 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -825,6 +825,11 @@ struct bpf_prog_pack {
> unsigned long bitmap[];
> };
>
> +void bpf_jit_fill_hole_with_zero(void *area, unsigned int size)
> +{
> + memset(area, 0, size);
> +}
> +
> #define BPF_PROG_SIZE_TO_NBITS(size) (round_up(size, BPF_PROG_CHUNK_SIZE) / BPF_PROG_CHUNK_SIZE)
>
> static DEFINE_MUTEX(pack_mutex);
> @@ -864,7 +869,7 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
> return pack;
> }
>
> -static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
> +void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
> {
> unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size);
> struct bpf_prog_pack *pack;
> @@ -905,7 +910,7 @@ static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insn
> return ptr;
> }
>
> -static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
> +void bpf_prog_pack_free(struct bpf_binary_header *hdr)
> {
> struct bpf_prog_pack *pack = NULL, *tmp;
> unsigned int nbits;
> diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
> index 2444bd15cc2d..8a10300854b6 100644
> --- a/kernel/bpf/dispatcher.c
> +++ b/kernel/bpf/dispatcher.c
> @@ -104,7 +104,7 @@ static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image)
>
> static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
> {
> - void *old, *new;
> + void *old, *new, *tmp;
> u32 noff;
> int err;
>
> @@ -117,8 +117,14 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
> }
>
> new = d->num_progs ? d->image + noff : NULL;
> + tmp = d->num_progs ? d->rw_image + noff : NULL;
> if (new) {
> - if (bpf_dispatcher_prepare(d, new))
> + /* Prepare the dispatcher in d->rw_image. Then use
> + * bpf_arch_text_copy to update d->image, which is RO+X.
> + */
> + if (bpf_dispatcher_prepare(d, tmp))
> + return;
> + if (IS_ERR(bpf_arch_text_copy(new, tmp, PAGE_SIZE / 2)))
I don't think we can create a dispatcher with one ip
and then copy over into a different location.
See emit_bpf_dispatcher() -> emit_cond_near_jump()
It's a relative offset jump.
