On Fri, Sep 23, 2022 at 4:18 PM Song Liu <songliubraving@xxxxxx> wrote:
>
> + Björn Töpel
>
> > On Sep 23, 2022, at 3:00 PM, Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > 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.
>
> Hmm... Yeah, this makes sense. But somehow vmtest doesn't
> show any issue with this. Is there a better way to test this?
test_xdp*.sh should surely trigger it,
but I'm surprised the regular test_run doesn't trigger it.
We call bpf_prog_run_xdp() there.
We've added
if (repeat > 1)
bpf_prog_change_xdp(NULL, prog);
there to reduce test_progs time. Maybe it reduced test coverage too much.
