On Tue, Apr 26, 2022 at 6:11 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Thu, Apr 21, 2022 at 04:07:36PM +0200, Benjamin Tissoires wrote:
> > When using error-injection function through bpf to change the return
> > code, we need to know if the function is sleepable or not.
> >
> > Currently the code assumes that all error-inject functions are sleepable,
> > except for a few selected of them, hardcoded in kernel/bpf/verifier.c
> >
> > Add a new flag to error-inject so we can code that information where the
> > function is declared.
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> >
> > ---
> >
> > new in v4:
> > - another approach would be to define a new kfunc_set, and register
> > it with btf. But in that case, what program type would we use?
> > BPF_PROG_TYPE_UNSPEC?
> > - also note that maybe we should consider all of the functions
> > non-sleepable and only mark some as sleepable. IMO it makes more
> > sense to be more restrictive by default.
>
> I think the approach in this patch is fine.
> We didn't have issues with check_non_sleepable_error_inject() so far,
> so I wouldn't start refactoring it.
OK... though I can't help but thinking that adding a new
error-inject.h enum value is going to be bad, because it's an API
change, and users might not expect NS_ERRNO.
OTOH, if we had a new kfunc_set, we keep the existing error-inject API
in place with all the variants and we just teach the verifier that the
function is non sleepable.
>
> > ---
> > include/asm-generic/error-injection.h | 1 +
> > kernel/bpf/verifier.c | 10 ++++++++--
> > lib/error-inject.c | 2 ++
> > 3 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/asm-generic/error-injection.h b/include/asm-generic/error-injection.h
> > index fbca56bd9cbc..5974942353a6 100644
> > --- a/include/asm-generic/error-injection.h
> > +++ b/include/asm-generic/error-injection.h
> > @@ -9,6 +9,7 @@ enum {
> > EI_ETYPE_ERRNO, /* Return -ERRNO if failure */
> > EI_ETYPE_ERRNO_NULL, /* Return -ERRNO or NULL if failure */
> > EI_ETYPE_TRUE, /* Return true if failure */
> > + EI_ETYPE_NS_ERRNO, /* Return -ERRNO if failure and tag the function as non-sleepable */
>
> > };
> >
> > struct error_injection_entry {
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 0f339f9058f3..45c8feea6478 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -14085,6 +14085,11 @@ static int check_non_sleepable_error_inject(u32 btf_id)
> > return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
> > }
> >
> > +static int is_non_sleepable_error_inject(unsigned long addr)
> > +{
> > + return get_injectable_error_type(addr) == EI_ETYPE_NS_ERRNO;
>
> It's a linear search. Probably ok. But would be good to double check
> that we're not calling it a lot.
IIUC, the kfunc_set approach would solve that, no?
Cheers,
Benjamin
>
> > +}
> > +
> > int bpf_check_attach_target(struct bpf_verifier_log *log,
> > const struct bpf_prog *prog,
> > const struct bpf_prog *tgt_prog,
> > @@ -14281,8 +14286,9 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
> > /* fentry/fexit/fmod_ret progs can be sleepable only if they are
> > * attached to ALLOW_ERROR_INJECTION and are not in denylist.
> > */
> > - if (!check_non_sleepable_error_inject(btf_id) &&
> > - within_error_injection_list(addr))
> > + if (within_error_injection_list(addr) &&
> > + !check_non_sleepable_error_inject(btf_id) &&
> > + !is_non_sleepable_error_inject(addr))
> > ret = 0;
> > break;
> > case BPF_PROG_TYPE_LSM:
> > diff --git a/lib/error-inject.c b/lib/error-inject.c
> > index 2ff5ef689d72..560c3b18f439 100644
> > --- a/lib/error-inject.c
> > +++ b/lib/error-inject.c
> > @@ -183,6 +183,8 @@ static const char *error_type_string(int etype)
> > return "ERRNO_NULL";
> > case EI_ETYPE_TRUE:
> > return "TRUE";
> > + case EI_ETYPE_NS_ERRNO:
> > + return "NS_ERRNO";
> > default:
> > return "(unknown)";
> > }
> > --
> > 2.35.1
> >
>
