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.
> ---
> 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.
> +}
> +
> 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
>
