On Tue, Mar 3, 2020 at 6:12 AM KP Singh <kpsingh@xxxxxxxxxxxx> wrote: > > From: KP Singh <kpsingh@xxxxxxxxxx> > > - Functions that are whitlisted by for error injection i.e. > within_error_injection_list. > - Security hooks, this is expected to be cleaned up after the KRSI > patches introduce the LSM_HOOK macro: > > https://lore.kernel.org/bpf/20200220175250.10795-1-kpsingh@xxxxxxxxxxxx/ Commit message can use a bit more work for sure. Why (and even what) of the changes is not really explained well. > > - The attachment is currently limited to functions that return an int. > This can be extended later other types (e.g. PTR). > > Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx> > --- > kernel/bpf/btf.c | 28 ++++++++++++++++++++-------- > kernel/bpf/verifier.c | 31 +++++++++++++++++++++++++++++++ > 2 files changed, 51 insertions(+), 8 deletions(-) > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index 30841fb8b3c0..50080add2ab9 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -3710,14 +3710,26 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, > nr_args--; > } > > - if ((prog->expected_attach_type == BPF_TRACE_FEXIT || > - prog->expected_attach_type == BPF_MODIFY_RETURN) && > - arg == nr_args) { > - if (!t) > - /* Default prog with 5 args. 6th arg is retval. */ > - return true; > - /* function return type */ > - t = btf_type_by_id(btf, t->type); > + if (arg == nr_args) { > + if (prog->expected_attach_type == BPF_TRACE_FEXIT) { > + if (!t) > + return true; > + t = btf_type_by_id(btf, t->type); > + } else if (prog->expected_attach_type == BPF_MODIFY_RETURN) { > + /* For now the BPF_MODIFY_RETURN can only be attached to > + * functions that return an int. > + */ > + if (!t) > + return false; > + > + t = btf_type_skip_modifiers(btf, t->type, NULL); > + if (!btf_type_is_int(t)) { Should the size of int be verified here? E.g., if some function returns u8, is that ok for BPF program to return, say, (1<<30) ? > + bpf_log(log, > + "ret type %s not allowed for fmod_ret\n", > + btf_kind_str[BTF_INFO_KIND(t->info)]); > + return false; > + } > + } > } else if (arg >= nr_args) { > bpf_log(log, "func '%s' doesn't have %d-th argument\n", > tname, arg + 1); > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 2460c8e6b5be..ae32517d4ccd 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -19,6 +19,7 @@ > #include <linux/sort.h> > #include <linux/perf_event.h> > #include <linux/ctype.h> > +#include <linux/error-injection.h> > > #include "disasm.h" > > @@ -9800,6 +9801,33 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env) > > return 0; > } > +#define SECURITY_PREFIX "security_" > + > +static int check_attach_modify_return(struct bpf_verifier_env *env) > +{ > + struct bpf_prog *prog = env->prog; > + unsigned long addr = (unsigned long) prog->aux->trampoline->func.addr; > + > + if (within_error_injection_list(addr)) > + return 0; > + > + /* This is expected to be cleaned up in the future with the KRSI effort > + * introducing the LSM_HOOK macro for cleaning up lsm_hooks.h. > + */ > + if (!strncmp(SECURITY_PREFIX, prog->aux->attach_func_name, > + sizeof(SECURITY_PREFIX) - 1)) { > + > + if (!capable(CAP_MAC_ADMIN)) > + return -EPERM; > + > + return 0; > + } > + > + verbose(env, "fmod_ret attach_btf_id %u (%s) is not modifiable\n", > + prog->aux->attach_btf_id, prog->aux->attach_func_name); > + > + return -EINVAL; > +} > > static int check_attach_btf_id(struct bpf_verifier_env *env) > { > @@ -10000,6 +10028,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) > } > tr->func.addr = (void *)addr; > prog->aux->trampoline = tr; > + > + if (prog->expected_attach_type == BPF_MODIFY_RETURN) > + ret = check_attach_modify_return(env); > out: > mutex_unlock(&tr->mutex); > if (ret) > -- > 2.20.1 >
