Messages in this thread | | | From | KP Singh <> | Date | Tue, 17 Nov 2020 03:07:11 +0100 | Subject | Re: [PATCH bpf-next v2 1/2] bpf: Add bpf_lsm_set_bprm_opts helper |
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On Tue, Nov 17, 2020 at 3:03 AM KP Singh <kpsingh@chromium.org> wrote: > > On Tue, Nov 17, 2020 at 1:11 AM Martin KaFai Lau <kafai@fb.com> wrote: > > > > On Mon, Nov 16, 2020 at 11:25:35PM +0000, KP Singh wrote: > > > From: KP Singh <kpsingh@google.com> > > > > > > The helper allows modification of certain bits on the linux_binprm > > > struct starting with the secureexec bit which can be updated using the > > > BPF_LSM_F_BPRM_SECUREEXEC flag. > > > > > > secureexec can be set by the LSM for privilege gaining executions to set > > > the AT_SECURE auxv for glibc. When set, the dynamic linker disables the > > > use of certain environment variables (like LD_PRELOAD). > > > > > > Signed-off-by: KP Singh <kpsingh@google.com> > > > --- > > > include/uapi/linux/bpf.h | 14 ++++++++++++++ > > > kernel/bpf/bpf_lsm.c | 27 +++++++++++++++++++++++++++ > > > scripts/bpf_helpers_doc.py | 2 ++ > > > tools/include/uapi/linux/bpf.h | 14 ++++++++++++++ > > > 4 files changed, 57 insertions(+) > > > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > > index 162999b12790..7f1b6ba8246c 100644 > > > --- a/include/uapi/linux/bpf.h > > > +++ b/include/uapi/linux/bpf.h > > > @@ -3787,6 +3787,14 @@ union bpf_attr { > > > * *ARG_PTR_TO_BTF_ID* of type *task_struct*. > > > * Return > > > * Pointer to the current task. > > > + * > > > + * long bpf_lsm_set_bprm_opts(struct linux_binprm *bprm, u64 flags) > > > + * > > > + * Description > > > + * Sets certain options on the *bprm*: > > > + * > > > + * **BPF_LSM_F_BPRM_SECUREEXEC** Set the secureexec bit > > > + * which sets the **AT_SECURE** auxv for glibc. > > The return value needs to be documented also. > > Done. > > > > > > */ > > > #define __BPF_FUNC_MAPPER(FN) \ > > > FN(unspec), \ > > > @@ -3948,6 +3956,7 @@ union bpf_attr { > > > FN(task_storage_get), \ > > > FN(task_storage_delete), \ > > > FN(get_current_task_btf), \ > > > + FN(lsm_set_bprm_opts), \ > > > /* */ > > > > > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > > > @@ -4119,6 +4128,11 @@ enum bpf_lwt_encap_mode { > > > BPF_LWT_ENCAP_IP, > > > }; > > > > > > +/* Flags for LSM helpers */ > > > +enum { > > > + BPF_LSM_F_BPRM_SECUREEXEC = (1ULL << 0), > > > +}; > > > + > > > #define __bpf_md_ptr(type, name) \ > > > union { \ > > > type name; \ > > > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c > > > index 553107f4706a..31f85474a0ef 100644 > > > --- a/kernel/bpf/bpf_lsm.c > > > +++ b/kernel/bpf/bpf_lsm.c > > > @@ -7,6 +7,7 @@ > > > #include <linux/filter.h> > > > #include <linux/bpf.h> > > > #include <linux/btf.h> > > > +#include <linux/binfmts.h> > > > #include <linux/lsm_hooks.h> > > > #include <linux/bpf_lsm.h> > > > #include <linux/kallsyms.h> > > > @@ -51,6 +52,30 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, > > > return 0; > > > } > > > > > > +/* Mask for all the currently supported BPRM option flags */ > > > +#define BPF_LSM_F_BRPM_OPTS_MASK 0x1ULL > > If there is a need to have v3, it will be better to use > > BPF_LSM_F_BPRM_SECUREEXEC instead of 0x1ULL. > > Done. > > > > > > + > > > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags) > > > +{ > > > + > > > + if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK) > > > + return -EINVAL; > > > + > > > + bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC); > > The intention of this helper is to set "or clear" a bit? > > It may be useful to clarify the "clear" part in the doc also. > > Updated the docs: > > * long bpf_lsm_set_bprm_opts(struct linux_binprm *bprm, u64 flags) > * > * Description > * Set or clear certain options on *bprm*: > * > * **BPF_LSM_F_BPRM_SECUREEXEC** Set the secureexec bit > * which sets the **AT_SECURE** auxv for glibc. The bit is > * is cleared if the flag is not specified.
(-is) = cleared if the flag is not specified. (Thanks checkpatch!)
> * Return > * **-EINVAL** if invalid *flags* are passed. > > > > > > + return 0; > > > +} > > > +
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