On 11/16/20 3:01 PM, KP Singh wrote:
> From: KP Singh <[email protected]>
>
> 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 <[email protected]>
[...]
> /* 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..4d04fc490a14 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 +52,23 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
> return 0;
> }
>
> +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> +{
This should also reject invalid flags. I'd rather change this helper from RET_VOID
to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
passed in here including zero so it can be extended in future.
> + bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC);
> + return 0;
> +}
> +
> +BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm)
> +
> +const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = {
> + .func = bpf_lsm_set_bprm_opts,
> + .gpl_only = false,
> + .ret_type = RET_VOID,
> + .arg1_type = ARG_PTR_TO_BTF_ID,
> + .arg1_btf_id = &bpf_lsm_set_bprm_opts_btf_ids[0],
> + .arg2_type = ARG_ANYTHING,
> +};
> +
[...]
> >
> > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> > +{
>
> This should also reject invalid flags. I'd rather change this helper from RET_VOID
> to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
> passed in here including zero so it can be extended in future.
Sounds good, I added:
enum {
BPF_LSM_F_BPRM_SECUREEXEC = (1ULL << 0),
+ /* Mask for all the currently supported BPRM options */
+ BPF_LSM_F_BRPM_OPTS_MASK = 0x1ULL,
};
changed the return type to RET_INTEGER as suggested checking for
invalid flags as:
BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
{
+
+ if (flags & !BPF_LSM_F_BRPM_OPTS_MASK)
+ return -EINVAL;
Do let me know if this is okay and I can spin up a v2 with these changes.
- KP
>
> > + bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC);
> > + return 0;
> > +}
> > +
> > +BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm)
> > +
> > +const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = {
> > + .func = bpf_lsm_set_bprm_opts,
> > + .gpl_only = false,
> > + .ret_type = RET_VOID,
> > + .arg1_type = ARG_PTR_TO_BTF_ID,
> > + .arg1_btf_id = &bpf_lsm_set_bprm_opts_btf_ids[0],
> > + .arg2_type = ARG_ANYTHING,
> > +};
> > +
On Mon, Nov 16, 2020 at 2:48 PM KP Singh <[email protected]> wrote:
>
> [...]
>
> > >
> > > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> > > +{
> >
> > This should also reject invalid flags. I'd rather change this helper from RET_VOID
> > to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
> > passed in here including zero so it can be extended in future.
>
> Sounds good, I added:
>
> enum {
> BPF_LSM_F_BPRM_SECUREEXEC = (1ULL << 0),
> + /* Mask for all the currently supported BPRM options */
> + BPF_LSM_F_BRPM_OPTS_MASK = 0x1ULL,
> };
No need to add it to uapi.
Keep it next to the helper in .c file like it's done with other flags.
On Mon, Nov 16, 2020 at 11:48 PM KP Singh <[email protected]> wrote:
>
> [...]
>
> > >
> > > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> > > +{
> >
> > This should also reject invalid flags. I'd rather change this helper from RET_VOID
> > to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
> > passed in here including zero so it can be extended in future.
>
> Sounds good, I added:
>
> enum {
> BPF_LSM_F_BPRM_SECUREEXEC = (1ULL << 0),
> + /* Mask for all the currently supported BPRM options */
> + BPF_LSM_F_BRPM_OPTS_MASK = 0x1ULL,
> };
>
> changed the return type to RET_INTEGER as suggested checking for
> invalid flags as:
>
> BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> {
> +
> + if (flags & !BPF_LSM_F_BRPM_OPTS_MASK)
> + return -EINVAL;
>
> Do let me know if this is okay and I can spin up a v2 with these changes.
Oops this should have been:
if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK)
return -EINVAL;
>
> - KP
>
> >
> > > + bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC);
> > > + return 0;
> > > +}
> > > +
> > > +BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm)
> > > +
> > > +const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = {
> > > + .func = bpf_lsm_set_bprm_opts,
> > > + .gpl_only = false,
> > > + .ret_type = RET_VOID,
> > > + .arg1_type = ARG_PTR_TO_BTF_ID,
> > > + .arg1_btf_id = &bpf_lsm_set_bprm_opts_btf_ids[0],
> > > + .arg2_type = ARG_ANYTHING,
> > > +};
> > > +