diff mbox series

[bpf-next,v3,1/2] bpf: Add bpf_lsm_set_bprm_opts helper

Message ID 20201117021307.1846300-1-kpsingh@chromium.org (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series [bpf-next,v3,1/2] bpf: Add bpf_lsm_set_bprm_opts helper | expand

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Commit Message

KP Singh Nov. 17, 2020, 2:13 a.m. UTC 
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       | 18 ++++++++++++++++++
 kernel/bpf/bpf_lsm.c           | 27 +++++++++++++++++++++++++++
 scripts/bpf_helpers_doc.py     |  2 ++
 tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++
 4 files changed, 65 insertions(+)

Comments

Martin KaFai Lau Nov. 17, 2020, 6:14 a.m. UTC | #1 
On Tue, Nov 17, 2020 at 02:13:06AM +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>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Daniel Borkmann Nov. 17, 2020, 10:41 p.m. UTC | #2 
On 11/17/20 3:13 AM, 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       | 18 ++++++++++++++++++
>   kernel/bpf/bpf_lsm.c           | 27 +++++++++++++++++++++++++++
>   scripts/bpf_helpers_doc.py     |  2 ++
>   tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++
>   4 files changed, 65 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 162999b12790..bfa79054d106 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3787,6 +3787,18 @@ 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)
> + *

small nit: should have no extra newline (same for the tools/ copy)

> + *	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 cleared if the flag is not specified.
> + *	Return
> + *		**-EINVAL** if invalid *flags* are passed.
> + *
>    */
>   #define __BPF_FUNC_MAPPER(FN)		\
>   	FN(unspec),			\
> @@ -3948,6 +3960,7 @@ 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 +4132,11 @@ 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..cd85482228a0 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	BPF_LSM_F_BPRM_SECUREEXEC
> +
> +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> +{
> +

ditto

Would have fixed up these things on the fly while applying, but one small item
I wanted to bring up here given uapi which will then freeze: it would be cleaner
to call the helper just bpf_bprm_opts_set() or so given it's implied that we
attach to lsm here and we don't use _lsm in the naming for the others either.
Similarly, I'd drop the _LSM from the flag/mask.

> +	if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK)
> +		return -EINVAL;
> +
> +	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_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_BTF_ID,
> +	.arg1_btf_id	= &bpf_lsm_set_bprm_opts_btf_ids[0],
> +	.arg2_type	= ARG_ANYTHING,
> +};
> +
>   static const struct bpf_func_proto *
>   bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   {
> @@ -71,6 +96,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   		return &bpf_task_storage_get_proto;
>   	case BPF_FUNC_task_storage_delete:
>   		return &bpf_task_storage_delete_proto;
> +	case BPF_FUNC_lsm_set_bprm_opts:
> +		return &bpf_lsm_set_bprm_opts_proto;
>   	default:
>   		return tracing_prog_func_proto(func_id, prog);
>   	}
KP Singh Nov. 17, 2020, 11:35 p.m. UTC | #3 
On Tue, Nov 17, 2020 at 11:41 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 11/17/20 3:13 AM, 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       | 18 ++++++++++++++++++
> >   kernel/bpf/bpf_lsm.c           | 27 +++++++++++++++++++++++++++
> >   scripts/bpf_helpers_doc.py     |  2 ++
> >   tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++
> >   4 files changed, 65 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 162999b12790..bfa79054d106 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3787,6 +3787,18 @@ 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)
> > + *
>
> small nit: should have no extra newline (same for the tools/ copy)
>
> > + *   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 cleared if the flag is not specified.
> > + *   Return
> > + *           **-EINVAL** if invalid *flags* are passed.
> > + *
> >    */
> >   #define __BPF_FUNC_MAPPER(FN)               \
> >       FN(unspec),                     \
> > @@ -3948,6 +3960,7 @@ 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 +4132,11 @@ 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..cd85482228a0 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     BPF_LSM_F_BPRM_SECUREEXEC
> > +
> > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> > +{
> > +
>
> ditto
>
> Would have fixed up these things on the fly while applying, but one small item
> I wanted to bring up here given uapi which will then freeze: it would be cleaner
> to call the helper just bpf_bprm_opts_set() or so given it's implied that we
> attach to lsm here and we don't use _lsm in the naming for the others either.
> Similarly, I'd drop the _LSM from the flag/mask.
>

Thanks Daniel, this makes sense and is more future proof, I respun this and
sent out another version with some minor fixes and the rename. Also added
Martin's acks.

- KP
diff mbox series

Patch

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 162999b12790..bfa79054d106 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3787,6 +3787,18 @@  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
+ *		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 cleared if the flag is not specified.
+ *	Return
+ *		**-EINVAL** if invalid *flags* are passed.
+ *
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3960,7 @@  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 +4132,11 @@  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..cd85482228a0 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	BPF_LSM_F_BPRM_SECUREEXEC
+
+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);
+	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_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &bpf_lsm_set_bprm_opts_btf_ids[0],
+	.arg2_type	= ARG_ANYTHING,
+};
+
 static const struct bpf_func_proto *
 bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -71,6 +96,8 @@  bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_task_storage_get_proto;
 	case BPF_FUNC_task_storage_delete:
 		return &bpf_task_storage_delete_proto;
+	case BPF_FUNC_lsm_set_bprm_opts:
+		return &bpf_lsm_set_bprm_opts_proto;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 31484377b8b1..c5bc947a70ad 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -418,6 +418,7 @@  class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
@@ -465,6 +466,7 @@  class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 162999b12790..bfa79054d106 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3787,6 +3787,18 @@  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
+ *		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 cleared if the flag is not specified.
+ *	Return
+ *		**-EINVAL** if invalid *flags* are passed.
+ *
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3960,7 @@  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 +4132,11 @@  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;			\