From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com References: <20160914072415.26021-1-mic@digikod.net> <20160914072415.26021-4-mic@digikod.net> <20160914185157.GA53542@ast-mbp.thefacebook.com> <57D9DBC9.2010605@digikod.net> <20160914232815.GE60248@ast-mbp.thefacebook.com> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Message-ID: <57DB17E8.9000509@digikod.net> Date: Thu, 15 Sep 2016 23:51:36 +0200 MIME-Version: 1.0 In-Reply-To: <20160914232815.GE60248@ast-mbp.thefacebook.com> Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="WLFibjtnJnf4cBIdDsaD4hMorTSFrVv4s" Subject: [kernel-hardening] Re: [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles To: Alexei Starovoitov Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Daniel Borkmann , Daniel Mack , David Drysdale , "David S . Miller" , Elena Reshetova , "Eric W . Biederman" , James Morris , Kees Cook , Paul Moore , Sargun Dhillon , "Serge E . Hallyn" , Tejun Heo , Will Drewry , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, cgroups@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --WLFibjtnJnf4cBIdDsaD4hMorTSFrVv4s Content-Type: multipart/mixed; boundary="wICN1dhgOea8bvfdPU4X9ikMbRRDF9btV"; protected-headers="v1" From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= To: Alexei Starovoitov Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Daniel Borkmann , Daniel Mack , David Drysdale , "David S . Miller" , Elena Reshetova , "Eric W . Biederman" , James Morris , Kees Cook , Paul Moore , Sargun Dhillon , "Serge E . Hallyn" , Tejun Heo , Will Drewry , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, cgroups@vger.kernel.org Message-ID: <57DB17E8.9000509@digikod.net> Subject: Re: [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles References: <20160914072415.26021-1-mic@digikod.net> <20160914072415.26021-4-mic@digikod.net> <20160914185157.GA53542@ast-mbp.thefacebook.com> <57D9DBC9.2010605@digikod.net> <20160914232815.GE60248@ast-mbp.thefacebook.com> In-Reply-To: <20160914232815.GE60248@ast-mbp.thefacebook.com> --wICN1dhgOea8bvfdPU4X9ikMbRRDF9btV Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 15/09/2016 01:28, Alexei Starovoitov wrote: > On Thu, Sep 15, 2016 at 01:22:49AM +0200, Micka=EBl Sala=FCn wrote: >> >> On 14/09/2016 20:51, Alexei Starovoitov wrote: >>> On Wed, Sep 14, 2016 at 09:23:56AM +0200, Micka=EBl Sala=FCn wrote: >>>> This new arraymap looks like a set and brings new properties: >>>> * strong typing of entries: the eBPF functions get the array type of= >>>> elements instead of CONST_PTR_TO_MAP (e.g. >>>> CONST_PTR_TO_LANDLOCK_HANDLE_FS); >>>> * force sequential filling (i.e. replace or append-only update), whi= ch >>>> allow quick browsing of all entries. >>>> >>>> This strong typing is useful to statically check if the content of a= map >>>> can be passed to an eBPF function. For example, Landlock use it to s= tore >>>> and manage kernel objects (e.g. struct file) instead of dealing with= >>>> userland raw data. This improve efficiency and ensure that an eBPF >>>> program can only call functions with the right high-level arguments.= >>>> >>>> The enum bpf_map_handle_type list low-level types (e.g. >>>> BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) which are identified when >>>> updating a map entry (handle). This handle types are used to infer a= >>>> high-level arraymap type which are listed in enum bpf_map_array_type= >>>> (e.g. BPF_MAP_ARRAY_TYPE_LANDLOCK_FS). >>>> >>>> For now, this new arraymap is only used by Landlock LSM (cf. next >>>> commits) but it could be useful for other needs. >>>> >>>> Changes since v2: >>>> * add a RLIMIT_NOFILE-based limit to the maximum number of arraymap >>>> handle entries (suggested by Andy Lutomirski) >>>> * remove useless checks >>>> >>>> Changes since v1: >>>> * arraymap of handles replace custom checker groups >>>> * simpler userland API >>>> >>>> Signed-off-by: Micka=EBl Sala=FCn >>>> Cc: Alexei Starovoitov >>>> Cc: Andy Lutomirski >>>> Cc: Daniel Borkmann >>>> Cc: David S. Miller >>>> Cc: Kees Cook >>>> Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEX= h77FD2G5o71yD7g@mail.gmail.com >>>> --- >>>> include/linux/bpf.h | 14 ++++ >>>> include/uapi/linux/bpf.h | 18 +++++ >>>> kernel/bpf/arraymap.c | 203 ++++++++++++++++++++++++++++++++++++= +++++++++++ >>>> kernel/bpf/verifier.c | 12 ++- >>>> 4 files changed, 246 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >>>> index fa9a988400d9..eae4ce4542c1 100644 >>>> --- a/include/linux/bpf.h >>>> +++ b/include/linux/bpf.h >>>> @@ -13,6 +13,10 @@ >>>> #include >>>> #include >>>> =20 >>>> +#ifdef CONFIG_SECURITY_LANDLOCK >>>> +#include /* struct file */ >>>> +#endif /* CONFIG_SECURITY_LANDLOCK */ >>>> + >>>> struct perf_event; >>>> struct bpf_map; >>>> =20 >>>> @@ -38,6 +42,7 @@ struct bpf_map_ops { >>>> struct bpf_map { >>>> atomic_t refcnt; >>>> enum bpf_map_type map_type; >>>> + enum bpf_map_array_type map_array_type; >>>> u32 key_size; >>>> u32 value_size; >>>> u32 max_entries; >>>> @@ -187,6 +192,9 @@ struct bpf_array { >>>> */ >>>> enum bpf_prog_type owner_prog_type; >>>> bool owner_jited; >>>> +#ifdef CONFIG_SECURITY_LANDLOCK >>>> + u32 n_entries; /* number of entries in a handle array */ >>>> +#endif /* CONFIG_SECURITY_LANDLOCK */ >>>> union { >>>> char value[0] __aligned(8); >>>> void *ptrs[0] __aligned(8); >>>> @@ -194,6 +202,12 @@ struct bpf_array { >>>> }; >>>> }; >>>> =20 >>>> +#ifdef CONFIG_SECURITY_LANDLOCK >>>> +struct map_landlock_handle { >>>> + u32 type; /* enum bpf_map_handle_type */ >>>> +}; >>>> +#endif /* CONFIG_SECURITY_LANDLOCK */ >>>> + >>>> #define MAX_TAIL_CALL_CNT 32 >>>> =20 >>>> struct bpf_event_entry { >>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >>>> index 7cd36166f9b7..b68de57f7ab8 100644 >>>> --- a/include/uapi/linux/bpf.h >>>> +++ b/include/uapi/linux/bpf.h >>>> @@ -87,6 +87,15 @@ enum bpf_map_type { >>>> BPF_MAP_TYPE_PERCPU_ARRAY, >>>> BPF_MAP_TYPE_STACK_TRACE,P_TYPE_CGROUP_ARRAY >>>> BPF_MAP_TYPE_CGROUP_ARRAY, >>>> + BPF_MAP_TYPE_LANDLOCK_ARRAY, >>>> +}; >>>> + >>>> +enum bpf_map_array_type { >>>> + BPF_MAP_ARRAY_TYPE_UNSPEC, >>>> +}; >>>> + >>>> +enum bpf_map_handle_type { >>>> + BPF_MAP_HANDLE_TYPE_UNSPEC, >>>> }; >>> >>> missing something. why it has to be special to have it's own >>> fd array implementation? >>> Please take a look how BPF_MAP_TYPE_PERF_EVENT_ARRAY,=20 >>> BPF_MAP_TYPE_CGROUP_ARRAY and BPF_MAP_TYPE_PROG_ARRAY are done. >>> The all store objects into array map that user space passes via FD. >>> I think the same model should apply here. >> >> The idea is to have multiple way for userland to describe a resource >> (e.g. an open file descriptor, a path or a glob pattern). The kernel >> representation could then be a "struct path *" or dedicated types (e.g= =2E >> custom glob). >=20 > hmm. I think user space api should only deal with FD. Everything > else is user space job to encapsulate/hide. How would you create a FD referring to a glob, a user or port ranges for example ? >=20 >> Another interesting point (that could replace >> check_map_func_compatibility()) is that BPF_MAP_TYPE_LANDLOCK_ARRAY >> translate to dedicated (abstract) types (instead of CONST_PTR_TO_MAP) >> thanks to bpf_reg_type_from_map(). This is useful to abstract userland= >> (map) interface with kernel object(s) dealing with that type. >=20 > I probably missing something. If user space interface is FD, > to the kernel they're different object types. Nothing else. Yes but what if there is more than one way to express a resource (cf. previous comment). A FD can refer to an *existing file* but a glob pattern could match a bunch of files (existing or not). This was a concern for Kees Cook and James Morris [1]. [1] https://lkml.kernel.org/r/CAGXu5jK1U12vMk11HD_x_gNz3Rk4ZgEfdThY7DHvm4e4sP= Rh4g@mail.gmail.com >=20 >> A third point is that BPF_MAP_TYPE_LANDLOCK_ARRAY is a kind of set. It= >> is optimized to quickly walk through all the elements in a sequential = way. >=20 > why set is any faster to walk vs array? 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