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Thu, 20 Feb 2020 23:49:09 +0000 Received: by smtp420.mail.bf1.yahoo.com (Oath Hermes SMTP Server) with ESMTPA ID ce0b481e3b364af6d6326aa7d95a5f82; Thu, 20 Feb 2020 23:49:05 +0000 (UTC) Subject: Re: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs To: KP Singh , LKML , Linux Security Module list References: <20200220175250.10795-1-kpsingh@chromium.org> <20200220175250.10795-4-kpsingh@chromium.org> From: Casey Schaufler Autocrypt: addr=casey@schaufler-ca.com; keydata= mQINBFzV9HABEAC/mmv3jeJyF7lR7QhILYg1+PeBLIMZv7KCzBSc/4ZZipoWdmr77Lel/RxQ 1PrNx0UaM5r6Hj9lJmJ9eg4s/TUBSP67mTx+tsZ1RhG78/WFf9aBe8MSXxY5cu7IUwo0J/CG vdSqACKyYPV5eoTJmnMxalu8/oVUHyPnKF3eMGgE0mKOFBUMsb2pLS/enE4QyxhcZ26jeeS6 3BaqDl1aTXGowM5BHyn7s9LEU38x/y2ffdqBjd3au2YOlvZ+XUkzoclSVfSR29bomZVVyhMB h1jTmX4Ac9QjpwsxihT8KNGvOM5CeCjQyWcW/g8LfWTzOVF9lzbx6IfEZDDoDem4+ZiPsAXC SWKBKil3npdbgb8MARPes2DpuhVm8yfkJEQQmuLYv8GPiJbwHQVLZGQAPBZSAc7IidD2zbf9 XAw1/SJGe1poxOMfuSBsfKxv9ba2i8hUR+PH7gWwkMQaQ97B1yXYxVEkpG8Y4MfE5Vd3bjJU kvQ/tOBUCw5zwyIRC9+7zr1zYi/3hk+OG8OryZ5kpILBNCo+aePeAJ44znrySarUqS69tuXd a3lMPHUJJpUpIwSKQ5UuYYkWlWwENEWSefpakFAIwY4YIBkzoJ/t+XJHE1HTaJnRk6SWpeDf CreF3+LouP4njyeLEjVIMzaEpwROsw++BX5i5vTXJB+4UApTAQARAQABtChDYXNleSBTY2hh dWZsZXIgPGNhc2V5QHNjaGF1Zmxlci1jYS5jb20+iQJUBBMBCAA+FiEEC+9tH1YyUwIQzUIe OKUVfIxDyBEFAlzV9HACGwMFCRLMAwAFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AACgkQOKUV fIxDyBG6ag/6AiRl8yof47YOEVHlrmewbpnlBTaYNfJ5cZflNRKRX6t4bp1B2YV1whlDTpiL vNOwFkh+ZE0eI5M4x8Gw2Oiok+4Q5liA9PHTozQYF+Ia+qdL5EehfbLGoEBqklpGvG3h8JsO 7SvONJuFDgvab/U/UriDYycJwzwKZuhVtK9EMpnTtUDyP3DY+Q8h7MWsniNBLVXnh4yBIEJg SSgDn3COpZoFTPGKE+rIzioo/GJe8CTa2g+ZggJiY/myWTS3quG0FMvwvNYvZ4I2g6uxSl7n bZVqAZgqwoTAv1HSXIAn9muwZUJL03qo25PFi2gQmX15BgJKQcV5RL0GHFHRThDS3IyadOgK P2j78P8SddTN73EmsG5OoyzwZAxXfck9A512BfVESqapHurRu2qvMoUkQaW/2yCeRQwGTsFj /rr0lnOBkyC6wCmPSKXe3dT2mnD5KnCkjn7KxLqexKt4itGjJz4/ynD/qh+gL7IPbifrQtVH JI7cr0fI6Tl8V6efurk5RjtELsAlSR6fKV7hClfeDEgLpigHXGyVOsynXLr59uE+g/+InVic jKueTq7LzFd0BiduXGO5HbGyRKw4MG5DNQvC//85EWmFUnDlD3WHz7Hicg95D+2IjD2ZVXJy x3LTfKWdC8bU8am1fi+d6tVEFAe/KbUfe+stXkgmfB7pxqW5Ag0EXNX0cAEQAPIEYtPebJzT wHpKLu1/j4jQcke06Kmu5RNuj1pEje7kX5IKzQSs+CPH0NbSNGvrA4dNGcuDUTNHgb5Be9hF zVqRCEvF2j7BFbrGe9jqMBWHuWheQM8RRoa2UMwQ704mRvKr4sNPh01nKT52ASbWpBPYG3/t WbYaqfgtRmCxBnqdOx5mBJIBh9Q38i63DjQgdNcsTx2qS7HFuFyNef5LCf3jogcbmZGxG/b7 yF4OwmGsVc8ufvlKo5A9Wm+tnRjLr/9Mn9vl5Xa/tQDoPxz26+aWz7j1in7UFzAarcvqzsdM Em6S7uT+qy5jcqyuipuenDKYF/yNOVSNnsiFyQTFqCPCpFihOnuaWqfmdeUOQHCSo8fD4aRF emsuxqcsq0Jp2ODq73DOTsdFxX2ESXYoFt3Oy7QmIxeEgiHBzdKU2bruIB5OVaZ4zWF+jusM Uh+jh+44w9DZkDNjxRAA5CxPlmBIn1OOYt1tsphrHg1cH1fDLK/pDjsJZkiH8EIjhckOtGSb aoUUMMJ85nVhN1EbU/A3DkWCVFEA//Vu1+BckbSbJKE7Hl6WdW19BXOZ7v3jo1q6lWwcFYth esJfk3ZPPJXuBokrFH8kqnEQ9W2QgrjDX3et2WwZFLOoOCItWxT0/1QO4ikcef/E7HXQf/ij Dxf9HG2o5hOlMIAkJq/uLNMvABEBAAGJAjwEGAEIACYWIQQL720fVjJTAhDNQh44pRV8jEPI EQUCXNX0cAIbDAUJEswDAAAKCRA4pRV8jEPIEWkzEACKFUnpp+wIVHpckMfBqN8BE5dUbWJc GyQ7wXWajLtlPdw1nNw0Wrv+ob2RCT7qQlUo6GRLcvj9Fn5tR4hBvR6D3m8aR0AGHbcC62cq I7LjaSDP5j/em4oVL2SMgNTrXgE2w33JMGjAx9oBzkxmKUqprhJomPwmfDHMJ0t7y39Da724 oLPTkQDpJL1kuraM9TC5NyLe1+MyIxqM/8NujoJbWeQUgGjn9uxQAil7o/xSCjrWCP3kZDID vd5ZaHpdl8e1mTExQoKr4EWgaMjmD/a3hZ/j3KfTVNpM2cLfD/QwTMaC2fkK8ExMsz+rUl1H icmcmpptCwOSgwSpPY1Zfio6HvEJp7gmDwMgozMfwQuT9oxyFTxn1X3rn1IoYQF3P8gsziY5 qtTxy2RrgqQFm/hr8gM78RhP54UPltIE96VywviFzDZehMvuwzW//fxysIoK97Y/KBZZOQs+ /T+Bw80Pwk/dqQ8UmIt2ffHEgwCTbkSm711BejapWCfklxkMZDp16mkxSt2qZovboVjXnfuq wQ1QL4o4t1hviM7LyoflsCLnQFJh6RSBhBpKQinMJl/z0A6NYDkQi6vEGMDBWX/M2vk9Jvwa v0cEBfY3Z5oFgkh7BUORsu1V+Hn0fR/Lqq/Pyq+nTR26WzGDkolLsDr3IH0TiAVH5ZuPxyz6 abzjfg== Message-ID: <0ef26943-9619-3736-4452-fec536a8d169@schaufler-ca.com> Date: Thu, 20 Feb 2020 15:49:05 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200220175250.10795-4-kpsingh@chromium.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-Mailer: WebService/1.1.15199 hermes Apache-HttpAsyncClient/4.1.4 (Java/1.8.0_241) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/20/2020 9:52 AM, KP Singh wrote: > From: KP Singh Sorry about the heavy list pruning - the original set blows thunderbird up. > > The BPF LSM programs are implemented as fexit trampolines to avoid the > overhead of retpolines. These programs cannot be attached to security_*= > wrappers as there are quite a few security_* functions that do more tha= n > just calling the LSM callbacks. > > This was discussed on the lists in: > > https://lore.kernel.org/bpf/20200123152440.28956-1-kpsingh@chromium.o= rg/T/#m068becce588a0cdf01913f368a97aea4c62d8266 > > Adding a NOP callback after all the static LSM callbacks are called has= > the following benefits: > > - The BPF programs run at the right stage of the security_* wrappers. > - They run after all the static LSM hooks allowed the operation, > therefore cannot allow an action that was already denied. I still say that the special call-out to BPF is unnecessary. I remain unconvinced by the arguments. You aren't doing anything so special that the general mechanism won't work. > > There are some hooks which do not call call_int_hooks or > call_void_hooks. It's not possible to call the bpf_lsm_* functions > without checking if there is BPF LSM program attached to these hooks. > This is added further in a subsequent patch. For now, these hooks are > marked as NO_BPF (i.e. attachment of BPF programs is not possible). > > Signed-off-by: KP Singh > --- > include/linux/bpf_lsm.h | 34 ++++++++++++++++++++++++++++++++++ > kernel/bpf/bpf_lsm.c | 16 ++++++++++++++++ > security/security.c | 3 +++ > 3 files changed, 53 insertions(+) > create mode 100644 include/linux/bpf_lsm.h > > diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h > new file mode 100644 > index 000000000000..f867f72f6aa9 > --- /dev/null > +++ b/include/linux/bpf_lsm.h > @@ -0,0 +1,34 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +/* > + * Copyright 2019 Google LLC. > + */ > + > +#ifndef _LINUX_BPF_LSM_H > +#define _LINUX_BPF_LSM_H > + > +#include > + > +#ifdef CONFIG_BPF_LSM > + > +#define LSM_HOOK(RET, NAME, ...) RET bpf_lsm_##NAME(__VA_ARGS__); > +#include > +#undef LSM_HOOK > + > +#define RUN_BPF_LSM_VOID_PROGS(FUNC, ...) bpf_lsm_##FUNC(__VA_ARGS__) > +#define RUN_BPF_LSM_INT_PROGS(RC, FUNC, ...) ({ \ > + do { \ > + if (RC =3D=3D 0) \ > + RC =3D bpf_lsm_##FUNC(__VA_ARGS__); \ > + } while (0); \ > + RC; \ > +}) > + > +#else /* !CONFIG_BPF_LSM */ > + > +#define RUN_BPF_LSM_INT_PROGS(RC, FUNC, ...) (RC) > +#define RUN_BPF_LSM_VOID_PROGS(FUNC, ...) > + > +#endif /* CONFIG_BPF_LSM */ > + > +#endif /* _LINUX_BPF_LSM_H */ > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c > index affb6941622e..abc847c9b9a1 100644 > --- a/kernel/bpf/bpf_lsm.c > +++ b/kernel/bpf/bpf_lsm.c > @@ -7,6 +7,22 @@ > #include > #include > #include > +#include > + > +/* For every LSM hook that allows attachment of BPF programs, declare= a NOP > + * function where a BPF program can be attached as an fexit trampoline= =2E > + */ > +#define LSM_HOOK(RET, NAME, ...) LSM_HOOK_##RET(NAME, __VA_ARGS__) > +#define LSM_HOOK_int(NAME, ...) noinline int bpf_lsm_##NAME(__VA_ARGS_= _) \ > +{ \ > + return 0; \ > +} > + > +#define LSM_HOOK_void(NAME, ...) \ > + noinline void bpf_lsm_##NAME(__VA_ARGS__) {} > + > +#include > +#undef LSM_HOOK > =20 > const struct bpf_prog_ops lsm_prog_ops =3D { > }; > diff --git a/security/security.c b/security/security.c > index 565bc9b67276..aa111392a700 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > =20 > #define MAX_LSM_EVM_XATTR 2 > =20 > @@ -684,6 +685,7 @@ static void __init lsm_early_task(struct task_struc= t *task) > \ > hlist_for_each_entry(P, &security_hook_heads.FUNC, list) \ > P->hook.FUNC(__VA_ARGS__); \ > + RUN_BPF_LSM_VOID_PROGS(FUNC, __VA_ARGS__); \ > } while (0) > =20 > #define call_int_hook(FUNC, IRC, ...) ({ \ > @@ -696,6 +698,7 @@ static void __init lsm_early_task(struct task_struc= t *task) > if (RC !=3D 0) \ > break; \ > } \ > + RC =3D RUN_BPF_LSM_INT_PROGS(RC, FUNC, __VA_ARGS__); \ > } while (0); \ > RC; \ > })