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b=TsxVmgkHn5wz5hbY7X9e3YNY1yGivGCcIOtNeg3iaYGszqvV7YnRbUAHyCeXbbKgz FUdcYygxNjaB9gm3Q41cR98Ivd1A94Q5fiiOwHbgm3cg8DFnYKJkAFjciSp/WTQWSM 8vk1nl3T+71SZ4FTbQLNjV6Z4SvdD7jNc6i1XSGATq4IHdyZI7aWQvZ+SSs4vTBd1R 9NVxrTKMKfsq6lXfhnSv0tMxb/+hWqP5A/Q6ReMb4dNM1opuVkh+Ax2p0li7qNbNWk pG9ABSvmz6ibZwjC+ayCzcinjeWngw046Nxs71xsBefPtZ9CjiPdWBCPFXDorKRZE9 KC3xE1ArkomLg== Date: Thu, 4 Dec 2025 19:40:23 -0800 From: Kees Cook To: Andrei Vagin Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, criu@lists.linux.dev, Tejun Heo , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Vipin Sharma , Jonathan Corbet Subject: Re: [PATCH 1/3] cgroup, binfmt_elf: Add hwcap masks to the misc controller Message-ID: <202512041939.63DA7C96C2@keescook> References: <20251205005841.3942668-1-avagin@google.com> <20251205005841.3942668-2-avagin@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251205005841.3942668-2-avagin@google.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A41C7C000A X-Stat-Signature: kw9cuekkuebq41d1supzjuxwb3n7fz86 X-Rspam-User: X-HE-Tag: 1764906024-676691 X-HE-Meta: U2FsdGVkX19D80/gjxi6rUvb/A+1GCy6zXTqVE2aHdjTh1pkERduVWytQbCOkdnyB1Coj6TrTUAdGCrjRz3XNCEJ4CiQbWMQwZ6oh7pTLcORwLnc943KvhvXzawpRZpBJTUKwM9KoX+t/rEMS4adqh99uCwIuOB8uxjLURvcuVHqNNacks6rA0XIVxjxhmZgwKS2oG8H6+PGPEKPWobOv1dO9jEyao1y8Cbq7nPEC4j9T43NaP//wCYU2uvKPg2uIv6bpTV11K3tozk/wemGu7I0y/rQuSK/cjpUO7+a/9a1kOdqrhH3C9tAlMUggwJA+YcZ5INHQIczaexAS5HP6RdS1ufRpHo5col/e67KcX70GGhkTGT7JUPBjVGTjOD4EKaOGJTNgjIRY5yXshSJUsHbqhaR7FV9urc2ABY6vlcz8TSbTL8DYqKl9XgNv9hOicFwQ4vS6TDbmdcxc8W8i0F/quTjqG5XdGB4vMHAUYRHPPTwE9maor9kj7m8Q3q2l5FS4W1nhPuQMizOJO3G557nlNEtcw4pbNI4dPm7pjGbHTbEhbjg33/ifqJEOYt+uOyFBZzygCzaakHhsCGyQgIxtgWV3S3NlD0MYvYPcMhE3zQYGPNXPfksUUTH4phymCMINnym4pb9afmb55F74lThX/IaqkkcTW0sK/FOjr3nW/QVUiSCkgWKEpULXqw7HHjdwZm0/KIDD9twFD09r6OQN8i9qccQO51UaM3uYdZbd3VhlCZsIyIVeVk+9tmzGdQR36i0rPWdPXa1NB+bMpW2niIhyHnWRKzxSG7S5sQP8YNcKwOiY1eTd24noGa5LsOp3AstZRKYFT1XAid9QR4Hww1pRLKXIPY7QaqR+kq2T4sj2YRdb2y83Gt8wOkeK1Sx28AoHFCoE/DG8+4EDpzbHLcRCRn4U+pMkyIhrvxaZHvFHCk67HtsgVt3UbUuNRK/b5/HuACpUQ3ihbc 025KfBfP i0xVD3TLEmiy9YWtgqUZlrSJ4dWuFXkB9jQyK4jz0JW2rEIveQPtnOCBrhK4Vzx9fH9mKDSwsL0J3M89lRCbvfSQKdczTcOJ8N08NHxcikPKfWW0hxH1KcPJQsZxbaVOJB9AelRQCxguMl1cjFnXOSn25wxv9fP35Ap7zCC17pVrZQxhi8evtM0qTpLsFSe4bDTBNPUvBHkipD2KE8t4PdPUX2o3iJ89tD7lR/jtEyQ5H0JL4vd7Ltom4eor9y9xSucqHbNaXqmfNZpX+7i4gUxQ+VocCTZF/JKpcv7KZwPkCF1hyN1sUEVjf0Hp18JwH+hPupGYskMb1YDAZzNlEW52F3T16r/AZH8H4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Dec 05, 2025 at 12:58:29AM +0000, Andrei Vagin wrote: > Add an interface to the misc cgroup controller that allows masking out > hardware capabilities (AT_HWCAP) reported to user-space processes. This > provides a mechanism to restrict the features a containerized > application can see. > > The new "misc.mask" cgroup file allows users to specify masks for > AT_HWCAP, AT_HWCAP2, AT_HWCAP3, and AT_HWCAP4. > > The output of "misc.mask" is extended to display the effective mask, > which is a combination of the masks from the current cgroup and all its > ancestors. > > Signed-off-by: Andrei Vagin > --- > fs/binfmt_elf.c | 24 +++++-- > include/linux/misc_cgroup.h | 25 +++++++ > kernel/cgroup/misc.c | 126 ++++++++++++++++++++++++++++++++++++ > 3 files changed, 171 insertions(+), 4 deletions(-) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 3eb734c192e9..59137784e81d 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -47,6 +47,7 @@ > #include > #include > #include > +#include > #include > #include > > @@ -182,6 +183,21 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, > int ei_index; > const struct cred *cred = current_cred(); > struct vm_area_struct *vma; > + struct misc_cg *misc_cg; > + u64 hwcap_mask[4] = {0, 0, 0, 0}; > + > + misc_cg = get_current_misc_cg(); > + misc_cg_get_mask(MISC_CG_MASK_HWCAP, misc_cg, &hwcap_mask[0]); > +#ifdef ELF_HWCAP2 > + misc_cg_get_mask(MISC_CG_MASK_HWCAP2, misc_cg, &hwcap_mask[1]); > +#endif > +#ifdef ELF_HWCAP3 > + misc_cg_get_mask(MISC_CG_MASK_HWCAP3, misc_cg, &hwcap_mask[2]); > +#endif > +#ifdef ELF_HWCAP4 > + misc_cg_get_mask(MISC_CG_MASK_HWCAP4, misc_cg, &hwcap_mask[3]); > +#endif Can we avoid having the open-coded 4, 0, 1, 2, 3 where these are used? I imagine it also doesn't need to be a 4 element array if ELF_HWCAP4 isn't defined, etc? -- Kees Cook