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Wed, 16 Oct 2024 15:06:20 -0700 (PDT) MIME-Version: 1.0 References: <20241014215022.68530-1-jeffxu@google.com> <20241014215022.68530-2-jeffxu@google.com> <202410161424.FA6DBA7D91@keescook> In-Reply-To: <202410161424.FA6DBA7D91@keescook> From: Jeff Xu Date: Wed, 16 Oct 2024 15:06:06 -0700 Message-ID: Subject: Re: [RFC PATCH v2 1/1] exec: seal system mappings To: Kees Cook Cc: akpm@linux-foundation.org, jannh@google.com, torvalds@linux-foundation.org, adhemerval.zanella@linaro.org, oleg@redhat.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, jorgelo@chromium.org, sroettger@google.com, ojeda@kernel.org, adobriyan@gmail.com, anna-maria@linutronix.de, mark.rutland@arm.com, linus.walleij@linaro.org, Jason@zx2c4.com, deller@gmx.de, rdunlap@infradead.org, davem@davemloft.net, hch@lst.de, peterx@redhat.com, hca@linux.ibm.com, f.fainelli@gmail.com, gerg@kernel.org, dave.hansen@linux.intel.com, mingo@kernel.org, ardb@kernel.org, Liam.Howlett@oracle.com, mhocko@suse.com, 42.hyeyoo@gmail.com, peterz@infradead.org, ardb@google.com, enh@google.com, rientjes@google.com, groeck@chromium.org, lorenzo.stoakes@oracle.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: yhgc4hjmh51eqi8su5p9z7k3kb1xnecm X-Rspamd-Queue-Id: 52935A0022 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729116373-895593 X-HE-Meta: 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 fL2cXd2T r1VzqrMhBSAWIjKkV1WVoOwn6a8R5I5eUldJR4rQRSh2Fhgi/uWXnNstb1yr8x/c0WZGh/H1xxFjqKVDJfbkTgF58hCFsMbusBCeHzLcg/W1KvnrmogHWgHSigNrMrXngu7Qsj/B9Dy31H9KBM1YyWTG1l5ao8S7w1YHjejc0wLcqjdQ9qXREimKNAVwSc9RPlC1f/PXajjdiRS8GYxdxDHJojdTUD966/2gkT3Rq5cAfOC1VjfGzpW9by1kcBQPHwwTR/kF5ZD5cN7OLp1ewlWEpVH39CRPuG/ExcIdZHxqYBlskNXTILXyNmEccL37a5cOG2dAak7TBEVjeHZ5SCs5aKg== 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 Wed, Oct 16, 2024 at 2:26=E2=80=AFPM Kees Cook wrote: > > (I don't think this needs "RFC" any more) > > On Mon, Oct 14, 2024 at 09:50:20PM +0000, jeffxu@chromium.org wrote: > > From: Jeff Xu > > > > Seal vdso, vvar, sigpage, uprobes and vsyscall. > > > > Those mappings are readonly or executable only, sealing can protect > > them from ever changing during the life time of the process. For > > complete descriptions of memory sealing, please see mseal.rst [1]. > > > > System mappings such as vdso, vvar, and sigpage (for arm) are > > generated by the kernel during program initialization. These mappings > > are designated as non-writable, and sealing them will prevent them > > from ever becoming writeable. > > > > Unlike the aforementioned mappings, the uprobe mapping is not > > established during program startup. However, its lifetime is the same > > as the process's lifetime [2], thus sealable. > > > > The vdso, vvar, sigpage, and uprobe mappings all invoke the > > _install_special_mapping() function. As no other mappings utilize this > > function, it is logical to incorporate sealing logic within > > _install_special_mapping(). This approach avoids the necessity of > > modifying code across various architecture-specific implementations. > > > > The vsyscall mapping, which has its own initialization function, is > > sealed in the XONLY case, it seems to be the most common and secure > > case of using vsyscall. > > > > It is important to note that the CHECKPOINT_RESTORE feature (CRIU) may > > alter the mapping of vdso, vvar, and sigpage during restore > > operations. Consequently, this feature cannot be universally enabled > > across all systems. To address this, a kernel configuration option has > > been introduced to enable or disable this functionality. Note, uprobe > > is always sealed and not controlled by this kernel configuration. > > > > [1] Documentation/userspace-api/mseal.rst > > [2] https://lore.kernel.org/all/CABi2SkU9BRUnqf70-nksuMCQ+yyiWjo3fM4XkR= kL-NrCZxYAyg@mail.gmail.com/ > > > > Signed-off-by: Jeff Xu > > --- > > .../admin-guide/kernel-parameters.txt | 10 ++++ > > arch/x86/entry/vsyscall/vsyscall_64.c | 9 +++- > > fs/exec.c | 53 +++++++++++++++++++ > > include/linux/fs.h | 1 + > > kernel/events/uprobes.c | 2 +- > > mm/mmap.c | 1 + > > security/Kconfig | 26 +++++++++ > > 7 files changed, 99 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Document= ation/admin-guide/kernel-parameters.txt > > index e7bfe1bde49e..02e5eb23d76f 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1538,6 +1538,16 @@ > > Permit 'security.evm' to be updated regardless of > > current integrity status. > > > > + exec.seal_system_mappings =3D [KNL] > > + Format: { never | always } > > + Seal system mappings: vdso, vvar, sigpage, uprobe= s, > > + vsyscall. > > + This overwrites KCONFIG CONFIG_SEAL_SYSTEM_MAPPIN= GS_* > > + - 'never': never seal system mappings. > > + - 'always': always seal system mappings. > > + If not specified or invalid, default is the KCONF= IG value. > > + This option has no effect if CONFIG_64BIT=3Dn > > + > > Any reason for "always"/"never" instead of the more traditional y/n > enabled/disabled, etc? > Yes. I like to leave room for future extension, in case someone ever needs a prctl for pre-process opt-in, e.g. Format:{never|prctl|always} > Otherwise, this all makes sense to me. > > -- > Kees Cook