From: Kees Cook <keescook@chromium.org> To: Matthias Kaehlcke <mka@chromium.org> Cc: Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@kernel.org>, James Morris <jmorris@namei.org>, "Serge E . Hallyn" <serge@hallyn.com>, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, Song Liu <song@kernel.org>, linux-security-module@vger.kernel.org, Douglas Anderson <dianders@chromium.org>, dm-devel@redhat.com Subject: Re: [PATCH 0/3] LoadPin: Enable loading from trusted dm-verity devices Date: Mon, 18 Apr 2022 19:33:55 -0700 [thread overview] Message-ID: <202204181931.A618DFF2C@keescook> (raw) In-Reply-To: <Yl3pj72hM/Bo+Kf5@google.com> On Mon, Apr 18, 2022 at 03:43:27PM -0700, Matthias Kaehlcke wrote: > Hi Kees, > > On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote: > > [oops, resending to actual CC list] > > > > On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote: > > > This series extends LoadPin to allow loading of kernel files > > > from trusted dm-verity devices. It adds the concept of > > > trusted verity devices to LoadPin. Userspace can use the > > > new systl file 'loadpin/trusted_verity_root_digests' to > > > provide LoadPin with a list of root digests from dm-verity > > > devices that LoadPin should consider as trusted. When a > > > kernel file is read LoadPin first checks (as usual) whether > > > the file is located on the pinned root, if so the file can > > > be loaded. Otherwise, if the verity extension is enabled, > > > LoadPin determines whether the file is located on a verity > > > backed device and whether the root digest of that device > > > is in the list of trusted digests. The file can be loaded > > > if the verity device has a trusted root digest. > > > > > > The list of trusted root digests can only be written once > > > (typically at boot time), to limit the possiblity of > > > attackers setting up rogue verity devices and marking them > > > as trusted. > > > > Thanks for working all this out! Where does the list of trusted > > roothashes come from? I assume some chain of trust exists. Is the list > > maybe already stored on the rootfs? > > Yes, at least the content of the list comes from the rootfs. The > userspace part is still TBD (also pending on the evolution of this > patchset), having the list pre-formatted in a single file on the > rootfs should be fine. Ah-ha, that's perfect. > > It'd be nice if there was some way to pass the trust chain to LoadPin > > more directly. > > I imagine you envision LoadPin reading the file itself, instead of > just processing the content. That should be doable. One option would > be to pass the path of the file with the hashes through the sysctl > file and use kernel_read_file_from_path() to read it if the path is > in the pinned root (or maybe even in any trusted file system ;-) It could be a boot param or a Kconfig too. But yeah, having LoadPin able to use itself to validate the file path would be much nicer. -- Kees Cook
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org> To: Matthias Kaehlcke <mka@chromium.org> Cc: Douglas Anderson <dianders@chromium.org>, dm-devel@redhat.com, Mike Snitzer <snitzer@kernel.org>, linux-kernel@vger.kernel.org, James Morris <jmorris@namei.org>, linux-raid@vger.kernel.org, Song Liu <song@kernel.org>, linux-security-module@vger.kernel.org, Alasdair Kergon <agk@redhat.com>, "Serge E . Hallyn" <serge@hallyn.com> Subject: Re: [dm-devel] [PATCH 0/3] LoadPin: Enable loading from trusted dm-verity devices Date: Mon, 18 Apr 2022 19:33:55 -0700 [thread overview] Message-ID: <202204181931.A618DFF2C@keescook> (raw) In-Reply-To: <Yl3pj72hM/Bo+Kf5@google.com> On Mon, Apr 18, 2022 at 03:43:27PM -0700, Matthias Kaehlcke wrote: > Hi Kees, > > On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote: > > [oops, resending to actual CC list] > > > > On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote: > > > This series extends LoadPin to allow loading of kernel files > > > from trusted dm-verity devices. It adds the concept of > > > trusted verity devices to LoadPin. Userspace can use the > > > new systl file 'loadpin/trusted_verity_root_digests' to > > > provide LoadPin with a list of root digests from dm-verity > > > devices that LoadPin should consider as trusted. When a > > > kernel file is read LoadPin first checks (as usual) whether > > > the file is located on the pinned root, if so the file can > > > be loaded. Otherwise, if the verity extension is enabled, > > > LoadPin determines whether the file is located on a verity > > > backed device and whether the root digest of that device > > > is in the list of trusted digests. The file can be loaded > > > if the verity device has a trusted root digest. > > > > > > The list of trusted root digests can only be written once > > > (typically at boot time), to limit the possiblity of > > > attackers setting up rogue verity devices and marking them > > > as trusted. > > > > Thanks for working all this out! Where does the list of trusted > > roothashes come from? I assume some chain of trust exists. Is the list > > maybe already stored on the rootfs? > > Yes, at least the content of the list comes from the rootfs. The > userspace part is still TBD (also pending on the evolution of this > patchset), having the list pre-formatted in a single file on the > rootfs should be fine. Ah-ha, that's perfect. > > It'd be nice if there was some way to pass the trust chain to LoadPin > > more directly. > > I imagine you envision LoadPin reading the file itself, instead of > just processing the content. That should be doable. One option would > be to pass the path of the file with the hashes through the sysctl > file and use kernel_read_file_from_path() to read it if the path is > in the pinned root (or maybe even in any trusted file system ;-) It could be a boot param or a Kconfig too. But yeah, having LoadPin able to use itself to validate the file path would be much nicer. -- Kees Cook -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
next prev parent reply other threads:[~2022-04-19 2:34 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-18 21:15 [PATCH 0/3] LoadPin: Enable loading from trusted dm-verity devices Matthias Kaehlcke 2022-04-18 21:15 ` [dm-devel] " Matthias Kaehlcke 2022-04-18 21:15 ` [PATCH 1/3] dm: Add verity helpers for LoadPin Matthias Kaehlcke 2022-04-18 21:15 ` [dm-devel] " Matthias Kaehlcke 2022-04-18 21:15 ` [PATCH 2/3] LoadPin: Enable loading from trusted dm-verity devices Matthias Kaehlcke 2022-04-18 21:15 ` [dm-devel] " Matthias Kaehlcke 2022-04-19 4:32 ` kernel test robot 2022-04-19 4:32 ` [dm-devel] " kernel test robot 2022-04-18 21:15 ` [PATCH 3/3] dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional compilation Matthias Kaehlcke 2022-04-18 21:15 ` [dm-devel] " Matthias Kaehlcke 2022-04-18 22:14 ` [PATCH 0/3] LoadPin: Enable loading from trusted dm-verity devices Kees Cook 2022-04-18 22:14 ` [dm-devel] " Kees Cook 2022-04-18 22:43 ` Matthias Kaehlcke 2022-04-18 22:43 ` [dm-devel] " Matthias Kaehlcke 2022-04-19 2:33 ` Kees Cook [this message] 2022-04-19 2:33 ` Kees Cook
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