On Wed, Oct 16, 2024 at 3:06 PM Jeff Xu <jeffxu@xxxxxxxxxxxx> wrote: > > On Wed, Oct 16, 2024 at 2:26 PM Kees Cook <kees@xxxxxxxxxx> wrote: > > > > (I don't think this needs "RFC" any more) > > > > On Mon, Oct 14, 2024 at 09:50:20PM +0000, jeffxu@xxxxxxxxxxxx wrote: > > > From: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > > > > > 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+yyiWjo3fM4XkRkL-NrCZxYAyg@xxxxxxxxxxxxxx/ > > > > > > Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > > --- > > > .../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/Documentation/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 = [KNL] > > > + Format: { never | always } > > > + Seal system mappings: vdso, vvar, sigpage, uprobes, > > > + vsyscall. > > > + This overwrites KCONFIG CONFIG_SEAL_SYSTEM_MAPPINGS_* > > > + - 'never': never seal system mappings. > > > + - 'always': always seal system mappings. > > > + If not specified or invalid, default is the KCONFIG value. > > > + This option has no effect if CONFIG_64BIT=n > > > + > > > > 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} > I copied the pattern from: proc_mem.force_override= [KNL] Format: {always | ptrace | never} > > Otherwise, this all makes sense to me. > > > > -- > > Kees Cook
