On Thu, Jun 19, 2025, Mike Rapoport wrote: > On Thu, Jun 19, 2025 at 02:06:17PM +0200, Christian Brauner wrote: > > On Thu, Jun 19, 2025 at 02:01:22PM +0300, Mike Rapoport wrote: > > > On Thu, Jun 19, 2025 at 12:38:25PM +0200, Christian Brauner wrote: > > > > On Thu, Jun 19, 2025 at 11:13:49AM +0200, Vlastimil Babka wrote: > > > > > On 6/19/25 09:31, Shivank Garg wrote: > > > > > > Export anon_inode_make_secure_inode() to allow KVM guest_memfd to create > > > > > > anonymous inodes with proper security context. This replaces the current > > > > > > pattern of calling alloc_anon_inode() followed by > > > > > > inode_init_security_anon() for creating security context manually. > > > > > > > > > > > > This change also fixes a security regression in secretmem where the > > > > > > S_PRIVATE flag was not cleared after alloc_anon_inode(), causing > > > > > > LSM/SELinux checks to be bypassed for secretmem file descriptors. > > > > > > > > > > > > As guest_memfd currently resides in the KVM module, we need to export this > > > > > > > > > > Could we use the new EXPORT_SYMBOL_GPL_FOR_MODULES() thingy to make this > > > > > explicit for KVM? > > > > > > > > Oh? Enlighten me about that, if you have a second, please. > > > > > > From Documentation/core-api/symbol-namespaces.rst: > > > > > > The macro takes a comma separated list of module names, allowing only those > > > modules to access this symbol. Simple tail-globs are supported. > > > > > > For example:: > > > > > > EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*") > > > > > > will limit usage of this symbol to modules whoes name matches the given > > > patterns. > > > > Is that still mostly advisory and can still be easily circumenvented? Yes and no. For out-of-tree modules, it's mostly advisory. Though I can imagine if someone tries to report a bug because their module is masquerading as e.g. kvm, then they will be told to go away (in far less polite words :-D). For in-tree modules, the restriction is much more enforceable. Renaming a module to circumvent a restricted export will raise major red flags, and getting "proper" access to a symbol would require an ack from the relevant maintainers. E.g. for many KVM-induced exports, it's not that other module writers are trying to misbehave, there simply aren't any guardrails to deter them from using a "dangerous" export. The other big benefit I see is documentation, e.g. both for readers/developers to understand the intent, and for auditing purposes (I would be shocked if there aren't exports that were KVM-induced, but that are no longer necessary). And we can utilize the framework to do additional hardening. E.g. for exports that exist solely for KVM, I plan on adding wrappers so that the symbols are exproted if and only if KVM is enabled in the kernel .config[*]. Again, that's far from perfect, e.g. AFAIK every distro enables KVM, but it should help keep everyone honest. [*] https://lore.kernel.org/all/ZzJOoFFPjrzYzKir@xxxxxxxxxx > The commit message says > > will limit the use of said function to kvm.ko, any other module trying > to use this symbol will refure to load (and get modpost build > failures). To Christian's point, the restrictions are trivial to circumvent by out-of-tree modules. E.g. to get access to the above, simply name your module kvm-lol.ko or whatever.
