* Jeff Xu <jeffxu@xxxxxxxxxxxx> [250224 13:44]: > On Mon, Feb 24, 2025 at 10:21 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > > > On 2/24/25 09:45, jeffxu@xxxxxxxxxxxx wrote: > > > +/* > > > + * mseal of userspace process's system mappings. > > > + */ > > > +#ifdef CONFIG_MSEAL_SYSTEM_MAPPINGS > > > +#define MSEAL_SYSTEM_MAPPINGS_VM_FLAG VM_SEALED > > > +#else > > > +#define MSEAL_SYSTEM_MAPPINGS_VM_FLAG VM_NONE > > > +#endif > > > > This ends up looking pretty wonky in practice: > > > > > + vm_flags = VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|VM_PFNMAP; > > > + vm_flags |= MSEAL_SYSTEM_MAPPINGS_VM_FLAG; > > > > because MSEAL_SYSTEM_MAPPINGS_VM_FLAG is so much different from the > > other ones. > > > > Would it really hurt to have > > > > #ifdef CONFIG_64BIT > > /* VM is sealed, in vm_flags */ > > #define VM_SEALED _BITUL(63) > > +#else > > +#define VM_SEALED VM_NONE > > #endif > > > > ? > > > VM_SEALED isn't defined in 32-bit systems, and mseal.c isn't part of > the build. This is intentional. Any 32-bit code trying to use the > sealing function or the VM_SEALED flag will immediately fail > compilation. This makes it easier to identify incorrect usage. > The reason that two #defines are needed is because you can have mseal enabled while not sealing system mappings, so for this to be clean we need two defines. However MSEAL_SYSTEM_MAPPINGS_VM_FLAG, is _way_ too long, in my opinion. Keeping with "VM_SEALED" I'd suggest "VM_SYSTEM_SEALED". > For example: > Consider the case below in src/third_party/kernel/v6.6/fs/proc/task_mmu.c, third_party? > > #ifdef CONFIG_64BIT > [ilog2(VM_SEALED)] = "sl", > #endif > > Redefining VM_SEALED to VM_NONE for 32 bit won't detect the problem > in case that "#ifdef CONFIG_64BIT" line is missing. I don't think it is reasonable to insist on doing things differently in the kernel because you have external tests that would need updating. These things can change independently, so I don't think this is a valid argument. If these are upstream tests, and we need these tests to work then they can be fixed. > > Please note, this has been like this since the first version of > mseal() RFC patch, and I prefer to keep it this way. Thanks, Liam
