On Mon, Feb 24, 2025 at 11:03 AM Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> wrote: > > * 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? > Sorry, I pasted the code path from ChromeOS code base, it is actually in the kernel itself. fs/proc/task_mmu.c > > > > #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. > As above, this is actually kernel code, not test. -Jeff > > > > 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
