Re: [PATCH v6 1/7] mseal, system mappings: kernel config and header change

Dave Hansen
2025-02-24T18:21:47Z

On 2/24/25 09:45, jeffxu@chromium.org 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

?

Then all the users could just do:

vm_flags = VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|VM_PFNMAP|
VM_SEALED

That seems to be a the common way of doing things. Take a look at:

# define VM_GROWSUP VM_NONE
...
# define VM_MTE VM_NONE
# define VM_MTE_ALLOWED VM_NONE
...
# define VM_UFFD_MINOR VM_NONE
...
#define VM_DROPPABLE VM_NONE

... and more