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

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Message-ID: <443992d7-f694-4e46-b120-545350a5d598@intel.com>
Date: Mon, 24 Feb 2025 10:21:47 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: jeffxu@...omium.org, akpm@...ux-foundation.org, keescook@...omium.org,
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Subject: Re: [PATCH v6 1/7] mseal, system mappings: kernel config and header
 change

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