Re: [PATCH v9 1/7] mseal sysmap: kernel config and header change

[Lorenzo Stoakes]

On Wed, Mar 05, 2025 at 02:17:05AM +0000, jeffxu@xxxxxxxxxxxx wrote:
> From: Jeff Xu <jeffxu@xxxxxxxxxxxx>
>
> Provide infrastructure to mseal system mappings. Establish
> two kernel configs (CONFIG_MSEAL_SYSTEM_MAPPINGS,
> ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS) and VM_SEALED_SYSMAP
> macro for future patches.
>
> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> Reviewed-by: Kees Cook <kees@xxxxxxxxxx>

Umm... I reviewed this too? :) unless you made substantial changes here
(doesn't appear so), please do propagate tags for each revision :>)

Anyway, FWIW:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

> ---
>  include/linux/mm.h | 10 ++++++++++
>  init/Kconfig       | 22 ++++++++++++++++++++++
>  security/Kconfig   | 21 +++++++++++++++++++++
>  3 files changed, 53 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7b1068ddcbb7..8b800941678d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4155,4 +4155,14 @@ int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *st
>  int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status);
>  int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
>
> +
> +/*
> + * mseal of userspace process's system mappings.
> + */
> +#ifdef CONFIG_MSEAL_SYSTEM_MAPPINGS
> +#define VM_SEALED_SYSMAP	VM_SEALED
> +#else
> +#define VM_SEALED_SYSMAP	VM_NONE
> +#endif
> +
>  #endif /* _LINUX_MM_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index d0d021b3fa3b..7f67d8942a09 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1882,6 +1882,28 @@ config ARCH_HAS_MEMBARRIER_CALLBACKS
>  config ARCH_HAS_MEMBARRIER_SYNC_CORE
>  	bool
>
> +config ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
> +	bool
> +	help
> +	  Control MSEAL_SYSTEM_MAPPINGS access based on architecture.
> +
> +	  A 64-bit kernel is required for the memory sealing feature.
> +	  No specific hardware features from the CPU are needed.
> +
> +	  To enable this feature, the architecture needs to update their
> +	  special mappings calls to include the sealing flag and confirm
> +	  that it doesn't unmap/remap system mappings during the life
> +	  time of the process. The existence of this flag for an architecture
> +	  implies that it does not require the remapping of the system
> +	  mappings during process lifetime, so sealing these mappings is safe
> +	  from a kernel perspective.
> +
> +	  After the architecture enables this, a distribution can set
> +	  CONFIG_MSEAL_SYSTEM_MAPPING to manage access to the feature.
> +
> +	  For complete descriptions of memory sealing, please see
> +	  Documentation/userspace-api/mseal.rst
> +
>  config HAVE_PERF_EVENTS
>  	bool
>  	help
> diff --git a/security/Kconfig b/security/Kconfig
> index f10dbf15c294..a914a02df27e 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -51,6 +51,27 @@ config PROC_MEM_NO_FORCE
>
>  endchoice
>
> +config MSEAL_SYSTEM_MAPPINGS
> +	bool "mseal system mappings"
> +	depends on 64BIT
> +	depends on ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
> +	depends on !CHECKPOINT_RESTORE
> +	help
> +	  Apply mseal on system mappings.
> +	  The system mappings includes vdso, vvar, vvar_vclock,
> +	  vectors (arm compat-mode), sigpage (arm compat-mode), uprobes.
> +
> +	  A 64-bit kernel is required for the memory sealing feature.
> +	  No specific hardware features from the CPU are needed.
> +
> +	  WARNING: This feature breaks programs which rely on relocating
> +	  or unmapping system mappings. Known broken software at the time
> +	  of writing includes CHECKPOINT_RESTORE, UML, gVisor, rr. Therefore
> +	  this config can't be enabled universally.
> +
> +	  For complete descriptions of memory sealing, please see
> +	  Documentation/userspace-api/mseal.rst
> +
>  config SECURITY
>  	bool "Enable different security models"
>  	depends on SYSFS
> --
> 2.48.1.711.g2feabab25a-goog
>