RE: [RFC 07/12] x86/mm: Add helper functions to track encrypted VMA's

["Huang, Kai" <kai.huang@intel.com>]

> -----Original Message-----
> From: keyrings-owner@vger.kernel.org [mailto:keyrings-
> owner@vger.kernel.org] On Behalf Of Alison Schofield
> Sent: Saturday, September 8, 2018 10:37 AM
> To: dhowells@redhat.com; tglx@linutronix.de
> Cc: Huang, Kai <kai.huang@intel.com>; Nakajima, Jun
> <jun.nakajima@intel.com>; Shutemov, Kirill <kirill.shutemov@intel.com>;
> Hansen, Dave <dave.hansen@intel.com>; Sakkinen, Jarkko
> <jarkko.sakkinen@intel.com>; jmorris@namei.org; keyrings@vger.kernel.org;
> linux-security-module@vger.kernel.org; mingo@redhat.com; hpa@zytor.com;
> x86@kernel.org; linux-mm@kvack.org
> Subject: [RFC 07/12] x86/mm: Add helper functions to track encrypted VMA's
> 
> In order to safely manage the usage of memory encryption keys, VMA's using
> each keyid need to be tracked. This tracking allows the Kernel Key Service to
> know when the keyid resource is actually in use, or when it is idle and may be
> considered for reuse.
> 
> Define a global atomic encrypt_count array to track the number of VMA's
> oustanding for each encryption keyid.
> 
> Implement helper functions to manipulate this encrypt_count array.
> 
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> ---
>  arch/x86/include/asm/mktme.h |  7 +++++++
>  arch/x86/mm/mktme.c          | 39
> +++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h           |  2 ++
>  3 files changed, 48 insertions(+)
> 
> diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
> index b707f800b68f..5f3fa0c39c1c 100644
> --- a/arch/x86/include/asm/mktme.h
> +++ b/arch/x86/include/asm/mktme.h
> @@ -16,6 +16,13 @@ extern int mktme_keyid_shift;
>  /* Set the encryption keyid bits in a VMA */  extern void
> mprotect_set_encrypt(struct vm_area_struct *vma, int newkeyid);
> 
> +/* Manage the references to outstanding VMA's per encryption key */
> +extern int vma_alloc_encrypt_array(void); extern void
> +vma_free_encrypt_array(void); extern int vma_read_encrypt_ref(int
> +keyid); extern void vma_get_encrypt_ref(struct vm_area_struct *vma);
> +extern void vma_put_encrypt_ref(struct vm_area_struct *vma);
> +
>  /* Manage mappings between hardware keyids and userspace keys */  extern
> int mktme_map_alloc(void);  extern void mktme_map_free(void); diff --git
> a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c index
> 5ee7f37e9cd0..5690ef51a79a 100644
> --- a/arch/x86/mm/mktme.c
> +++ b/arch/x86/mm/mktme.c
> @@ -163,6 +163,45 @@ int mktme_map_get_free_keyid(void)
>  	return 0;
>  }
> 
> +/*
> + *  Helper functions manage the encrypt_count[] array that tracks the
> + *  VMA's outstanding for each encryption keyid. The gets & puts are
> + *  used in core mm code that allocates and free's VMA's. The alloc,
> + *  free, and read functions are used by the MKTME key service to
> + *  manage key allocation and programming.
> + */
> +atomic_t *encrypt_count;
> +
> +int vma_alloc_encrypt_array(void)
> +{
> +	encrypt_count = kcalloc(mktme_nr_keyids, sizeof(atomic_t),
> GFP_KERNEL);
> +	if (!encrypt_count)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +void vma_free_encrypt_array(void)
> +{
> +	kfree(encrypt_count);
> +}
> +
> +int vma_read_encrypt_ref(int keyid)
> +{
> +	return atomic_read(&encrypt_count[keyid]);
> +}

I think it's better to move above to security/keys/mktme_keys.c w/ appropriate renaming.  

Thanks,
-Kai
> +
> +void vma_get_encrypt_ref(struct vm_area_struct *vma) {
> +	if (vma_keyid(vma))
> +		atomic_inc(&encrypt_count[vma_keyid(vma)]);
> +}
> +
> +void vma_put_encrypt_ref(struct vm_area_struct *vma) {
> +	if (vma_keyid(vma))
> +		atomic_dec(&encrypt_count[vma_keyid(vma)]);
> +}
> +
>  void prep_encrypted_page(struct page *page, int order, int keyid, bool zero)  {
>  	int i;
> diff --git a/include/linux/mm.h b/include/linux/mm.h index
> 0f9422c7841e..b217c699dbab 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2803,6 +2803,8 @@ static inline void setup_nr_node_ids(void) {}  #ifndef
> CONFIG_X86_INTEL_MKTME  static inline void mprotect_set_encrypt(struct
> vm_area_struct *vma,
>  					int newkeyid) {}
> +static inline void vma_get_encrypt_ref(struct vm_area_struct *vma) {}
> +static inline void vma_put_encrypt_ref(struct vm_area_struct *vma) {}
>  #endif /* CONFIG_X86_INTEL_MKTME */
>  #endif /* __KERNEL__ */
>  #endif /* _LINUX_MM_H */
> --
> 2.14.1