[PATCH v19 6/8] PM: hibernate: disable when there are active secretmem users

[Mark Rutland]

On Thu, May 13, 2021 at 09:47:32PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt at linux.ibm.com>
> 
> It is unsafe to allow saving of secretmem areas to the hibernation
> snapshot as they would be visible after the resume and this essentially
> will defeat the purpose of secret memory mappings.
> 
> Prevent hibernation whenever there are active secret memory users.

Have we thought about how this is going to work in practice, e.g. on
mobile systems? It seems to me that there are a variety of common
applications which might want to use this which people don't expect to
inhibit hibernate (e.g. authentication agents, web browsers).

Are we happy to say that any userspace application can incidentally
inhibit hibernate?

Thanks,
Mark.

> Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>
> Cc: Alexander Viro <viro at zeniv.linux.org.uk>
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Borislav Petkov <bp at alien8.de>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Christopher Lameter <cl at linux.com>
> Cc: Dan Williams <dan.j.williams at intel.com>
> Cc: Dave Hansen <dave.hansen at linux.intel.com>
> Cc: David Hildenbrand <david at redhat.com>
> Cc: Elena Reshetova <elena.reshetova at intel.com>
> Cc: Hagen Paul Pfeifer <hagen at jauu.net>
> Cc: "H. Peter Anvin" <hpa at zytor.com>
> Cc: Ingo Molnar <mingo at redhat.com>
> Cc: James Bottomley <jejb at linux.ibm.com>
> Cc: "Kirill A. Shutemov" <kirill at shutemov.name>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Matthew Wilcox <willy at infradead.org>
> Cc: Michael Kerrisk <mtk.manpages at gmail.com>
> Cc: Palmer Dabbelt <palmer at dabbelt.com>
> Cc: Palmer Dabbelt <palmerdabbelt at google.com>
> Cc: Paul Walmsley <paul.walmsley at sifive.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Rick Edgecombe <rick.p.edgecombe at intel.com>
> Cc: Roman Gushchin <guro at fb.com>
> Cc: Shakeel Butt <shakeelb at google.com>
> Cc: Shuah Khan <shuah at kernel.org>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Tycho Andersen <tycho at tycho.ws>
> Cc: Will Deacon <will at kernel.org>
> ---
>  include/linux/secretmem.h |  6 ++++++
>  kernel/power/hibernate.c  |  5 ++++-
>  mm/secretmem.c            | 15 +++++++++++++++
>  3 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h
> index e617b4afcc62..21c3771e6a56 100644
> --- a/include/linux/secretmem.h
> +++ b/include/linux/secretmem.h
> @@ -30,6 +30,7 @@ static inline bool page_is_secretmem(struct page *page)
>  }
>  
>  bool vma_is_secretmem(struct vm_area_struct *vma);
> +bool secretmem_active(void);
>  
>  #else
>  
> @@ -43,6 +44,11 @@ static inline bool page_is_secretmem(struct page *page)
>  	return false;
>  }
>  
> +static inline bool secretmem_active(void)
> +{
> +	return false;
> +}
> +
>  #endif /* CONFIG_SECRETMEM */
>  
>  #endif /* _LINUX_SECRETMEM_H */
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index da0b41914177..559acef3fddb 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -31,6 +31,7 @@
>  #include <linux/genhd.h>
>  #include <linux/ktime.h>
>  #include <linux/security.h>
> +#include <linux/secretmem.h>
>  #include <trace/events/power.h>
>  
>  #include "power.h"
> @@ -81,7 +82,9 @@ void hibernate_release(void)
>  
>  bool hibernation_available(void)
>  {
> -	return nohibernate == 0 && !security_locked_down(LOCKDOWN_HIBERNATION);
> +	return nohibernate == 0 &&
> +		!security_locked_down(LOCKDOWN_HIBERNATION) &&
> +		!secretmem_active();
>  }
>  
>  /**
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index 1ae50089adf1..7c2499e4de22 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -40,6 +40,13 @@ module_param_named(enable, secretmem_enable, bool, 0400);
>  MODULE_PARM_DESC(secretmem_enable,
>  		 "Enable secretmem and memfd_secret(2) system call");
>  
> +static atomic_t secretmem_users;
> +
> +bool secretmem_active(void)
> +{
> +	return !!atomic_read(&secretmem_users);
> +}
> +
>  static vm_fault_t secretmem_fault(struct vm_fault *vmf)
>  {
>  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> @@ -94,6 +101,12 @@ static const struct vm_operations_struct secretmem_vm_ops = {
>  	.fault = secretmem_fault,
>  };
>  
> +static int secretmem_release(struct inode *inode, struct file *file)
> +{
> +	atomic_dec(&secretmem_users);
> +	return 0;
> +}
> +
>  static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
>  {
>  	unsigned long len = vma->vm_end - vma->vm_start;
> @@ -116,6 +129,7 @@ bool vma_is_secretmem(struct vm_area_struct *vma)
>  }
>  
>  static const struct file_operations secretmem_fops = {
> +	.release	= secretmem_release,
>  	.mmap		= secretmem_mmap,
>  };
>  
> @@ -202,6 +216,7 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
>  	file->f_flags |= O_LARGEFILE;
>  
>  	fd_install(fd, file);
> +	atomic_inc(&secretmem_users);
>  	return fd;
>  
>  err_put_fd:
> -- 
> 2.28.0
>