Re: [PATCH v22 21/28] mm: Re-introduce vm_flags to do_mmap()

[Liam Howlett <liam.howlett@oracle.com>]

* Yu-cheng Yu <yu-cheng.yu@intel.com> [210310 17:02]:
> There was no more caller passing vm_flags to do_mmap(), and vm_flags was
> removed from the function's input by:
> 
>     commit 45e55300f114 ("mm: remove unnecessary wrapper function do_mmap_pgoff()").
> 
> There is a new user now.  Shadow stack allocation passes VM_SHSTK to
> do_mmap().  Re-introduce vm_flags to do_mmap(), but without the old wrapper
> do_mmap_pgoff().  Instead, make all callers of the wrapper pass a zero
> vm_flags to do_mmap().

In a later patch, PROT_SHSTK is introduced.  do_mmap() already takes the
PROT flags.  Could PROT_SHSTK be used to indicate VM_SHSTK instead of
expanding the arguments passed to do_mmap()?

> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reviewed-by: Peter Collingbourne <pcc@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: linux-mm@kvack.org
> ---
>  fs/aio.c           |  2 +-
>  include/linux/mm.h |  3 ++-
>  ipc/shm.c          |  2 +-
>  mm/mmap.c          | 10 +++++-----
>  mm/nommu.c         |  4 ++--
>  mm/util.c          |  2 +-
>  6 files changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 1f32da13d39e..b5d0586209a7 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -529,7 +529,7 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
>  
>  	ctx->mmap_base = do_mmap(ctx->aio_ring_file, 0, ctx->mmap_size,
>  				 PROT_READ | PROT_WRITE,
> -				 MAP_SHARED, 0, &unused, NULL);
> +				 MAP_SHARED, 0, 0, &unused, NULL);
>  	mmap_write_unlock(mm);
>  	if (IS_ERR((void *)ctx->mmap_base)) {
>  		ctx->mmap_size = 0;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e363173f7634..2731889f49c1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2543,7 +2543,8 @@ extern unsigned long mmap_region(struct file *file, unsigned long addr,
>  	struct list_head *uf);
>  extern unsigned long do_mmap(struct file *file, unsigned long addr,
>  	unsigned long len, unsigned long prot, unsigned long flags,
> -	unsigned long pgoff, unsigned long *populate, struct list_head *uf);
> +	vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
> +	struct list_head *uf);
>  extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
>  		       struct list_head *uf, bool downgrade);
>  extern int do_munmap(struct mm_struct *, unsigned long, size_t,
> diff --git a/ipc/shm.c b/ipc/shm.c
> index febd88daba8c..b6370eb1eaab 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1556,7 +1556,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
>  			goto invalid;
>  	}
>  
> -	addr = do_mmap(file, addr, size, prot, flags, 0, &populate, NULL);
> +	addr = do_mmap(file, addr, size, prot, flags, 0, 0, &populate, NULL);
>  	*raddr = addr;
>  	err = 0;
>  	if (IS_ERR_VALUE(addr))
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 2ac67882ace2..99077171010b 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1401,11 +1401,11 @@ static inline bool file_mmap_ok(struct file *file, struct inode *inode,
>   */
>  unsigned long do_mmap(struct file *file, unsigned long addr,
>  			unsigned long len, unsigned long prot,
> -			unsigned long flags, unsigned long pgoff,
> -			unsigned long *populate, struct list_head *uf)
> +			unsigned long flags, vm_flags_t vm_flags,
> +			unsigned long pgoff, unsigned long *populate,
> +			struct list_head *uf)
>  {
>  	struct mm_struct *mm = current->mm;
> -	vm_flags_t vm_flags;
>  	int pkey = 0;
>  
>  	*populate = 0;
> @@ -1467,7 +1467,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>  	 * to. we assume access permissions have been handled by the open
>  	 * of the memory object, so we don't do any here.
>  	 */
> -	vm_flags = calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
> +	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
>  			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
>  
>  	if (flags & MAP_LOCKED)
> @@ -3047,7 +3047,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
>  
>  	file = get_file(vma->vm_file);
>  	ret = do_mmap(vma->vm_file, start, size,
> -			prot, flags, pgoff, &populate, NULL);
> +			prot, flags, 0, pgoff, &populate, NULL);
>  	fput(file);
>  out:
>  	mmap_write_unlock(mm);
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 5c9ab799c0e6..9b6f7a1895c2 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1071,6 +1071,7 @@ unsigned long do_mmap(struct file *file,
>  			unsigned long len,
>  			unsigned long prot,
>  			unsigned long flags,
> +			vm_flags_t vm_flags,
>  			unsigned long pgoff,
>  			unsigned long *populate,
>  			struct list_head *uf)
> @@ -1078,7 +1079,6 @@ unsigned long do_mmap(struct file *file,
>  	struct vm_area_struct *vma;
>  	struct vm_region *region;
>  	struct rb_node *rb;
> -	vm_flags_t vm_flags;
>  	unsigned long capabilities, result;
>  	int ret;
>  
> @@ -1097,7 +1097,7 @@ unsigned long do_mmap(struct file *file,
>  
>  	/* we've determined that we can make the mapping, now translate what we
>  	 * now know into VMA flags */
> -	vm_flags = determine_vm_flags(file, prot, flags, capabilities);
> +	vm_flags |= determine_vm_flags(file, prot, flags, capabilities);
>  
>  	/* we're going to need to record the mapping */
>  	region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
> diff --git a/mm/util.c b/mm/util.c
> index 54870226cea6..49cbd4400d13 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -516,7 +516,7 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
>  	if (!ret) {
>  		if (mmap_write_lock_killable(mm))
>  			return -EINTR;
> -		ret = do_mmap(file, addr, len, prot, flag, pgoff, &populate,
> +		ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
>  			      &uf);
>  		mmap_write_unlock(mm);
>  		userfaultfd_unmap_complete(mm, &uf);
> -- 
> 2.21.0
> 
>