linux-kernel - Re: [PATCH v8 2/3] mm: add a field to store names for private anonymous memory

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Date:   Wed, 1 Sep 2021 10:09:20 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, ccross@...gle.com,
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Subject: Re: [PATCH v8 2/3] mm: add a field to store names for private
 anonymous memory

On Fri 27-08-21 12:18:57, Suren Baghdasaryan wrote:
[...]
> Userspace can set the name for a region of memory by calling
> prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
> Setting the name to NULL clears it.

Maybe I am missing this part but I do not see this being handled
anywhere.

[...]
> @@ -3283,5 +3283,16 @@ static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_ADVISE_SYSCALLS
> +int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> +			  unsigned long len_in, const char *name);
> +#else
> +static inline int
> +madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> +		      unsigned long len_in, const char *name) {
> +	return 0;
> +}
> +#endif

You want to make this depend on CONFIG_PROC_FS.

[...]
> +#ifdef CONFIG_MMU
> +
> +#define ANON_VMA_NAME_MAX_LEN	64
> +
> +static int prctl_set_vma(unsigned long opt, unsigned long addr,
> +			 unsigned long size, unsigned long arg)
> +{
> +	struct mm_struct *mm = current->mm;
> +	char *name, *pch;
> +	int error;
> +
> +	switch (opt) {
> +	case PR_SET_VMA_ANON_NAME:
> +		name = strndup_user((const char __user *)arg,
> +				    ANON_VMA_NAME_MAX_LEN);
> +
> +		if (IS_ERR(name))
> +			return PTR_ERR(name);

unless I am missing something NULL name would lead to an error rather
than a name clearing as advertised above.

> +
> +		for (pch = name; *pch != '\0'; pch++) {
> +			if (!isprint(*pch)) {
> +				kfree(name);
> +				return -EINVAL;
> +			}
> +		}
> +
> +		mmap_write_lock(mm);
> +		error = madvise_set_anon_name(mm, addr, size, name);
> +		mmap_write_unlock(mm);
> +		kfree(name);
> +		break;
> +	default:
> +		error = -EINVAL;
> +	}
> +
> +	return error;
-- 
Michal Hocko
SUSE Labs