linux-kernel - Re: [PATCH v2 2/4] mm, madvise: extract mm code from prctl_set

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Message-ID: <5f5b83ae-8482-4eea-9df0-55871c30375b@redhat.com>
Date: Tue, 24 Jun 2025 16:04:12 +0200
From: David Hildenbrand <david@...hat.com>
To: Vlastimil Babka <vbabka@...e.cz>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Jann Horn <jannh@...gle.com>,
 Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Colin Cross <ccross@...gle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] mm, madvise: extract mm code from prctl_set_vma()
 to mm/madvise.c

On 24.06.25 15:03, Vlastimil Babka wrote:
> Setting anon_name is done via madvise_set_anon_name() and behaves a lot
> of like other madvise operations. However, apparently because madvise()
> has lacked the 4th argument and prctl() not, the userspace entry point
> has been implemented via prctl(PR_SET_VMA, ...) and handled first by
> prctl_set_vma().
> 
> Currently prctl_set_vma() lives in kernel/sys.c but setting the
> vma->anon_name is mm-specific code so extract it to a new
> set_anon_vma_name() function under mm. mm/madvise.c seems to be the most
> straightforward place as that's where madvise_set_anon_name() lives.
> Stop declaring the latter in mm.h and instead declare
> set_anon_vma_name().
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>   include/linux/mm.h | 14 +++++++-------
>   kernel/sys.c       | 50 +-------------------------------------------------
>   mm/madvise.c       | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>   3 files changed, 58 insertions(+), 58 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0e0549f3d681f6c7a78e8dfa341a810e5a8f96c1..ef40f68c1183d4c95016575a4ee0171e12df9ba4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4059,14 +4059,14 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
>   #endif
>   
>   #ifdef CONFIG_ANON_VMA_NAME
> -int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> -			  unsigned long len_in,
> -			  struct anon_vma_name *anon_name);
> +int set_anon_vma_name(unsigned long addr, unsigned long size,
> +		      const char __user *uname);
>   #else
> -static inline int
> -madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> -		      unsigned long len_in, struct anon_vma_name *anon_name) {
> -	return 0;
> +static inline
> +int set_anon_vma_name(unsigned long addr, unsigned long size,
> +		      const char __user *uname)
> +{
> +	return -EINVAL;
>   }
>   #endif
>   
> diff --git a/kernel/sys.c b/kernel/sys.c
> index adc0de0aa364aebb23999f621717a5d32599921c..b153fb345ada28ea1a33386a32bcce9cb1b23475 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2343,54 +2343,14 @@ int __weak arch_lock_shadow_stack_status(struct task_struct *t, unsigned long st
>   
>   #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
>   
> -#ifdef CONFIG_ANON_VMA_NAME
> -
> -#define ANON_VMA_NAME_MAX_LEN		80
> -#define ANON_VMA_NAME_INVALID_CHARS	"\\`$[]"
> -
> -static inline bool is_valid_name_char(char ch)
> -{
> -	/* printable ascii characters, excluding ANON_VMA_NAME_INVALID_CHARS */
> -	return ch > 0x1f && ch < 0x7f &&
> -		!strchr(ANON_VMA_NAME_INVALID_CHARS, ch);
> -}
> -
>   static int prctl_set_vma(unsigned long opt, unsigned long addr,
>   			 unsigned long size, unsigned long arg)
>   {
> -	struct mm_struct *mm = current->mm;
> -	const char __user *uname;
> -	struct anon_vma_name *anon_name = NULL;
>   	int error;
>   
>   	switch (opt) {
>   	case PR_SET_VMA_ANON_NAME:
> -		uname = (const char __user *)arg;
> -		if (uname) {
> -			char *name, *pch;
> -
> -			name = strndup_user(uname, ANON_VMA_NAME_MAX_LEN);
> -			if (IS_ERR(name))
> -				return PTR_ERR(name);
> -
> -			for (pch = name; *pch != '\0'; pch++) {
> -				if (!is_valid_name_char(*pch)) {
> -					kfree(name);
> -					return -EINVAL;
> -				}
> -			}
> -			/* anon_vma has its own copy */
> -			anon_name = anon_vma_name_alloc(name);
> -			kfree(name);
> -			if (!anon_name)
> -				return -ENOMEM;
> -
> -		}
> -
> -		mmap_write_lock(mm);
> -		error = madvise_set_anon_name(mm, addr, size, anon_name);
> -		mmap_write_unlock(mm);
> -		anon_vma_name_put(anon_name);
> +		error = set_anon_vma_name(addr, size, (const char __user *)arg);

At first I thought whether passing current->mm as an argument might make 
it clearer on what we actually operate. But then, "anon_vma" might give 
a good hint.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb