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mm: Add copy_remote_mm_str()

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copy_remote_vm_str() gets the target address space from a struct
task_struct. This does not work for an address space that exists but is
not yet associated with a task_struct, such as the mm held by struct
linux_binprm during exec.

Add copy_remote_mm_str(), which operates directly on a struct mm_struct.

Use a common internal interface for the MMU and NOMMU implementations
and define both public wrappers in mm/util.c. Preserve the existing
copy_remote_vm_str() behavior, including handling zero-length requests
before acquiring the task's mm.

Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Link: https://patch.msgid.link/20260918131757.42802-2-tasos.papagiannnis@gmail.com
This commit is contained in:
Anastasios Papagiannis 2026-09-18 16:17:53 +03:00 committed by Alexei Starovoitov
parent 961b8946ac
commit 69d38c792c
No known key found for this signature in database
5 changed files with 71 additions and 86 deletions
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8
include/linux/mm.h
View File

@ -3325,10 +3325,10 @@ extern int access_process_vm(struct task_struct *tsk, unsigned long addr,
extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
#ifdef CONFIG_BPF_SYSCALL
extern int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
#endif
int copy_remote_mm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
long get_user_pages_remote(struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,

3
mm/internal.h
View File

@ -25,6 +25,9 @@
struct folio_batch;
struct hstate;
int __copy_remote_mm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
struct huge_bootmem_page {
struct list_head list;
struct hstate *hstate;

43
mm/memory.c
View File

@ -7326,13 +7326,12 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr,
}
EXPORT_SYMBOL_GPL(access_process_vm);
#ifdef CONFIG_BPF_SYSCALL
/*
* Copy a string from another process's address space as given in mm.
* If there is any error return -EFAULT.
*/
static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
int __copy_remote_mm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
void *old_buf = buf;
int err = 0;
@ -7408,44 +7407,6 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
return buf - old_buf;
}
/**
* copy_remote_vm_str - copy a string from another process's address space.
* @tsk: the task of the target address space
* @addr: start address to read from
* @buf: destination buffer
* @len: number of bytes to copy
* @gup_flags: flags modifying lookup behaviour
*
* The caller must hold a reference on @mm.
*
* Return: number of bytes copied from @addr (source) to @buf (destination);
* not including the trailing NUL. Always guaranteed to leave NUL-terminated
* buffer. On any error, return -EFAULT.
*/
int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
struct mm_struct *mm;
int ret;
if (unlikely(len == 0))
return 0;
mm = get_task_mm(tsk);
if (!mm) {
*(char *)buf = '\0';
return -EFAULT;
}
ret = __copy_remote_vm_str(mm, addr, buf, len, gup_flags);
mmput(mm);
return ret;
}
EXPORT_SYMBOL_GPL(copy_remote_vm_str);
#endif /* CONFIG_BPF_SYSCALL */
/*
* Print the name of a VMA.
*/

43
mm/nommu.c
View File

@ -1741,13 +1741,12 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
}
EXPORT_SYMBOL_GPL(access_process_vm);
#ifdef CONFIG_BPF_SYSCALL
/*
* Copy a string from another process's address space as given in mm.
* If there is any error return -EFAULT.
*/
static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len)
int __copy_remote_mm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
unsigned long addr_end;
struct vm_area_struct *vma;
@ -1782,44 +1781,6 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
return ret;
}
/**
* copy_remote_vm_str - copy a string from another process's address space.
* @tsk: the task of the target address space
* @addr: start address to read from
* @buf: destination buffer
* @len: number of bytes to copy
* @gup_flags: flags modifying lookup behaviour (unused)
*
* The caller must hold a reference on @mm.
*
* Return: number of bytes copied from @addr (source) to @buf (destination);
* not including the trailing NUL. Always guaranteed to leave NUL-terminated
* buffer. On any error, return -EFAULT.
*/
int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
struct mm_struct *mm;
int ret;
if (unlikely(len == 0))
return 0;
mm = get_task_mm(tsk);
if (!mm) {
*(char *)buf = '\0';
return -EFAULT;
}
ret = __copy_remote_vm_str(mm, addr, buf, len);
mmput(mm);
return ret;
}
EXPORT_SYMBOL_GPL(copy_remote_vm_str);
#endif /* CONFIG_BPF_SYSCALL */
/**
* nommu_shrink_inode_mappings - Shrink the shared mappings on an inode
* @inode: The inode to check

60
mm/util.c
View File

@ -1061,6 +1061,66 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
return res;
}
/**
* copy_remote_mm_str - copy a string from a remote address space.
* @mm: the remote address space
* @addr: start address to read from
* @buf: destination buffer
* @len: number of bytes to copy
* @gup_flags: flags modifying lookup behaviour
*
* The caller must hold a reference on @mm.
*
* Return: number of bytes copied from @addr (source) to @buf (destination),
* not including the trailing NUL. If @len is zero, return 0 without accessing
* @buf. Otherwise, @buf is always NUL-terminated. On any error, return
* -EFAULT.
*/
int copy_remote_mm_str(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
if (unlikely(len == 0))
return 0;
return __copy_remote_mm_str(mm, addr, buf, len, gup_flags);
}
/**
* copy_remote_vm_str - copy a string from another process's address space.
* @tsk: the task of the target address space
* @addr: start address to read from
* @buf: destination buffer
* @len: number of bytes to copy
* @gup_flags: flags modifying lookup behaviour
*
* Return: number of bytes copied from @addr (source) to @buf (destination),
* not including the trailing NUL. If @len is zero, return 0 without accessing
* @buf. Otherwise, @buf is always NUL-terminated. On any error, return
* -EFAULT.
*/
int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags)
{
struct mm_struct *mm;
int ret;
if (unlikely(len == 0))
return 0;
mm = get_task_mm(tsk);
if (!mm) {
*(char *)buf = '\0';
return -EFAULT;
}
ret = __copy_remote_mm_str(mm, addr, buf, len, gup_flags);
mmput(mm);
return ret;
}
EXPORT_SYMBOL_GPL(copy_remote_vm_str);
int __weak memcmp_pages(struct page *page1, struct page *page2)
{
char *addr1, *addr2;