[PATCH bpf-next v9 1/5] mm: Add copy_remote_mm_str()
From: Anastasios Papagiannis
Date: Fri Sep 18 2026 - 09:27:07 EST
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@xxxxxxxxx>
Acked-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
include/linux/mm.h | 8 +++----
mm/internal.h | 3 +++
mm/memory.c | 43 ++-------------------------------
mm/nommu.c | 43 ++-------------------------------
mm/util.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 71 insertions(+), 86 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index dd09c438fa23..63f40e615754 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -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,
diff --git a/mm/internal.h b/mm/internal.h
index 38b1165212c9..7c326965a94f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -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;
diff --git a/mm/memory.c b/mm/memory.c
index 8b0c2c735d3d..fa819a8a1df6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -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.
*/
diff --git a/mm/nommu.c b/mm/nommu.c
index 498e01ee40b0..68b05565e15a 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -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
diff --git a/mm/util.c b/mm/util.c
index bf0513d1d3d0..75c0fc2061aa 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -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;
--
2.55.0