[RFC bpf-next 3/9] mm: Expose locked mprotect operation

[Jiri Olsa <jolsa@kernel.org>]

The bpf_user_page_exec() in following patch needs to change page
protections while holding current->mm's mmap write lock.

Exposing the do_mprotect_pkey_locked helper for that.

Assisted-by: Codex:GPT-6
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/mm.h |  3 +++
 mm/mprotect.c      | 20 +++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 63f40e615754..47e853093601 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3435,6 +3435,9 @@ extern long change_protection(struct mmu_gather *tlb,
 extern int mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
 	  struct vm_area_struct *vma, struct vm_area_struct **pprev,
 	  unsigned long start, unsigned long end, vm_flags_t newflags);
+/* Caller must hold current->mm's mmap write lock. */
+int do_mprotect_pkey_locked(unsigned long start, size_t len,
+			    unsigned long prot, int pkey);
 
 /*
  * doesn't attempt to fault and will return short.
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2888ee638d87..8d800830d3e1 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -868,8 +868,8 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
 /*
  * pkey==-1 when doing a legacy mprotect()
  */
-static int do_mprotect_pkey(unsigned long start, size_t len,
-		unsigned long prot, int pkey)
+int do_mprotect_pkey_locked(unsigned long start, size_t len,
+			    unsigned long prot, int pkey)
 {
 	unsigned long nstart, end, tmp, reqprot;
 	struct vm_area_struct *vma, *prev;
@@ -899,8 +899,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 
 	reqprot = prot;
 
-	if (mmap_write_lock_killable(current->mm))
-		return -EINTR;
+	mmap_assert_write_locked(current->mm);
 
 	/*
 	 * If userspace did not allocate the pkey, do not let
@@ -1013,10 +1012,21 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		error = -ENOMEM;
 
 out:
-	mmap_write_unlock(current->mm);
 	return error;
 }
 
+static int do_mprotect_pkey(unsigned long start, size_t len,
+			    unsigned long prot, int pkey)
+{
+	int ret;
+
+	if (mmap_write_lock_killable(current->mm))
+		return -EINTR;
+	ret = do_mprotect_pkey_locked(start, len, prot, pkey);
+	mmap_write_unlock(current->mm);
+	return ret;
+}
+
 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 		unsigned long, prot)
 {
-- 
2.54.0