- The 4 patch series "Fix uprobe pte be overwritten when expanding vma"

fixes a longstanding and quite obscure bug related to the vma merging of
   the uprobe mmap page.
 -----BEGIN PGP SIGNATURE-----
 
 iHUEABYKAB0WIQTTMBEPP41GrTpTJgfdBJ7gKXxAjgUCaEN1LAAKCRDdBJ7gKXxA
 jsfLAQCC+C8397X6lNKPI3bHGLGEHubP2uzb6bOFMAU6fIRobQEAqUnoUhfP+xsu
 tDbcQEBZ+vfyeT9Zr9vA+uBDcA3OGw0=
 =9oaG
 -----END PGP SIGNATURE-----

Merge tag 'mm-stable-2025-06-06-16-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull more MM updates from Andrew Morton:
 "The series 'Fix uprobe pte be overwritten when expanding vma' fixes a
  longstanding and quite obscure bug related to the vma merging of the
  uprobe mmap page"

* tag 'mm-stable-2025-06-06-16-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm:
  selftests/mm: add test about uprobe pte be orphan during vma merge
  selftests/mm: extract read_sysfs and write_sysfs into vm_util
  mm: expose abnormal new_pte during move_ptes
  mm: fix uprobe pte be overwritten when expanding vma
  mm/damon: s/primitives/code/ on comments

mm/damon/modules-common.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Common Primitives for DAMON Modules
+ * Common Code for DAMON Modules
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/modules-common.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Common Primitives for DAMON Modules
+ * Common Code for DAMON Modules
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/ops-common.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Common Primitives for Data Access Monitoring
+ * Common Code for Data Access Monitoring
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/ops-common.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Common Primitives for Data Access Monitoring
+ * Common Code for Data Access Monitoring
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/paddr.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * DAMON Primitives for The Physical Address Space
+ * DAMON Code for The Physical Address Space
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/sysfs-common.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Common Primitives for DAMON Sysfs Interface
+ * Common Code for DAMON Sysfs Interface
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/sysfs-common.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Common Primitives for DAMON Sysfs Interface
+ * Common Code for DAMON Sysfs Interface
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/damon/vaddr.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * DAMON Primitives for Virtual Address Spaces
+ * DAMON Code for Virtual Address Spaces
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

mm/mremap.c

@@ -237,6 +237,8 @@ static int move_ptes(struct pagetable_move_control *pmc,
 
 	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 				   new_pte++, new_addr += PAGE_SIZE) {
+		VM_WARN_ON_ONCE(!pte_none(*new_pte));
+
 		if (pte_none(ptep_get(old_pte)))
 			continue;
 

mm/vma.c

@@ -169,6 +169,9 @@ static void init_multi_vma_prep(struct vma_prepare *vp,
 	vp->file = vma->vm_file;
 	if (vp->file)
 		vp->mapping = vma->vm_file->f_mapping;
+
+	if (vmg && vmg->skip_vma_uprobe)
+		vp->skip_vma_uprobe = true;
 }
 
 /*
@@ -358,10 +361,13 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi,
 
 	if (vp->file) {
 		i_mmap_unlock_write(vp->mapping);
-		uprobe_mmap(vp->vma);
 
-		if (vp->adj_next)
+		if (!vp->skip_vma_uprobe) {
-			uprobe_mmap(vp->adj_next);
+			uprobe_mmap(vp->vma);
+
+			if (vp->adj_next)
+				uprobe_mmap(vp->adj_next);
+		}
 	}
 
 	if (vp->remove) {
@@ -1830,6 +1836,14 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		faulted_in_anon_vma = false;
 	}
 
+	/*
+	 * If the VMA we are copying might contain a uprobe PTE, ensure
+	 * that we do not establish one upon merge. Otherwise, when mremap()
+	 * moves page tables, it will orphan the newly created PTE.
+	 */
+	if (vma->vm_file)
+		vmg.skip_vma_uprobe = true;
+
 	new_vma = find_vma_prev(mm, addr, &vmg.prev);
 	if (new_vma && new_vma->vm_start < addr + len)
 		return NULL;	/* should never get here */

mm/vma.h

@@ -19,6 +19,8 @@ struct vma_prepare {
 	struct vm_area_struct *insert;
 	struct vm_area_struct *remove;
 	struct vm_area_struct *remove2;
+
+	bool skip_vma_uprobe :1;
 };
 
 struct unlink_vma_file_batch {
@@ -120,6 +122,11 @@ struct vma_merge_struct {
 	 */
 	bool give_up_on_oom :1;
 
+	/*
+	 * If set, skip uprobe_mmap upon merged vma.
+	 */
+	bool skip_vma_uprobe :1;
+
 	/* Internal flags set during merge process: */
 
 	/*

tools/testing/selftests/mm/ksm_tests.c

@@ -58,40 +58,12 @@ int debug;
 
 static int ksm_write_sysfs(const char *file_path, unsigned long val)
 {
-	FILE *f = fopen(file_path, "w");
+	return write_sysfs(file_path, val);
-
-	if (!f) {
-		fprintf(stderr, "f %s\n", file_path);
-		perror("fopen");
-		return 1;
-	}
-	if (fprintf(f, "%lu", val) < 0) {
-		perror("fprintf");
-		fclose(f);
-		return 1;
-	}
-	fclose(f);
-
-	return 0;
 }
 
 static int ksm_read_sysfs(const char *file_path, unsigned long *val)
 {
-	FILE *f = fopen(file_path, "r");
+	return read_sysfs(file_path, val);
-
-	if (!f) {
-		fprintf(stderr, "f %s\n", file_path);
-		perror("fopen");
-		return 1;
-	}
-	if (fscanf(f, "%lu", val) != 1) {
-		perror("fscanf");
-		fclose(f);
-		return 1;
-	}
-	fclose(f);
-
-	return 0;
 }
 
 static void ksm_print_sysfs(void)

tools/testing/selftests/mm/merge.c

@@ -2,11 +2,14 @@
 
 #define _GNU_SOURCE
 #include "../kselftest_harness.h"
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 #include <sys/wait.h>
+#include <linux/perf_event.h>
 #include "vm_util.h"
 
 FIXTURE(merge)
@@ -452,4 +455,44 @@ TEST_F(merge, forked_source_vma)
 	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr2 + 5 * page_size);
 }
 
+TEST_F(merge, handle_uprobe_upon_merged_vma)
+{
+	const size_t attr_sz = sizeof(struct perf_event_attr);
+	unsigned int page_size = self->page_size;
+	const char *probe_file = "./foo";
+	char *carveout = self->carveout;
+	struct perf_event_attr attr;
+	unsigned long type;
+	void *ptr1, *ptr2;
+	int fd;
+
+	fd = open(probe_file, O_RDWR|O_CREAT, 0600);
+	ASSERT_GE(fd, 0);
+
+	ASSERT_EQ(ftruncate(fd, page_size), 0);
+	ASSERT_EQ(read_sysfs("/sys/bus/event_source/devices/uprobe/type", &type), 0);
+
+	memset(&attr, 0, attr_sz);
+	attr.size = attr_sz;
+	attr.type = type;
+	attr.config1 = (__u64)(long)probe_file;
+	attr.config2 = 0x0;
+
+	ASSERT_GE(syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0), 0);
+
+	ptr1 = mmap(&carveout[page_size], 10 * page_size, PROT_EXEC,
+		    MAP_PRIVATE | MAP_FIXED, fd, 0);
+	ASSERT_NE(ptr1, MAP_FAILED);
+
+	ptr2 = mremap(ptr1, page_size, 2 * page_size,
+		      MREMAP_MAYMOVE | MREMAP_FIXED, ptr1 + 5 * page_size);
+	ASSERT_NE(ptr2, MAP_FAILED);
+
+	ASSERT_NE(mremap(ptr2, page_size, page_size,
+			 MREMAP_MAYMOVE | MREMAP_FIXED, ptr1), MAP_FAILED);
+
+	close(fd);
+	remove(probe_file);
+}
+
 TEST_HARNESS_MAIN

tools/testing/selftests/mm/thuge-gen.c

@@ -77,7 +77,7 @@ void show(unsigned long ps)
 	system(buf);
 }
 
-unsigned long read_sysfs(int warn, char *fmt, ...)
+unsigned long thuge_read_sysfs(int warn, char *fmt, ...)
 {
 	char *line = NULL;
 	size_t linelen = 0;
@@ -106,7 +106,7 @@ unsigned long read_sysfs(int warn, char *fmt, ...)
 
 unsigned long read_free(unsigned long ps)
 {
-	return read_sysfs(ps != getpagesize(),
+	return thuge_read_sysfs(ps != getpagesize(),
 			  "/sys/kernel/mm/hugepages/hugepages-%lukB/free_hugepages",
 			  ps >> 10);
 }
@@ -195,7 +195,7 @@ void find_pagesizes(void)
 	}
 	globfree(&g);
 
-	if (read_sysfs(0, "/proc/sys/kernel/shmmax") < NUM_PAGES * largest)
+	if (thuge_read_sysfs(0, "/proc/sys/kernel/shmmax") < NUM_PAGES * largest)
 		ksft_exit_fail_msg("Please do echo %lu > /proc/sys/kernel/shmmax",
 				   largest * NUM_PAGES);
 

tools/testing/selftests/mm/vm_util.c

@@ -486,3 +486,41 @@ int close_procmap(struct procmap_fd *procmap)
 {
 	return close(procmap->fd);
 }
+
+int write_sysfs(const char *file_path, unsigned long val)
+{
+	FILE *f = fopen(file_path, "w");
+
+	if (!f) {
+		fprintf(stderr, "f %s\n", file_path);
+		perror("fopen");
+		return 1;
+	}
+	if (fprintf(f, "%lu", val) < 0) {
+		perror("fprintf");
+		fclose(f);
+		return 1;
+	}
+	fclose(f);
+
+	return 0;
+}
+
+int read_sysfs(const char *file_path, unsigned long *val)
+{
+	FILE *f = fopen(file_path, "r");
+
+	if (!f) {
+		fprintf(stderr, "f %s\n", file_path);
+		perror("fopen");
+		return 1;
+	}
+	if (fscanf(f, "%lu", val) != 1) {
+		perror("fscanf");
+		fclose(f);
+		return 1;
+	}
+	fclose(f);
+
+	return 0;
+}

tools/testing/selftests/mm/vm_util.h

@@ -88,6 +88,8 @@ int open_procmap(pid_t pid, struct procmap_fd *procmap_out);
 int query_procmap(struct procmap_fd *procmap);
 bool find_vma_procmap(struct procmap_fd *procmap, void *address);
 int close_procmap(struct procmap_fd *procmap);
+int write_sysfs(const char *file_path, unsigned long val);
+int read_sysfs(const char *file_path, unsigned long *val);
 
 static inline int open_self_procmap(struct procmap_fd *procmap_out)
 {