The patch titled Subject: mm: fix uprobe pte be overwritten when expanding vma has been added to the -mm mm-unstable branch. Its filename is mm-fix-uprobe-pte-be-overwritten-when-expanding-vma.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Pu Lehui pulehui@huawei.com Subject: mm: fix uprobe pte be overwritten when expanding vma Date: Thu, 29 May 2025 15:56:47 +0000

Patch series "Fix uprobe pte be overwritten when expanding vma".

This patch (of 4):

We encountered a BUG alert triggered by Syzkaller as follows: BUG: Bad rss-counter state mm:00000000b4a60fca type:MM_ANONPAGES val:1

And we can reproduce it with the following steps: 1. register uprobe on file at zero offset 2. mmap the file at zero offset: addr1 = mmap(NULL, 2 * 4096, PROT_NONE, MAP_PRIVATE, fd, 0); 3. mremap part of vma1 to new vma2: addr2 = mremap(addr1, 4096, 2 * 4096, MREMAP_MAYMOVE); 4. mremap back to orig addr1: mremap(addr2, 4096, 4096, MREMAP_MAYMOVE | MREMAP_FIXED, addr1);

In step 3, the vma1 range [addr1, addr1 + 4096] will be remap to new vma2 with range [addr2, addr2 + 8192], and remap uprobe anon page from the vma1 to vma2, then unmap the vma1 range [addr1, addr1 + 4096].

In step 4, the vma2 range [addr2, addr2 + 4096] will be remap back to the addr range [addr1, addr1 + 4096]. Since the addr range [addr1 + 4096, addr1 + 8192] still maps the file, it will take vma_merge_new_range to expand the range, and then do uprobe_mmap in vma_complete. Since the merged vma pgoff is also zero offset, it will install uprobe anon page to the merged vma. However, the upcomming move_page_tables step, which use set_pte_at to remap the vma2 uprobe pte to the merged vma, will overwrite the newly uprobe pte in the merged vma, and lead that pte to be orphan.

Since the uprobe pte will be remapped to the merged vma, we can remove the unnecessary uprobe_mmap upon merged vma.

This problem was first found in linux-6.6.y and also exists in the community syzkaller: https://lore.kernel.org/all/000000000000ada39605a5e71711@google.com/T/

Link: https://lkml.kernel.org/r/20250529155650.4017699-1-pulehui@huaweicloud.com Link: https://lkml.kernel.org/r/20250529155650.4017699-2-pulehui@huaweicloud.com Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints") Signed-off-by: Pu Lehui pulehui@huawei.com Suggested-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Jann Horn jannh@google.com Cc: Liam Howlett liam.howlett@oracle.com Cc: "Masami Hiramatsu (Google)" mhiramat@kernel.org Cc: Oleg Nesterov oleg@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/vma.c | 20 +++++++++++++++++--- mm/vma.h | 7 +++++++ 2 files changed, 24 insertions(+), 3 deletions(-)

--- a/mm/vma.c~mm-fix-uprobe-pte-be-overwritten-when-expanding-vma +++ a/mm/vma.c @@ -169,6 +169,9 @@ static void init_multi_vma_prep(struct v 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_prep

if (vp->file) { i_mmap_unlock_write(vp->mapping); - uprobe_mmap(vp->vma);

- if (vp->adj_next) - uprobe_mmap(vp->adj_next); + if (!vp->skip_vma_uprobe) { + 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 v 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 */ --- a/mm/vma.h~mm-fix-uprobe-pte-be-overwritten-when-expanding-vma +++ a/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: */

/* _

Patches currently in -mm which might be from pulehui@huawei.com are

mm-fix-uprobe-pte-be-overwritten-when-expanding-vma.patch mm-expose-abnormal-new_pte-during-move_ptes.patch selftests-mm-extract-read_sysfs-and-write_sysfs-into-vm_util.patch selftests-mm-add-test-about-uprobe-pte-be-orphan-during-vma-merge.patch