[Devel] [PATCH hci-8.1 3/7] oracle/mm: keep a MADV_DOEXEC range from becoming executable

[Konstantin Khorenko <khorenko@virtuozzo.com>]

MADV_DOEXEC rejects executable memory and MADV_DONTEXEC gives
VM_MAYEXEC back, so the intent is that a preserved range cannot become
executable. Two bugs break it:

- The OR-assignment in the MADV_DOEXEC case never drops VM_MAYEXEC, so
  mprotect(PROT_EXEC) on the range succeeds and exec carries the
  executable mapping into the new image.
- MADV_DONTEXEC sets VM_MAYEXEC unconditionally. A private /dev/zero
  mapping from a noexec mount, which do_mmap() created without
  VM_MAYEXEC, becomes executable after MADV_DOEXEC and MADV_DONTEXEC.

Clear the bit on MADV_DOEXEC and give back what do_mmap() grants such a
mapping whenever the mark goes: on MADV_DONTEXEC, and when exec or fork
drops it from a copy, which could otherwise never be made executable
again.

Fixes: 056724255f5f ("oracle/mm: introduce MADV_DOEXEC")
https://virtuozzo.atlassian.net/browse/VSTOR-150232

Feature: oracle/mm: MADV_DOEXEC madvise() flag
Assisted-by: LLM
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 include/linux/mm.h |  1 +
 kernel/fork.c      |  4 +++-
 mm/madvise.c       |  5 +++--
 mm/mmap.c          | 13 ++++++++++++-
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9ebf3c6dcb978..91f305fd5c025 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2463,6 +2463,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
 		  unsigned long size);
 void zap_vma_mt(struct vm_area_struct *vma);
+vm_flags_t vma_doexec_mayexec(struct vm_area_struct *vma);
 void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
 			   unsigned long size, struct zap_details *details);
 static inline void zap_vma_pages(struct vm_area_struct *vma)
diff --git a/kernel/fork.c b/kernel/fork.c
index 92a7e9aae9278..25e87cdbeb073 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -715,7 +715,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 			tmp->anon_vma = NULL;
 		} else if (anon_vma_fork(tmp, mpnt))
 			goto fail_nomem_anon_vma_fork;
-		vm_flags_clear(tmp, VM_LOCKED_MASK | VM_EXEC_KEEP);
+		if (tmp->vm_flags & VM_EXEC_KEEP)
+			vm_flags_mod(tmp, vma_doexec_mayexec(tmp), VM_EXEC_KEEP);
+		vm_flags_clear(tmp, VM_LOCKED_MASK);
 		/*
 		 * Copy/update hugetlb private vma information.
 		 */
diff --git a/mm/madvise.c b/mm/madvise.c
index 644057a2bbbb0..e6972bcfc9749 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1318,7 +1318,7 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
 			error = -EINVAL;
 			goto out;
 		}
-		new_flags |= (new_flags & ~VM_MAYEXEC) | VM_EXEC_KEEP;
+		new_flags = (new_flags & ~VM_MAYEXEC) | VM_EXEC_KEEP;
 		break;
 	case MADV_DONTEXEC:
 		if (!VM_EXEC_KEEP) {
@@ -1326,7 +1326,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
 			goto out;
 		}
 		if (new_flags & VM_EXEC_KEEP)
-			new_flags = (new_flags & ~VM_EXEC_KEEP) | VM_MAYEXEC;
+			new_flags = (new_flags & ~VM_EXEC_KEEP) |
+				    vma_doexec_mayexec(vma);
 		break;
 	case MADV_DONTDUMP:
 		new_flags |= VM_DONTDUMP;
diff --git a/mm/mmap.c b/mm/mmap.c
index 52e971aee020f..69dd1514d750e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1750,6 +1750,17 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 	return 0;
 }
 
+/*
+ * The VM_MAYEXEC that MADV_DOEXEC took from @vma, to give back when the mark
+ * goes: what do_mmap() grants such a mapping.
+ */
+vm_flags_t vma_doexec_mayexec(struct vm_area_struct *vma)
+{
+	if (vma->vm_file && path_noexec(&vma->vm_file->f_path))
+		return 0;
+	return VM_MAYEXEC;
+}
+
 /*
  * Duplicate an anonymous VMA into a new mm as part of preserving
  * it across exec.
@@ -1811,7 +1822,7 @@ int vma_dup(struct vm_area_struct *old_vma, struct mm_struct *mm)
 #else
 	ret = copy_page_range(vma, old_vma);
 #endif
-	vm_flags_clear(vma, VM_EXEC_KEEP);
+	vm_flags_mod(vma, vma_doexec_mayexec(vma), VM_EXEC_KEEP);
 
 	return ret;
 

-- 
2.43.0

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