Currently the mmap(MAP_FIXED) discards the overlapping part of the
existing VMA(s).
Introduce the new MAP_DONTUNMAP flag which forces the mmap to fail
with ENOMEM whenever the overlapping occurs and MAP_FIXED is set.
No existing mapping(s) is discarded.
The implementation tests the MAP_DONTUNMAP flag right before unmapping
the VMA. The tile arch is the dependency of mmap_flags.
I did the isolated tests and also tested it with Gentoo full
installation.
Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@xxxxxxxxx>
---
arch/tile/mm/elf.c | 1 +
include/linux/mm.h | 3 ++-
include/uapi/asm-generic/mman-common.h | 1 +
mm/mmap.c | 10 +++++++---
4 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 6225cc9..dae4b33 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -142,6 +142,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
if (!retval) {
unsigned long addr = MEM_USER_INTRPT;
addr = mmap_region(NULL, addr, INTRPT_SIZE,
+ MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
VM_READ|VM_EXEC|
VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
if (addr > (unsigned long) -PAGE_SIZE)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ed6407d..31dcdfb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2048,7 +2048,8 @@ extern int install_special_mapping(struct mm_struct *mm,
extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
extern unsigned long mmap_region(struct file *file, unsigned long addr,
- unsigned long len, vm_flags_t vm_flags, unsigned long pgoff);
+ unsigned long len, unsigned long mmap_flags,
+ vm_flags_t vm_flags, unsigned long pgoff);
extern unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long len, unsigned long prot, unsigned long flags,
vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate);
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 5827438..3655be3 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -19,6 +19,7 @@
#define MAP_TYPE 0x0f /* Mask for type of mapping */
#define MAP_FIXED 0x10 /* Interpret addr exactly */
#define MAP_ANONYMOUS 0x20 /* don't use a file */
+#define MAP_DONTUNMAP 0x40 /* don't unmap overlapping VMA */
#ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED
# define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be uninitialized */
#else
diff --git a/mm/mmap.c b/mm/mmap.c
index bd2e1a53..ab429c3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1286,7 +1286,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
vm_flags |= VM_NORESERVE;
}
- addr = mmap_region(file, addr, len, vm_flags, pgoff);
+ addr = mmap_region(file, addr, len, flags, vm_flags, pgoff);
if (!IS_ERR_VALUE(addr) &&
((vm_flags & VM_LOCKED) ||
(flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
@@ -1422,7 +1422,8 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
}
unsigned long mmap_region(struct file *file, unsigned long addr,
- unsigned long len, vm_flags_t vm_flags, unsigned long pgoff)
+ unsigned long len, unsigned long mmap_flags,
+ vm_flags_t vm_flags, unsigned long pgoff)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev;
@@ -1448,7 +1449,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
/* Clear old maps */
while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
&rb_parent)) {
- if (do_munmap(mm, addr, len))
+ const bool dont_unmap =
+ (mmap_flags & (MAP_DONTUNMAP | MAP_FIXED))
+ == (MAP_DONTUNMAP | MAP_FIXED);
+ if (dont_unmap || do_munmap(mm, addr, len))
return -ENOMEM;
}
--
2.7.4
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