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 <[email protected]> --- 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
