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authorOleg Nesterov <oleg@redhat.com>2015-09-09 00:58:31 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-09 01:35:28 +0300
commit8a9cc3b55e9d20289cc18a65257e62c2dd4932fb (patch)
treede51c41b04a41ba08d3fcd87e561b415975d2f27 /mm/mmap.c
parentb5330628546616af14ff23075fbf8d4ad91f6e25 (diff)
downloadlinux-8a9cc3b55e9d20289cc18a65257e62c2dd4932fb.tar.xz
mmap: fix the usage of ->vm_pgoff in special_mapping paths
Test-case: #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <sys/mman.h> #include <assert.h> void *find_vdso_vaddr(void) { FILE *perl; char buf[32] = {}; perl = popen("perl -e 'open STDIN,qq|/proc/@{[getppid]}/maps|;" "/^(.*?)-.*vdso/ && print hex $1 while <>'", "r"); fread(buf, sizeof(buf), 1, perl); fclose(perl); return (void *)atol(buf); } #define PAGE_SIZE 4096 int main(void) { void *vdso = find_vdso_vaddr(); assert(vdso); // of course they should differ, and they do so far printf("vdso pages differ: %d\n", !!memcmp(vdso, vdso + PAGE_SIZE, PAGE_SIZE)); // split into 2 vma's assert(mprotect(vdso, PAGE_SIZE, PROT_READ) == 0); // force another fault on the next check assert(madvise(vdso, 2 * PAGE_SIZE, MADV_DONTNEED) == 0); // now they no longer differ, the 2nd vm_pgoff is wrong printf("vdso pages differ: %d\n", !!memcmp(vdso, vdso + PAGE_SIZE, PAGE_SIZE)); return 0; } Output: vdso pages differ: 1 vdso pages differ: 0 This is because split_vma() correctly updates ->vm_pgoff, but the logic in insert_vm_struct() and special_mapping_fault() is absolutely broken, so the fault at vdso + PAGE_SIZE return the 1st page. The same happens if you simply unmap the 1st page. special_mapping_fault() does: pgoff = vmf->pgoff - vma->vm_pgoff; and this is _only_ correct if vma->vm_start mmaps the first page from ->vm_private_data array. vdso or any other user of install_special_mapping() is not anonymous, it has the "backing storage" even if it is just the array of pages. So we actually need to make vm_pgoff work as an offset in this array. Note: this also allows to fix another problem: currently gdb can't access "[vvar]" memory because in this case special_mapping_fault() doesn't work. Now that we can use ->vm_pgoff we can implement ->access() and fix this. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Pavel Emelyanov <xemul@parallels.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c12
1 files changed, 2 insertions, 10 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 82db4fc0a9d3..52b2f6e16f6f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2884,7 +2884,7 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
* using the existing file pgoff checks and manipulations.
* Similarly in do_mmap_pgoff and in do_brk.
*/
- if (!vma->vm_file) {
+ if (vma_is_anonymous(vma)) {
BUG_ON(vma->anon_vma);
vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
}
@@ -3027,21 +3027,13 @@ static int special_mapping_fault(struct vm_area_struct *vma,
pgoff_t pgoff;
struct page **pages;
- /*
- * special mappings have no vm_file, and in that case, the mm
- * uses vm_pgoff internally. So we have to subtract it from here.
- * We are allowed to do this because we are the mm; do not copy
- * this code into drivers!
- */
- pgoff = vmf->pgoff - vma->vm_pgoff;
-
if (vma->vm_ops == &legacy_special_mapping_vmops)
pages = vma->vm_private_data;
else
pages = ((struct vm_special_mapping *)vma->vm_private_data)->
pages;
- for (; pgoff && *pages; ++pages)
+ for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
pgoff--;
if (*pages) {