[PATCH v2 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU

Jann Horn
2020-04-29T21:49:50Z

dump_emit() is for kernel pointers, and VMAs describe userspace memory.
Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS,
even if it probably doesn't matter much on !MMU systems - especially given
that it looks like we can just use the same get_dump_page() as on MMU if
we move it out of the CONFIG_MMU block.

Signed-off-by: Jann Horn <jannh@google.com>
---
fs/binfmt_elf_fdpic.c | 8 ------
mm/gup.c | 58 +++++++++++++++++++++----------------------
2 files changed, 29 insertions(+), 37 deletions(-)

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index c62c17a5c34a9..f5b47076fa762 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1495,14 +1495,11 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
struct vm_area_struct *vma;

for (vma = current->mm->mmap; vma; vma = vma->vm_next) {
-#ifdef CONFIG_MMU
unsigned long addr;
-#endif

if (!maydump(vma, cprm->mm_flags))
continue;

-#ifdef CONFIG_MMU
for (addr = vma->vm_start; addr < vma->vm_end;
addr += PAGE_SIZE) {
bool res;
@@ -1518,11 +1515,6 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
if (!res)
return false;
}
-#else
- if (!dump_emit(cprm, (void *) vma->vm_start,
- vma->vm_end - vma->vm_start))
- return false;
-#endif
}
return true;
}
diff --git a/mm/gup.c b/mm/gup.c
index 50681f0286ded..76080c4dbff05 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1490,35 +1490,6 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
up_read(&mm->mmap_sem);
return ret; /* 0 or negative error code */
}
-
-/**
- * get_dump_page() - pin user page in memory while writing it to core dump
- * @addr: user address
- *
- * Returns struct page pointer of user page pinned for dump,
- * to be freed afterwards by put_page().
- *
- * Returns NULL on any kind of failure - a hole must then be inserted into
- * the corefile, to preserve alignment with its headers; and also returns
- * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
- * allowing a hole to be left in the corefile to save diskspace.
- *
- * Called without mmap_sem, but after all other threads have been killed.
- */
-#ifdef CONFIG_ELF_CORE
-struct page *get_dump_page(unsigned long addr)
-{
- struct vm_area_struct *vma;
- struct page *page;
-
- if (__get_user_pages(current, current->mm, addr, 1,
- FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
- NULL) < 1)
- return NULL;
- flush_cache_page(vma, addr, page_to_pfn(page));
- return page;
-}
-#endif /* CONFIG_ELF_CORE */
#else /* CONFIG_MMU */
static long __get_user_pages_locked(struct task_struct *tsk,
struct mm_struct *mm, unsigned long start,
@@ -1565,6 +1536,35 @@ static long __get_user_pages_locked(struct task_struct *tsk,
}
#endif /* !CONFIG_MMU */

+/**
+ * get_dump_page() - pin user page in memory while writing it to core dump
+ * @addr: user address
+ *
+ * Returns struct page pointer of user page pinned for dump,
+ * to be freed afterwards by put_page().
+ *
+ * Returns NULL on any kind of failure - a hole must then be inserted into
+ * the corefile, to preserve alignment with its headers; and also returns
+ * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
+ * allowing a hole to be left in the corefile to save diskspace.
+ *
+ * Called without mmap_sem, but after all other threads have been killed.
+ */
+#ifdef CONFIG_ELF_CORE
+struct page *get_dump_page(unsigned long addr)
+{
+ struct vm_area_struct *vma;
+ struct page *page;
+
+ if (__get_user_pages(current, current->mm, addr, 1,
+ FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
+ NULL) < 1)
+ return NULL;
+ flush_cache_page(vma, addr, page_to_pfn(page));
+ return page;
+}
+#endif /* CONFIG_ELF_CORE */
+
#if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
{
--
2.26.2.526.g744177e7f7-goog