[PATCH v2 3/5] coredump: Refactor page range dumping into common helper

Jann Horn
2020-04-29T21:49:52Z

Both fs/binfmt_elf.c and fs/binfmt_elf_fdpic.c need to dump ranges of pages
into the coredump file. Extract that logic into a common helper.

Any other binfmt that actually wants to create coredumps will probably need
the same function; so stop making get_dump_page() depend on
CONFIG_ELF_CORE.

Signed-off-by: Jann Horn <jannh@google.com>
---
fs/binfmt_elf.c | 22 ++--------------------
fs/binfmt_elf_fdpic.c | 18 +++---------------
fs/coredump.c | 33 +++++++++++++++++++++++++++++++++
include/linux/coredump.h | 2 ++
mm/gup.c | 2 --
5 files changed, 40 insertions(+), 37 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index b29b84595b09f..fb36469848323 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2323,26 +2323,8 @@ static int elf_core_dump(struct coredump_params *cprm)

for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
vma = next_vma(vma, gate_vma)) {
- unsigned long addr;
- unsigned long end;
-
- end = vma->vm_start + vma_filesz[i++];
-
- for (addr = vma->vm_start; addr < end; addr += PAGE_SIZE) {
- struct page *page;
- int stop;
-
- page = get_dump_page(addr);
- if (page) {
- void *kaddr = kmap(page);
- stop = !dump_emit(cprm, kaddr, PAGE_SIZE);
- kunmap(page);
- put_page(page);
- } else
- stop = !dump_skip(cprm, PAGE_SIZE);
- if (stop)
- goto cleanup;
- }
+ if (!dump_user_range(cprm, vma->vm_start, vma_filesz[i++]))
+ goto cleanup;
}
dump_truncate(cprm);

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index f5b47076fa762..938f66f4de9b2 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1500,21 +1500,9 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
if (!maydump(vma, cprm->mm_flags))
continue;

- for (addr = vma->vm_start; addr < vma->vm_end;
- addr += PAGE_SIZE) {
- bool res;
- struct page *page = get_dump_page(addr);
- if (page) {
- void *kaddr = kmap(page);
- res = dump_emit(cprm, kaddr, PAGE_SIZE);
- kunmap(page);
- put_page(page);
- } else {
- res = dump_skip(cprm, PAGE_SIZE);
- }
- if (!res)
- return false;
- }
+ if (!dump_user_range(cprm, vma->vm_start,
+ vma->vma_end - vma->vm_start))
+ return false;
}
return true;
}
diff --git a/fs/coredump.c b/fs/coredump.c
index d6fcc36a7db1f..88f625eecaac1 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -859,6 +859,39 @@ int dump_skip(struct coredump_params *cprm, size_t nr)
}
EXPORT_SYMBOL(dump_skip);

+#ifdef CONFIG_ELF_CORE
+int dump_user_range(struct coredump_params *cprm, unsigned long start,
+ unsigned long len)
+{
+ unsigned long addr;
+
+ for (addr = start; addr < start + len; addr += PAGE_SIZE) {
+ struct page *page;
+ int stop;
+
+ /*
+ * To avoid having to allocate page tables for virtual address
+ * ranges that have never been used yet, use a helper that
+ * returns NULL when encountering an empty page table entry that
+ * would otherwise have been filled with the zero page.
+ */
+ page = get_dump_page(addr);
+ if (page) {
+ void *kaddr = kmap(page);
+
+ stop = !dump_emit(cprm, kaddr, PAGE_SIZE);
+ kunmap(page);
+ put_page(page);
+ } else {
+ stop = !dump_skip(cprm, PAGE_SIZE);
+ }
+ if (stop)
+ return 0;
+ }
+ return 1;
+}
+#endif
+
int dump_align(struct coredump_params *cprm, int align)
{
unsigned mod = cprm->pos & (align - 1);
diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index abf4b4e65dbb9..4289dc21c04ff 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -16,6 +16,8 @@ extern int dump_skip(struct coredump_params *cprm, size_t nr);
extern int dump_emit(struct coredump_params *cprm, const void *addr, int nr);
extern int dump_align(struct coredump_params *cprm, int align);
extern void dump_truncate(struct coredump_params *cprm);
+int dump_user_range(struct coredump_params *cprm, unsigned long start,
+ unsigned long len);
#ifdef CONFIG_COREDUMP
extern void do_coredump(const kernel_siginfo_t *siginfo);
#else
diff --git a/mm/gup.c b/mm/gup.c
index 76080c4dbff05..9a7e83772f1fe 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1550,7 +1550,6 @@ static long __get_user_pages_locked(struct task_struct *tsk,
*
* 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;
@@ -1563,7 +1562,6 @@ struct page *get_dump_page(unsigned long addr)
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