On 2022-02-28 14:46, Kees Cook wrote:
Partially revert commit 5f501d555653 ("binfmt_elf: reintroduce using
MAP_FIXED_NOREPLACE").
At least ia64 has ET_EXEC PT_LOAD segments that are not virtual-address
contiguous (but _are_ file-offset contiguous). This would result in
giant mapping attempts to cover the entire span, including the virtual
address range hole. Disable total_mapping_size for ET_EXEC, which
reduces the MAP_FIXED_NOREPLACE coverage to only the first PT_LOAD:
$ readelf -lW /usr/bin/gcc
...
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz
...
...
LOAD 0x000000 0x4000000000000000 0x4000000000000000 0x00b5a0 0x00b5a0
...
LOAD 0x00b5a0 0x600000000000b5a0 0x600000000000b5a0 0x0005ac 0x000710
...
...
^^^^^^^^ ^^^^^^^^^^^^^^^^^^ ^^^^^^^^ ^^^^^^^^
File offset range : 0x000000-0x00bb4c
0x00bb4c bytes
Virtual address range : 0x4000000000000000-0x600000000000bcb0
0x200000000000bcb0 bytes
Ironically, this is the reverse of the problem that originally caused
problems with ET_EXEC and MAP_FIXED_NOREPLACE: overlaps. This problem
is
with holes. Future work could restore full coverage if
load_elf_binary()
were to perform mappings in a separate phase from the loading (where
it could resolve both overlaps and holes).
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Reported-by: matoro <matoro_mailinglist_kernel@xxxxxxxxx>
Reported-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
Fixes: 5f501d555653 ("binfmt_elf: reintroduce using
MAP_FIXED_NOREPLACE")
Link:
https://lore.kernel.org/r/a3edd529-c42d-3b09-135c-7e98a15b150f@xxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
matoro (or anyone else) can you please test this?
---
fs/binfmt_elf.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 9bea703ed1c2..474b44032c65 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1136,14 +1136,25 @@ static int load_elf_binary(struct linux_binprm
*bprm)
* is then page aligned.
*/
load_bias = ELF_PAGESTART(load_bias - vaddr);
- }
- /*
- * Calculate the entire size of the ELF mapping (total_size).
- * (Note that first_pt_load is set to false later once the
- * initial mapping is performed.)
- */
- if (first_pt_load) {
+ /*
+ * Calculate the entire size of the ELF mapping
+ * (total_size), used for the initial mapping,
+ * due to first_pt_load which is set to false later
+ * once the initial mapping is performed.
+ *
+ * Note that this is only sensible when the LOAD
+ * segments are contiguous (or overlapping). If
+ * used for LOADs that are far apart, this would
+ * cause the holes between LOADs to be mapped,
+ * running the risk of having the mapping fail,
+ * as it would be larger than the ELF file itself.
+ *
+ * As a result, only ET_DYN does this, since
+ * some ET_EXEC (e.g. ia64) may have virtual
+ * memory holes between LOADs.
+ *
+ */
total_size = total_mapping_size(elf_phdata,
elf_ex->e_phnum);
if (!total_size) {
This does not apply for me, I'm looking around and can't find any
reference to the first_pt_load variable you're removing there? What
commit/tag are you applying this on top of?
