The results of "access_ok()" can be mis-speculated. The result is that
you can end speculatively:
if (access_ok(from, size))
// Right here
For the same reason as done in copy_from_user() by
commit 74e19ef0ff80 ("uaccess: Add speculation barrier to
copy_from_user()"), add a speculation barrier to copy_from_user_iter().
See commit 74e19ef0ff80 ("uaccess: Add speculation barrier to
copy_from_user()") for more details.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
lib/iov_iter.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 48bd0cbce8c2..8d08b3435174 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -49,11 +49,19 @@ size_t copy_from_user_iter(void __user *iter_from, size_t progress,
if (should_fail_usercopy())
return len;
- if (can_do_masked_user_access())
+ if (can_do_masked_user_access()) {
iter_from = mask_user_address(iter_from);
- else if (!access_ok(iter_from, len))
- return res;
+ } else {
+ if (!access_ok(iter_from, len))
+ return res;
+ /*
+ * Ensure that bad access_ok() speculation will not
+ * lead to nasty side effects *after* the copy is
+ * finished:
+ */
+ barrier_nospec();
+ }
to += progress;
instrument_copy_from_user_before(to, iter_from, len);
res = raw_copy_from_user(to, iter_from, len);
--
2.49.0
