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 --- 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