ARM: oabi-compat: copy semops using __copy_from_user()

__get_user_error() is used as a fast accessor to make copying structure
members as efficient as possible.  However, with software PAN and the
recent Spectre variant 1, the efficiency is reduced as these are no
longer fast accessors.

In the case of software PAN, it has to switch the domain register around
each access, and with Spectre variant 1, it would have to repeat the
access_ok() check for each access.

Rather than using __get_user_error() to copy each semops element member,
copy each semops element in full using __copy_from_user().

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c
index b9786f491873fae6a2f448e85b3fd76eb7511665..4abe4909417fd311c9e3b035248ecdcb69a4d0f1 100644 (file)
--- a/arch/arm/kernel/sys_oabi-compat.c
+++ b/arch/arm/kernel/sys_oabi-compat.c
@@ -329,9 +329,11 @@ asmlinkage long sys_oabi_semtimedop(int semid,
                return -ENOMEM;
        err = 0;
        for (i = 0; i < nsops; i++) {
-               __get_user_error(sops[i].sem_num, &tsops->sem_num, err);
-               __get_user_error(sops[i].sem_op,  &tsops->sem_op,  err);
-               __get_user_error(sops[i].sem_flg, &tsops->sem_flg, err);
+               struct oabi_sembuf osb;
+               err |= __copy_from_user(&osb, tsops, sizeof(osb));
+               sops[i].sem_num = osb.sem_num;
+               sops[i].sem_op = osb.sem_op;
+               sops[i].sem_flg = osb.sem_flg;
                tsops++;
        }
        if (timeout) {