4.9-stable review patch. If anyone has any objections, please let me know.
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From: Russell King rmk+kernel@armlinux.org.uk
Commit 8c8484a1c18e3231648f5ba7cc5ffb7fd70b3ca4 upstream.
__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 Signed-off-by: David A. Long dave.long@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm/kernel/sys_oabi-compat.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/arch/arm/kernel/sys_oabi-compat.c +++ b/arch/arm/kernel/sys_oabi-compat.c @@ -328,9 +328,11 @@ asmlinkage long sys_oabi_semtimedop(int 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) {