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

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__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>
This commit is contained in:
Russell King 2018-07-09 10:20:06 +01:00
parent 42019fc50d
commit 8c8484a1c1
1 changed files with 5 additions and 3 deletions
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8
arch/arm/kernel/sys_oabi-compat.c
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@ -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) {