Subject: [PATCH for-stable-v4.4 35/53] ARM: oabi-compat: copy semops using __copy_from_user()

From: Ard Biesheuvel <[email-masked]>
Date: Tue, 5 Nov 2019 21:58:28 +0100

From: Russell King <[email-masked]>

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 <[email-masked]>
Signed-off-by: Russell King <[email-masked]>
Signed-off-by: David A. Long <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 arch/arm/kernel/sys_oabi-compat.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c
index 5f221acd21ae..640748e27035 100644
--- 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 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) {
-- 
2.17.1

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