linux-kernel - [PATCH 4.4 55/75] ARM: oabi-compat: copy semops using __copy_from

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Date:   Fri,  8 Nov 2019 19:50:12 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linus.walleij@...aro.org, rmk+kernel@...linux.org.uk, Ard Biesheuvel" 
        <ardb@...nel.org>, Mark Rutland <mark.rutland@....com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        "David A. Long" <dave.long@...aro.org>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH 4.4 55/75] ARM: oabi-compat: copy semops using __copy_from_user()

From: Russell King <rmk+kernel@...linux.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@....com>
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: David A. Long <dave.long@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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) {