ARM: 8794/1: uaccess: Prevent speculative use of the current addr_limit

Commit 621afc677465db231662ed126ae1f355bf8eac47 upstream.

A mispredicted conditional call to set_fs could result in the wrong
addr_limit being forwarded under speculation to a subsequent access_ok
check, potentially forming part of a spectre-v1 attack using uaccess
routines.

This patch prevents this forwarding from taking place, but putting heavy
barriers in set_fs after writing the addr_limit.

Porting commit c2f0ad4fc089cff8 ("arm64: uaccess: Prevent speculative use
of the current addr_limit").

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David A. Long <dave.long@linaro.org>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index fd33021..0404dd1 100644 (file)
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -99,6 +99,14 @@ extern int __put_user_bad(void);
 static inline void set_fs(mm_segment_t fs)
 {
        current_thread_info()->addr_limit = fs;
+
+       /*
+        * Prevent a mispredicted conditional call to set_fs from forwarding
+        * the wrong address limit to access_ok under speculation.
+        */
+       dsb(nsh);
+       isb();
+
        modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER);
 }