From: Julien Thierry julien.thierry@arm.com
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 --- arch/arm/include/asm/uaccess.h | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h index 7b17460127fd..9ae888775743 100644 --- 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); }