From: Will Deacon will.deacon@arm.com
commit c2f0ad4fc089cff81cef6a13d04b399980ecbfcc 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.
Reviewed-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] --- arch/arm64/include/asm/uaccess.h | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index a9db051b967f..900397e73fa6 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -68,6 +68,13 @@ 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(); + + /* * Enable/disable UAO so that copy_to_user() etc can access * kernel memory with the unprivileged instructions. */