From: Will Deacon <[email protected]> commit c2f0ad4fc089 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 <[email protected]> Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Catalin Marinas <[email protected]> Signed-off-by: Alex Shi <[email protected]> Conflicts: no set_thread_flag(TIF_FSCHECK) in arch/arm64/include/asm/uaccess.h --- 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 3531fec..00025c5 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -71,6 +71,13 @@ 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. */ -- 2.7.4
