• Waiman Long's avatar
    x86/speculation: Add PR_SPEC_DISABLE_NOEXEC · 71368af9
    Waiman Long authored
    With the default SPEC_STORE_BYPASS_SECCOMP/SPEC_STORE_BYPASS_PRCTL mode,
    the TIF_SSBD bit will be inherited when a new task is fork'ed or cloned.
    It will also remain when a new program is execve'ed.
    
    Only certain class of applications (like Java) that can run on behalf of
    multiple users on a single thread will require disabling speculative store
    bypass for security purposes. Those applications will call prctl(2) at
    startup time to disable SSB. They won't rely on the fact the SSB might have
    been disabled. Other applications that don't need SSBD will just move on
    without checking if SSBD has been turned on or not.
    
    The fact that the TIF_SSBD is inherited across execve(2) boundary will
    cause performance of applications that don't need SSBD but their
    predecessors have SSBD on to be unwittingly impacted especially if they
    write to memory a lot.
    
    To remedy this problem, a new PR_SPEC_DISABLE_NOEXEC argument for the
    PR_SET_SPECULATION_CTRL option of prctl(2) is added to allow applications
    to specify that the SSBD feature bit on the task structure should be
    cleared whenever a new program is being execve'ed.
    Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarWaiman Long <longman@redhat.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Jonathan Corbet <corbet@lwn.net>
    Cc: linux-doc@vger.kernel.org
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: David Woodhouse <dwmw@amazon.co.uk>
    Cc: Jiri Kosina <jikos@kernel.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Cc: KarimAllah Ahmed <karahmed@amazon.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Link: https://lkml.kernel.org/r/1547676096-3281-1-git-send-email-longman@redhat.com
    71368af9
spec_ctrl.rst 4.46 KB