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Waiman Long
71368af902
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: Thomas Gleixner <[email protected]> Signed-off-by: Waiman Long <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Jonathan Corbet <[email protected]> Cc: [email protected] Cc: "H. Peter Anvin" <[email protected]> Cc: Andi Kleen <[email protected]> Cc: David Woodhouse <[email protected]> Cc: Jiri Kosina <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: Tim Chen <[email protected]> Cc: KarimAllah Ahmed <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Konrad Rzeszutek Wilk <[email protected]> Link: https://lkml.kernel.org/r/[email protected]