x86: Add support for restartable sequences

Call the rseq_handle_notify_resume() function on return to userspace if
TIF_NOTIFY_RESUME thread flag is set.

Perform fixup on the pre-signal frame when a signal is delivered on top
of a restartable sequence critical section.

Check that system calls are not invoked from within rseq critical
sections by invoking rseq_signal() from syscall_return_slowpath().
With CONFIG_DEBUG_RSEQ, such behavior results in termination of the
process with SIGSEGV.

Signed-off-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dave Watson <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: "H . Peter Anvin" <[email protected]>
Cc: Chris Lameter <[email protected]>
Cc: Russell King <[email protected]>
Cc: Andrew Hunter <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: "Paul E . McKenney" <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Ben Maurer <[email protected]>
Cc: [email protected]
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index fbf6a6c3fd2d..92190879b228 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -164,6 +164,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_NOTIFY_RESUME) {
 			clear_thread_flag(TIF_NOTIFY_RESUME);
 			tracehook_notify_resume(regs);
+			rseq_handle_notify_resume(regs);
 		}
 
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
@@ -254,6 +255,8 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 	    WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 		local_irq_enable();
 
+	rseq_syscall(regs);
+
 	/*
 	 * First do one-time work.  If these work items are enabled, we
 	 * want to run them exactly once per syscall exit with IRQs on.