[PATCH 05/14] x86: Add support for restartable sequences (v2)

From: Mathieu Desnoyers
Date: Mon Apr 30 2018 - 18:44:57 EST


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 <mathieu.desnoyers@xxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Russell King <linux@xxxxxxxxxxxxxxxx>
CC: Catalin Marinas <catalin.marinas@xxxxxxx>
CC: Will Deacon <will.deacon@xxxxxxx>
CC: Paul Turner <pjt@xxxxxxxxxx>
CC: Andrew Hunter <ahh@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
CC: Dave Watson <davejwatson@xxxxxx>
CC: Chris Lameter <cl@xxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Ben Maurer <bmaurer@xxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Boqun Feng <boqun.feng@xxxxxxxxx>
CC: linux-api@xxxxxxxxxxxxxxx

---

Changes since v1:
- Call rseq_signal() when returning from a system call.
---
arch/x86/Kconfig | 1 +
arch/x86/entry/common.c | 3 +++
arch/x86/kernel/signal.c | 6 ++++++
3 files changed, 10 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c07f492b871a..62e00a1a7cf7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -180,6 +180,7 @@ config X86
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE if X86_64 && UNWINDER_FRAME_POINTER && STACK_VALIDATION
select HAVE_STACK_VALIDATION if X86_64
+ select HAVE_RSEQ
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_UNSTABLE_SCHED_CLOCK
select HAVE_USER_RETURN_NOTIFIER
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.
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index da270b95fe4d..445ca11ff863 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -688,6 +688,12 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
sigset_t *set = sigmask_to_save();
compat_sigset_t *cset = (compat_sigset_t *) set;

+ /*
+ * Increment event counter and perform fixup for the pre-signal
+ * frame.
+ */
+ rseq_signal_deliver(regs);
+
/* Set up the stack frame */
if (is_ia32_frame(ksig)) {
if (ksig->ka.sa.sa_flags & SA_SIGINFO)
--
2.11.0