[PATCH v15 08/13] arch/arm64: enable task isolation functionality

[Chris Metcalf <cmetcalf@mellanox.com>]

In do_notify_resume(), call task_isolation_ready() for
TIF_TASK_ISOLATION tasks when we are checking the thread-info flags;
and after we've handled the other work, call task_isolation_enter()
for such tasks.  To ensure we always call task_isolation_enter() when
returning to userspace, add _TIF_TASK_ISOLATION to _TIF_WORK_MASK,
while leaving the old bitmask value as _TIF_WORK_LOOP_MASK to
check while looping.

We tweak syscall_trace_enter() slightly to carry the "flags"
value from current_thread_info()->flags for each of the tests,
rather than doing a volatile read from memory for each one.  This
avoids a small overhead for each test, and in particular avoids
that overhead for TIF_NOHZ when TASK_ISOLATION is not enabled.

We instrument the smp_send_reschedule() routine so that it checks for
isolated tasks and generates a suitable warning if we are about
to disturb one of them in strict or debug mode.

Finally, report on page faults in task-isolation processes in
do_page_faults().

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 arch/arm64/Kconfig                   |  1 +
 arch/arm64/include/asm/thread_info.h |  5 ++++-
 arch/arm64/kernel/ptrace.c           | 18 +++++++++++++++---
 arch/arm64/kernel/signal.c           | 10 ++++++++++
 arch/arm64/kernel/smp.c              |  2 ++
 arch/arm64/mm/fault.c                |  8 +++++++-
 6 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index bc3f00f586f1..5cacf1de28ae 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -62,6 +62,7 @@ config ARM64
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_TASK_ISOLATION
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARM_SMCCC
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index abd64bd1f6d9..bdc6426b9968 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -109,6 +109,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NEED_RESCHED	1
 #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
 #define TIF_FOREIGN_FPSTATE	3	/* CPU's FP state is not current's */
+#define TIF_TASK_ISOLATION	4
 #define TIF_NOHZ		7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_SYSCALL_AUDIT	9
@@ -124,6 +125,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_FOREIGN_FPSTATE	(1 << TIF_FOREIGN_FPSTATE)
+#define _TIF_TASK_ISOLATION	(1 << TIF_TASK_ISOLATION)
 #define _TIF_NOHZ		(1 << TIF_NOHZ)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
@@ -132,7 +134,8 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 
 #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
-				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE)
+				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
+				 _TIF_TASK_ISOLATION)
 
 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index e0c81da60f76..9f093fcf97a3 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -37,6 +37,7 @@
 #include <linux/regset.h>
 #include <linux/tracehook.h>
 #include <linux/elf.h>
+#include <linux/isolation.h>
 
 #include <asm/compat.h>
 #include <asm/debug-monitors.h>
@@ -1347,14 +1348,25 @@ static void tracehook_report_syscall(struct pt_regs *regs,
 
 asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 {
-	if (test_thread_flag(TIF_SYSCALL_TRACE))
+	unsigned long work = ACCESS_ONCE(current_thread_info()->flags);
+
+	if (work & _TIF_SYSCALL_TRACE)
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
 
-	/* Do the secure computing after ptrace; failures should be fast. */
+	/*
+	 * In task isolation mode, we may prevent the syscall from
+	 * running, and if so we also deliver a signal to the process.
+	 */
+	if (work & _TIF_TASK_ISOLATION) {
+		if (task_isolation_syscall(regs->syscallno) == -1)
+			return -1;
+	}
+
+	/* Do the secure computing check early; failures should be fast. */
 	if (secure_computing(NULL) == -1)
 		return -1;
 
-	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+	if (work & _TIF_SYSCALL_TRACEPOINT)
 		trace_sys_enter(regs, regs->syscallno);
 
 	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 404dd67080b9..f9b9b25636ca 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -25,6 +25,7 @@
 #include <linux/uaccess.h>
 #include <linux/tracehook.h>
 #include <linux/ratelimit.h>
+#include <linux/isolation.h>
 
 #include <asm/debug-monitors.h>
 #include <asm/elf.h>
@@ -424,9 +425,18 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)
 				fpsimd_restore_current_state();
+
+			if (thread_flags & _TIF_TASK_ISOLATION)
+				task_isolation_enter();
 		}
 
 		local_irq_disable();
 		thread_flags = READ_ONCE(current_thread_info()->flags);
+
+		/* Clear task isolation from cached_flags manually. */
+		if ((thread_flags & _TIF_TASK_ISOLATION) &&
+		    task_isolation_ready())
+			thread_flags &= ~_TIF_TASK_ISOLATION;
+
 	} while (thread_flags & _TIF_WORK_MASK);
 }
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d93d43352504..08b0f3754e85 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -37,6 +37,7 @@
 #include <linux/completion.h>
 #include <linux/of.h>
 #include <linux/irq_work.h>
+#include <linux/isolation.h>
 
 #include <asm/alternative.h>
 #include <asm/atomic.h>
@@ -874,6 +875,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
 
 void smp_send_reschedule(int cpu)
 {
+	task_isolation_debug(cpu, "reschedule IPI");
 	smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
 }
 
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 05d2bd776c69..784817478535 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -29,6 +29,7 @@
 #include <linux/sched.h>
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
+#include <linux/isolation.h>
 
 #include <asm/cpufeature.h>
 #include <asm/exception.h>
@@ -392,8 +393,13 @@ retry:
 	 * Handle the "normal" case first - VM_FAULT_MAJOR
 	 */
 	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
-			      VM_FAULT_BADACCESS))))
+			      VM_FAULT_BADACCESS)))) {
+		/* No signal was generated, but notify task-isolation tasks. */
+		if (user_mode(regs))
+			task_isolation_quiet_exception("page fault at %#lx",
+						       addr);
 		return 0;
+	}
 
 	/*
 	 * If we are in kernel mode at this point, we have no context to
-- 
2.7.2