x86/entry: Move C entry and exit code to arch/x86/entry/common.c

The entry and exit C helpers were confusingly scattered between
ptrace.c and signal.c, even though they aren't specific to
ptrace or signal handling.  Move them together in a new file.

This change just moves code around.  It doesn't change anything.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/324d686821266544d8572423cc281f961da445f4.1435952415.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/Makefile

@@ -2,6 +2,7 @@
 # Makefile for the x86 low level entry code
 #
 obj-y				:= entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
+obj-y				+= common.o
 
 obj-y				+= vdso/
 obj-y				+= vsyscall/

arch/x86/entry/common.c

@@ -0,0 +1,253 @@
+/*
+ * common.c - C code for kernel entry and exit
+ * Copyright (c) 2015 Andrew Lutomirski
+ * GPL v2
+ *
+ * Based on asm and ptrace code by many authors.  The code here originated
+ * in ptrace.c and signal.c.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/errno.h>
+#include <linux/ptrace.h>
+#include <linux/tracehook.h>
+#include <linux/audit.h>
+#include <linux/seccomp.h>
+#include <linux/signal.h>
+#include <linux/export.h>
+#include <linux/context_tracking.h>
+#include <linux/user-return-notifier.h>
+#include <linux/uprobes.h>
+
+#include <asm/desc.h>
+#include <asm/traps.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
+static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
+{
+#ifdef CONFIG_X86_64
+	if (arch == AUDIT_ARCH_X86_64) {
+		audit_syscall_entry(regs->orig_ax, regs->di,
+				    regs->si, regs->dx, regs->r10);
+	} else
+#endif
+	{
+		audit_syscall_entry(regs->orig_ax, regs->bx,
+				    regs->cx, regs->dx, regs->si);
+	}
+}
+
+/*
+ * We can return 0 to resume the syscall or anything else to go to phase
+ * 2.  If we resume the syscall, we need to put something appropriate in
+ * regs->orig_ax.
+ *
+ * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
+ * are fully functional.
+ *
+ * For phase 2's benefit, our return value is:
+ * 0:			resume the syscall
+ * 1:			go to phase 2; no seccomp phase 2 needed
+ * anything else:	go to phase 2; pass return value to seccomp
+ */
+unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
+{
+	unsigned long ret = 0;
+	u32 work;
+
+	BUG_ON(regs != task_pt_regs(current));
+
+	work = ACCESS_ONCE(current_thread_info()->flags) &
+		_TIF_WORK_SYSCALL_ENTRY;
+
+	/*
+	 * If TIF_NOHZ is set, we are required to call user_exit() before
+	 * doing anything that could touch RCU.
+	 */
+	if (work & _TIF_NOHZ) {
+		user_exit();
+		work &= ~_TIF_NOHZ;
+	}
+
+#ifdef CONFIG_SECCOMP
+	/*
+	 * Do seccomp first -- it should minimize exposure of other
+	 * code, and keeping seccomp fast is probably more valuable
+	 * than the rest of this.
+	 */
+	if (work & _TIF_SECCOMP) {
+		struct seccomp_data sd;
+
+		sd.arch = arch;
+		sd.nr = regs->orig_ax;
+		sd.instruction_pointer = regs->ip;
+#ifdef CONFIG_X86_64
+		if (arch == AUDIT_ARCH_X86_64) {
+			sd.args[0] = regs->di;
+			sd.args[1] = regs->si;
+			sd.args[2] = regs->dx;
+			sd.args[3] = regs->r10;
+			sd.args[4] = regs->r8;
+			sd.args[5] = regs->r9;
+		} else
+#endif
+		{
+			sd.args[0] = regs->bx;
+			sd.args[1] = regs->cx;
+			sd.args[2] = regs->dx;
+			sd.args[3] = regs->si;
+			sd.args[4] = regs->di;
+			sd.args[5] = regs->bp;
+		}
+
+		BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
+		BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);
+
+		ret = seccomp_phase1(&sd);
+		if (ret == SECCOMP_PHASE1_SKIP) {
+			regs->orig_ax = -1;
+			ret = 0;
+		} else if (ret != SECCOMP_PHASE1_OK) {
+			return ret;  /* Go directly to phase 2 */
+		}
+
+		work &= ~_TIF_SECCOMP;
+	}
+#endif
+
+	/* Do our best to finish without phase 2. */
+	if (work == 0)
+		return ret;  /* seccomp and/or nohz only (ret == 0 here) */
+
+#ifdef CONFIG_AUDITSYSCALL
+	if (work == _TIF_SYSCALL_AUDIT) {
+		/*
+		 * If there is no more work to be done except auditing,
+		 * then audit in phase 1.  Phase 2 always audits, so, if
+		 * we audit here, then we can't go on to phase 2.
+		 */
+		do_audit_syscall_entry(regs, arch);
+		return 0;
+	}
+#endif
+
+	return 1;  /* Something is enabled that we can't handle in phase 1 */
+}
+
+/* Returns the syscall nr to run (which should match regs->orig_ax). */
+long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
+				unsigned long phase1_result)
+{
+	long ret = 0;
+	u32 work = ACCESS_ONCE(current_thread_info()->flags) &
+		_TIF_WORK_SYSCALL_ENTRY;
+
+	BUG_ON(regs != task_pt_regs(current));
+
+	/*
+	 * If we stepped into a sysenter/syscall insn, it trapped in
+	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+	 * If user-mode had set TF itself, then it's still clear from
+	 * do_debug() and we need to set it again to restore the user
+	 * state.  If we entered on the slow path, TF was already set.
+	 */
+	if (work & _TIF_SINGLESTEP)
+		regs->flags |= X86_EFLAGS_TF;
+
+#ifdef CONFIG_SECCOMP
+	/*
+	 * Call seccomp_phase2 before running the other hooks so that
+	 * they can see any changes made by a seccomp tracer.
+	 */
+	if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
+		/* seccomp failures shouldn't expose any additional code. */
+		return -1;
+	}
+#endif
+
+	if (unlikely(work & _TIF_SYSCALL_EMU))
+		ret = -1L;
+
+	if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
+	    tracehook_report_syscall_entry(regs))
+		ret = -1L;
+
+	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+		trace_sys_enter(regs, regs->orig_ax);
+
+	do_audit_syscall_entry(regs, arch);
+
+	return ret ?: regs->orig_ax;
+}
+
+long syscall_trace_enter(struct pt_regs *regs)
+{
+	u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
+	unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);
+
+	if (phase1_result == 0)
+		return regs->orig_ax;
+	else
+		return syscall_trace_enter_phase2(regs, arch, phase1_result);
+}
+
+void syscall_trace_leave(struct pt_regs *regs)
+{
+	bool step;
+
+	/*
+	 * We may come here right after calling schedule_user()
+	 * or do_notify_resume(), in which case we can be in RCU
+	 * user mode.
+	 */
+	user_exit();
+
+	audit_syscall_exit(regs);
+
+	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+		trace_sys_exit(regs, regs->ax);
+
+	/*
+	 * If TIF_SYSCALL_EMU is set, we only get here because of
+	 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
+	 * We already reported this syscall instruction in
+	 * syscall_trace_enter().
+	 */
+	step = unlikely(test_thread_flag(TIF_SINGLESTEP)) &&
+			!test_thread_flag(TIF_SYSCALL_EMU);
+	if (step || test_thread_flag(TIF_SYSCALL_TRACE))
+		tracehook_report_syscall_exit(regs, step);
+
+	user_enter();
+}
+
+/*
+ * notification of userspace execution resumption
+ * - triggered by the TIF_WORK_MASK flags
+ */
+__visible void
+do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
+{
+	user_exit();
+
+	if (thread_info_flags & _TIF_UPROBE)
+		uprobe_notify_resume(regs);
+
+	/* deal with pending signal delivery */
+	if (thread_info_flags & _TIF_SIGPENDING)
+		do_signal(regs);
+
+	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
+		clear_thread_flag(TIF_NOTIFY_RESUME);
+		tracehook_notify_resume(regs);
+	}
+	if (thread_info_flags & _TIF_USER_RETURN_NOTIFY)
+		fire_user_return_notifiers();
+
+	user_enter();
+}

arch/x86/include/asm/signal.h

@@ -30,6 +30,7 @@ typedef sigset_t compat_sigset_t;
 #endif /* __ASSEMBLY__ */
 #include <uapi/asm/signal.h>
 #ifndef __ASSEMBLY__
+extern void do_signal(struct pt_regs *regs);
 extern void do_notify_resume(struct pt_regs *, void *, __u32);
 
 #define __ARCH_HAS_SA_RESTORER