[patch V2 10/17] entry: Provide generic syscall entry functionality

[Thomas Gleixner]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

On syscall entry certain work needs to be done conditionally like tracing,
seccomp etc. This code is duplicated in all architectures.

Provide a generic version.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
V2: Fix function documentation (Mike)
    Add comment about return value (Andy)
---
 arch/Kconfig                 |    3 
 include/linux/entry-common.h |  132 +++++++++++++++++++++++++++++++++++++++++++
 kernel/Makefile              |    1 
 kernel/entry/Makefile        |    3 
 kernel/entry/common.c        |   33 ++++++++++
 5 files changed, 172 insertions(+)

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -27,6 +27,9 @@ config HAVE_IMA_KEXEC
 config HOTPLUG_SMT
 	bool
 
+config GENERIC_ENTRY
+       bool
+
 config OPROFILE
 	tristate "OProfile system profiling"
 	depends on PROFILING
--- /dev/null
+++ b/include/linux/entry-common.h
@@ -0,0 +1,132 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_ENTRYCOMMON_H
+#define __LINUX_ENTRYCOMMON_H
+
+#include <linux/tracehook.h>
+#include <linux/syscalls.h>
+#include <linux/seccomp.h>
+#include <linux/sched.h>
+#include <linux/audit.h>
+
+#include <asm/entry-common.h>
+
+/*
+ * Define dummy _TIF work flags if not defined by the architecture or for
+ * disabled functionality.
+ */
+#ifndef _TIF_SYSCALL_TRACE
+# define _TIF_SYSCALL_TRACE		(0)
+#endif
+
+#ifndef _TIF_SYSCALL_EMU
+# define _TIF_SYSCALL_EMU		(0)
+#endif
+
+#ifndef _TIF_SYSCALL_TRACEPOINT
+# define _TIF_SYSCALL_TRACEPOINT	(0)
+#endif
+
+#ifndef _TIF_SECCOMP
+# define _TIF_SECCOMP			(0)
+#endif
+
+#ifndef _TIF_AUDIT
+# define _TIF_AUDIT			(0)
+#endif
+
+/*
+ * TIF flags handled in syscall_enter_from_usermode()
+ */
+#ifndef ARCH_SYSCALL_ENTER_WORK
+# define ARCH_SYSCALL_ENTER_WORK	(0)
+#endif
+
+#define SYSCALL_ENTER_WORK						\
+	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | TIF_SECCOMP |	\
+	 _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU |			\
+	 ARCH_SYSCALL_ENTER_WORK)
+
+/**
+ * arch_syscall_enter_tracehook - Wrapper around tracehook_report_syscall_entry()
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Returns: 0 on success or an error code to skip the syscall.
+ *
+ * Defaults to tracehook_report_syscall_entry(). Can be replaced by
+ * architecture specific code.
+ *
+ * Invoked from syscall_enter_from_usermode()
+ */
+static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs);
+
+#ifndef arch_syscall_enter_tracehook
+static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs)
+{
+	return tracehook_report_syscall_entry(regs);
+}
+#endif
+
+/**
+ * arch_syscall_enter_seccomp - Architecture specific seccomp invocation
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Returns: The original or a modified syscall number
+ *
+ * Invoked from syscall_enter_from_usermode(). Can be replaced by
+ * architecture specific code.
+ */
+static inline long arch_syscall_enter_seccomp(struct pt_regs *regs);
+
+#ifndef arch_syscall_enter_seccomp
+static inline long arch_syscall_enter_seccomp(struct pt_regs *regs)
+{
+	return secure_computing(NULL);
+}
+#endif
+
+/**
+ * arch_syscall_enter_audit - Architecture specific audit invocation
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Invoked from syscall_enter_from_usermode(). Must be replaced by
+ * architecture specific code if the architecture supports audit.
+ */
+static inline void arch_syscall_enter_audit(struct pt_regs *regs);
+
+#ifndef arch_syscall_enter_audit
+static inline void arch_syscall_enter_audit(struct pt_regs *regs) { }
+#endif
+
+/* Common syscall enter function */
+long core_syscall_enter_from_usermode(struct pt_regs *regs, long syscall);
+
+/**
+ * syscall_enter_from_usermode - Check and handle work before invoking
+ *				 a syscall
+ * @regs:	Pointer to currents pt_regs
+ * @syscall:	The syscall number
+ *
+ * Invoked from architecture specific syscall entry code with interrupts
+ * enabled.
+ *
+ * Returns: The original or a modified syscall number
+ *
+ * If the returned syscall number is -1 then the syscall should be
+ * skipped. In this case the caller may invoke syscall_set_error() or
+ * syscall_set_return_value() first.  If neither of those is called and -1
+ * is returned, then the syscall will fail with ENOSYS.
+ */
+static inline long syscall_enter_from_usermode(struct pt_regs *regs,
+					       long syscall)
+{
+	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+
+	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
+		BUG_ON(regs != task_pt_regs(current));
+
+	if (ti_work & SYSCALL_ENTER_WORK)
+		syscall = core_syscall_enter_from_usermode(regs, syscall);
+	return syscall;
+}
+
+#endif
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -43,6 +43,7 @@ obj-y += irq/
 obj-y += rcu/
 obj-y += livepatch/
 obj-y += dma/
+obj-y += entry/
 
 obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
--- /dev/null
+++ b/kernel/entry/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_GENERIC_ENTRY) += common.o
--- /dev/null
+++ b/kernel/entry/common.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/context_tracking.h>
+#include <linux/entry-common.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
+long core_syscall_enter_from_usermode(struct pt_regs *regs, long syscall)
+{
+	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+	unsigned long ret = 0;
+
+	if (ti_work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) {
+		ret = arch_syscall_enter_tracehook(regs);
+		if (ret || (ti_work & _TIF_SYSCALL_EMU))
+			return -1L;
+	}
+
+	/* Do seccomp after ptrace, to catch any tracer changes. */
+	if (ti_work & _TIF_SECCOMP) {
+		ret = arch_syscall_enter_seccomp(regs);
+		if (ret == -1L)
+			return ret;
+	}
+
+	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+		trace_sys_enter(regs, syscall);
+
+	arch_syscall_enter_audit(regs);
+
+	return ret ? : syscall;
+}