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authorThomas Gleixner <tglx@linutronix.de>2020-07-22 23:59:57 +0200
committerThomas Gleixner <tglx@linutronix.de>2020-07-24 14:59:03 +0200
commita9f3a74a29af095f3e1b89e9176f8127912ae0f0 (patch)
treeb21efe2125aaf7d3ff9c336927be6e0abd26628e /kernel/entry
parent142781e108b13b2b0e8f035cfb5bfbbc8f14d887 (diff)
downloadlinux-a9f3a74a29af095f3e1b89e9176f8127912ae0f0.tar.bz2
entry: Provide generic syscall exit function
Like syscall entry all architectures have similar and pointlessly different code to handle pending work before returning from a syscall to user space. 1) One-time syscall exit work: - rseq syscall exit - audit - syscall tracing - tracehook (single stepping) 2) Preparatory work - Exit to user mode loop (common TIF handling). - Architecture specific one time work arch_exit_to_user_mode_prepare() - Address limit and lockdep checks 3) Final transition (lockdep, tracing, context tracking, RCU). Invokes arch_exit_to_user_mode() to handle e.g. speculation mitigations Provide a generic version based on the x86 code which has all the RCU and instrumentation protections right. Provide a variant for interrupt return to user mode as well which shares the above #2 and #3 work items. After syscall_exit_to_user_mode() and irqentry_exit_to_user_mode() the architecture code just has to return to user space. The code after returning from these functions must not be instrumented. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lkml.kernel.org/r/20200722220519.613977173@linutronix.de
Diffstat (limited to 'kernel/entry')
-rw-r--r--kernel/entry/common.c169
1 files changed, 169 insertions, 0 deletions
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 1d636dee2fec..0a051bb91a56 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -2,6 +2,8 @@
#include <linux/context_tracking.h>
#include <linux/entry-common.h>
+#include <linux/livepatch.h>
+#include <linux/audit.h>
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
@@ -82,7 +84,174 @@ noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
return syscall;
}
+/**
+ * exit_to_user_mode - Fixup state when exiting to user mode
+ *
+ * Syscall/interupt exit enables interrupts, but the kernel state is
+ * interrupts disabled when this is invoked. Also tell RCU about it.
+ *
+ * 1) Trace interrupts on state
+ * 2) Invoke context tracking if enabled to adjust RCU state
+ * 3) Invoke architecture specific last minute exit code, e.g. speculation
+ * mitigations, etc.
+ * 4) Tell lockdep that interrupts are enabled
+ */
+static __always_inline void exit_to_user_mode(void)
+{
+ instrumentation_begin();
+ trace_hardirqs_on_prepare();
+ lockdep_hardirqs_on_prepare(CALLER_ADDR0);
+ instrumentation_end();
+
+ user_enter_irqoff();
+ arch_exit_to_user_mode();
+ lockdep_hardirqs_on(CALLER_ADDR0);
+}
+
+/* Workaround to allow gradual conversion of architecture code */
+void __weak arch_do_signal(struct pt_regs *regs) { }
+
+static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
+ unsigned long ti_work)
+{
+ /*
+ * Before returning to user space ensure that all pending work
+ * items have been completed.
+ */
+ while (ti_work & EXIT_TO_USER_MODE_WORK) {
+
+ local_irq_enable_exit_to_user(ti_work);
+
+ if (ti_work & _TIF_NEED_RESCHED)
+ schedule();
+
+ if (ti_work & _TIF_UPROBE)
+ uprobe_notify_resume(regs);
+
+ if (ti_work & _TIF_PATCH_PENDING)
+ klp_update_patch_state(current);
+
+ if (ti_work & _TIF_SIGPENDING)
+ arch_do_signal(regs);
+
+ if (ti_work & _TIF_NOTIFY_RESUME) {
+ clear_thread_flag(TIF_NOTIFY_RESUME);
+ tracehook_notify_resume(regs);
+ rseq_handle_notify_resume(NULL, regs);
+ }
+
+ /* Architecture specific TIF work */
+ arch_exit_to_user_mode_work(regs, ti_work);
+
+ /*
+ * Disable interrupts and reevaluate the work flags as they
+ * might have changed while interrupts and preemption was
+ * enabled above.
+ */
+ local_irq_disable_exit_to_user();
+ ti_work = READ_ONCE(current_thread_info()->flags);
+ }
+
+ /* Return the latest work state for arch_exit_to_user_mode() */
+ return ti_work;
+}
+
+static void exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+ unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+
+ lockdep_assert_irqs_disabled();
+
+ if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
+ ti_work = exit_to_user_mode_loop(regs, ti_work);
+
+ arch_exit_to_user_mode_prepare(regs, ti_work);
+
+ /* Ensure that the address limit is intact and no locks are held */
+ addr_limit_user_check();
+ lockdep_assert_irqs_disabled();
+ lockdep_sys_exit();
+}
+
+#ifndef _TIF_SINGLESTEP
+static inline bool report_single_step(unsigned long ti_work)
+{
+ return false;
+}
+#else
+/*
+ * If TIF_SYSCALL_EMU is set, then the only reason to report is when
+ * TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
+ * instruction has been already reported in syscall_enter_from_usermode().
+ */
+#define SYSEMU_STEP (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)
+
+static inline bool report_single_step(unsigned long ti_work)
+{
+ return (ti_work & SYSEMU_STEP) == _TIF_SINGLESTEP;
+}
+#endif
+
+static void syscall_exit_work(struct pt_regs *regs, unsigned long ti_work)
+{
+ bool step;
+
+ audit_syscall_exit(regs);
+
+ if (ti_work & _TIF_SYSCALL_TRACEPOINT)
+ trace_sys_exit(regs, syscall_get_return_value(current, regs));
+
+ step = report_single_step(ti_work);
+ if (step || ti_work & _TIF_SYSCALL_TRACE)
+ arch_syscall_exit_tracehook(regs, step);
+}
+
+/*
+ * Syscall specific exit to user mode preparation. Runs with interrupts
+ * enabled.
+ */
+static void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+ u32 cached_flags = READ_ONCE(current_thread_info()->flags);
+ unsigned long nr = syscall_get_nr(current, regs);
+
+ CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+
+ if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
+ if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr))
+ local_irq_enable();
+ }
+
+ rseq_syscall(regs);
+
+ /*
+ * Do one-time syscall specific work. If these work items are
+ * enabled, we want to run them exactly once per syscall exit with
+ * interrupts enabled.
+ */
+ if (unlikely(cached_flags & SYSCALL_EXIT_WORK))
+ syscall_exit_work(regs, cached_flags);
+}
+
+__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
+{
+ instrumentation_begin();
+ syscall_exit_to_user_mode_prepare(regs);
+ local_irq_disable_exit_to_user();
+ exit_to_user_mode_prepare(regs);
+ instrumentation_end();
+ exit_to_user_mode();
+}
+
noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
{
enter_from_user_mode(regs);
}
+
+noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
+{
+ instrumentation_begin();
+ exit_to_user_mode_prepare(regs);
+ instrumentation_end();
+ exit_to_user_mode();
+}