319 lines
8.1 KiB
C
319 lines
8.1 KiB
C
/*
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* common.c - C code for kernel entry and exit
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* Copyright (c) 2015 Andrew Lutomirski
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* GPL v2
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*
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* Based on asm and ptrace code by many authors. The code here originated
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* in ptrace.c and signal.c.
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*/
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/smp.h>
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#include <linux/errno.h>
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#include <linux/ptrace.h>
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#include <linux/tracehook.h>
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#include <linux/audit.h>
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#include <linux/seccomp.h>
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#include <linux/signal.h>
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#include <linux/export.h>
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#include <linux/context_tracking.h>
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#include <linux/user-return-notifier.h>
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#include <linux/uprobes.h>
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#include <asm/desc.h>
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#include <asm/traps.h>
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#define CREATE_TRACE_POINTS
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#include <trace/events/syscalls.h>
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#ifdef CONFIG_CONTEXT_TRACKING
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/* Called on entry from user mode with IRQs off. */
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__visible void enter_from_user_mode(void)
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{
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CT_WARN_ON(ct_state() != CONTEXT_USER);
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user_exit();
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}
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#endif
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static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
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{
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#ifdef CONFIG_X86_64
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if (arch == AUDIT_ARCH_X86_64) {
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audit_syscall_entry(regs->orig_ax, regs->di,
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regs->si, regs->dx, regs->r10);
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} else
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#endif
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{
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audit_syscall_entry(regs->orig_ax, regs->bx,
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regs->cx, regs->dx, regs->si);
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}
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}
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/*
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* We can return 0 to resume the syscall or anything else to go to phase
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* 2. If we resume the syscall, we need to put something appropriate in
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* regs->orig_ax.
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*
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* NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
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* are fully functional.
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*
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* For phase 2's benefit, our return value is:
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* 0: resume the syscall
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* 1: go to phase 2; no seccomp phase 2 needed
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* anything else: go to phase 2; pass return value to seccomp
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*/
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unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
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{
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unsigned long ret = 0;
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u32 work;
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BUG_ON(regs != task_pt_regs(current));
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work = ACCESS_ONCE(current_thread_info()->flags) &
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_TIF_WORK_SYSCALL_ENTRY;
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#ifdef CONFIG_CONTEXT_TRACKING
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/*
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* If TIF_NOHZ is set, we are required to call user_exit() before
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* doing anything that could touch RCU.
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*/
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if (work & _TIF_NOHZ) {
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enter_from_user_mode();
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work &= ~_TIF_NOHZ;
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}
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#endif
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#ifdef CONFIG_SECCOMP
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/*
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* Do seccomp first -- it should minimize exposure of other
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* code, and keeping seccomp fast is probably more valuable
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* than the rest of this.
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*/
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if (work & _TIF_SECCOMP) {
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struct seccomp_data sd;
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sd.arch = arch;
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sd.nr = regs->orig_ax;
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sd.instruction_pointer = regs->ip;
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#ifdef CONFIG_X86_64
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if (arch == AUDIT_ARCH_X86_64) {
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sd.args[0] = regs->di;
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sd.args[1] = regs->si;
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sd.args[2] = regs->dx;
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sd.args[3] = regs->r10;
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sd.args[4] = regs->r8;
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sd.args[5] = regs->r9;
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} else
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#endif
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{
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sd.args[0] = regs->bx;
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sd.args[1] = regs->cx;
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sd.args[2] = regs->dx;
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sd.args[3] = regs->si;
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sd.args[4] = regs->di;
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sd.args[5] = regs->bp;
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}
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BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
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BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);
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ret = seccomp_phase1(&sd);
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if (ret == SECCOMP_PHASE1_SKIP) {
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regs->orig_ax = -1;
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ret = 0;
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} else if (ret != SECCOMP_PHASE1_OK) {
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return ret; /* Go directly to phase 2 */
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}
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work &= ~_TIF_SECCOMP;
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}
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#endif
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/* Do our best to finish without phase 2. */
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if (work == 0)
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return ret; /* seccomp and/or nohz only (ret == 0 here) */
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#ifdef CONFIG_AUDITSYSCALL
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if (work == _TIF_SYSCALL_AUDIT) {
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/*
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* If there is no more work to be done except auditing,
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* then audit in phase 1. Phase 2 always audits, so, if
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* we audit here, then we can't go on to phase 2.
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*/
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do_audit_syscall_entry(regs, arch);
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return 0;
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}
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#endif
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return 1; /* Something is enabled that we can't handle in phase 1 */
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}
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/* Returns the syscall nr to run (which should match regs->orig_ax). */
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long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
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unsigned long phase1_result)
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{
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long ret = 0;
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u32 work = ACCESS_ONCE(current_thread_info()->flags) &
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_TIF_WORK_SYSCALL_ENTRY;
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BUG_ON(regs != task_pt_regs(current));
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/*
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* If we stepped into a sysenter/syscall insn, it trapped in
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* kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
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* If user-mode had set TF itself, then it's still clear from
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* do_debug() and we need to set it again to restore the user
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* state. If we entered on the slow path, TF was already set.
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*/
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if (work & _TIF_SINGLESTEP)
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regs->flags |= X86_EFLAGS_TF;
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#ifdef CONFIG_SECCOMP
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/*
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* Call seccomp_phase2 before running the other hooks so that
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* they can see any changes made by a seccomp tracer.
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*/
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if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
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/* seccomp failures shouldn't expose any additional code. */
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return -1;
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}
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#endif
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if (unlikely(work & _TIF_SYSCALL_EMU))
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ret = -1L;
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if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
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tracehook_report_syscall_entry(regs))
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ret = -1L;
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if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
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trace_sys_enter(regs, regs->orig_ax);
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do_audit_syscall_entry(regs, arch);
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return ret ?: regs->orig_ax;
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}
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long syscall_trace_enter(struct pt_regs *regs)
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{
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u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
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unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);
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if (phase1_result == 0)
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return regs->orig_ax;
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else
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return syscall_trace_enter_phase2(regs, arch, phase1_result);
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}
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static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
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{
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unsigned long top_of_stack =
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(unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
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return (struct thread_info *)(top_of_stack - THREAD_SIZE);
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}
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/* Called with IRQs disabled. */
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__visible void prepare_exit_to_usermode(struct pt_regs *regs)
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{
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if (WARN_ON(!irqs_disabled()))
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local_irq_disable();
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/*
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* In order to return to user mode, we need to have IRQs off with
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* none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
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* _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags
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* can be set at any time on preemptable kernels if we have IRQs on,
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* so we need to loop. Disabling preemption wouldn't help: doing the
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* work to clear some of the flags can sleep.
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*/
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while (true) {
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u32 cached_flags =
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READ_ONCE(pt_regs_to_thread_info(regs)->flags);
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if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME |
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_TIF_UPROBE | _TIF_NEED_RESCHED |
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_TIF_USER_RETURN_NOTIFY)))
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break;
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/* We have work to do. */
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local_irq_enable();
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if (cached_flags & _TIF_NEED_RESCHED)
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schedule();
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if (cached_flags & _TIF_UPROBE)
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uprobe_notify_resume(regs);
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/* deal with pending signal delivery */
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if (cached_flags & _TIF_SIGPENDING)
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do_signal(regs);
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if (cached_flags & _TIF_NOTIFY_RESUME) {
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clear_thread_flag(TIF_NOTIFY_RESUME);
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tracehook_notify_resume(regs);
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}
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if (cached_flags & _TIF_USER_RETURN_NOTIFY)
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fire_user_return_notifiers();
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/* Disable IRQs and retry */
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local_irq_disable();
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}
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user_enter();
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}
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/*
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* Called with IRQs on and fully valid regs. Returns with IRQs off in a
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* state such that we can immediately switch to user mode.
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*/
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__visible void syscall_return_slowpath(struct pt_regs *regs)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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u32 cached_flags = READ_ONCE(ti->flags);
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bool step;
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CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
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if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled",
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regs->orig_ax))
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local_irq_enable();
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/*
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* First do one-time work. If these work items are enabled, we
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* want to run them exactly once per syscall exit with IRQs on.
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*/
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if (cached_flags & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |
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_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)) {
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audit_syscall_exit(regs);
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if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
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trace_sys_exit(regs, regs->ax);
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/*
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* If TIF_SYSCALL_EMU is set, we only get here because of
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* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
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* We already reported this syscall instruction in
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* syscall_trace_enter().
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*/
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step = unlikely(
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(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
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== _TIF_SINGLESTEP);
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if (step || cached_flags & _TIF_SYSCALL_TRACE)
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tracehook_report_syscall_exit(regs, step);
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}
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#ifdef CONFIG_COMPAT
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/*
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* Compat syscalls set TS_COMPAT. Make sure we clear it before
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* returning to user mode.
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*/
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ti->status &= ~TS_COMPAT;
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#endif
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local_irq_disable();
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prepare_exit_to_usermode(regs);
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}
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