1 files changed, 288 insertions, 0 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
new file mode 100644
index 000000000..93a3122cd
--- /dev/null
+++ b/arch/x86/entry/common.c
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * common.c - C code for kernel entry and exit
+ * Copyright (c) 2015 Andrew Lutomirski
+ *
+ * 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/sched/task_stack.h>
+#include <linux/entry-common.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/errno.h>
+#include <linux/ptrace.h>
+#include <linux/export.h>
+#include <linux/nospec.h>
+#include <linux/syscalls.h>
+#include <linux/uaccess.h>
+
+#ifdef CONFIG_XEN_PV
+#include <xen/xen-ops.h>
+#include <xen/events.h>
+#endif
+
+#include <asm/desc.h>
+#include <asm/traps.h>
+#include <asm/vdso.h>
+#include <asm/cpufeature.h>
+#include <asm/fpu/api.h>
+#include <asm/nospec-branch.h>
+#include <asm/io_bitmap.h>
+#include <asm/syscall.h>
+#include <asm/irq_stack.h>
+
+#ifdef CONFIG_X86_64
+__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
+{
+	nr = syscall_enter_from_user_mode(regs, nr);
+
+	instrumentation_begin();
+	if (likely(nr < NR_syscalls)) {
+		nr = array_index_nospec(nr, NR_syscalls);
+		regs->ax = sys_call_table[nr](regs);
+#ifdef CONFIG_X86_X32_ABI
+	} else if (likely((nr & __X32_SYSCALL_BIT) &&
+			  (nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
+		nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
+					X32_NR_syscalls);
+		regs->ax = x32_sys_call_table[nr](regs);
+#endif
+	}
+	instrumentation_end();
+	syscall_exit_to_user_mode(regs);
+}
+#endif
+
+#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+static __always_inline unsigned int syscall_32_enter(struct pt_regs *regs)
+{
+	if (IS_ENABLED(CONFIG_IA32_EMULATION))
+		current_thread_info()->status |= TS_COMPAT;
+
+	return (unsigned int)regs->orig_ax;
+}
+
+/*
+ * Invoke a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.
+ */
+static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs,
+						  unsigned int nr)
+{
+	if (likely(nr < IA32_NR_syscalls)) {
+		nr = array_index_nospec(nr, IA32_NR_syscalls);
+		regs->ax = ia32_sys_call_table[nr](regs);
+	}
+}
+
+/* Handles int $0x80 */
+__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
+{
+	unsigned int nr = syscall_32_enter(regs);
+
+	/*
+	 * Subtlety here: if ptrace pokes something larger than 2^32-1 into
+	 * orig_ax, the unsigned int return value truncates it.  This may
+	 * or may not be necessary, but it matches the old asm behavior.
+	 */
+	nr = (unsigned int)syscall_enter_from_user_mode(regs, nr);
+	instrumentation_begin();
+
+	do_syscall_32_irqs_on(regs, nr);
+
+	instrumentation_end();
+	syscall_exit_to_user_mode(regs);
+}
+
+static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
+{
+	unsigned int nr = syscall_32_enter(regs);
+	int res;
+
+	/*
+	 * This cannot use syscall_enter_from_user_mode() as it has to
+	 * fetch EBP before invoking any of the syscall entry work
+	 * functions.
+	 */
+	syscall_enter_from_user_mode_prepare(regs);
+
+	instrumentation_begin();
+	/* Fetch EBP from where the vDSO stashed it. */
+	if (IS_ENABLED(CONFIG_X86_64)) {
+		/*
+		 * Micro-optimization: the pointer we're following is
+		 * explicitly 32 bits, so it can't be out of range.
+		 */
+		res = __get_user(*(u32 *)&regs->bp,
+			 (u32 __user __force *)(unsigned long)(u32)regs->sp);
+	} else {
+		res = get_user(*(u32 *)&regs->bp,
+		       (u32 __user __force *)(unsigned long)(u32)regs->sp);
+	}
+
+	if (res) {
+		/* User code screwed up. */
+		regs->ax = -EFAULT;
+
+		local_irq_disable();
+		instrumentation_end();
+		irqentry_exit_to_user_mode(regs);
+		return false;
+	}
+
+	/* The case truncates any ptrace induced syscall nr > 2^32 -1 */
+	nr = (unsigned int)syscall_enter_from_user_mode_work(regs, nr);
+
+	/* Now this is just like a normal syscall. */
+	do_syscall_32_irqs_on(regs, nr);
+
+	instrumentation_end();
+	syscall_exit_to_user_mode(regs);
+	return true;
+}
+
+/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
+__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
+{
+	/*
+	 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
+	 * convention.  Adjust regs so it looks like we entered using int80.
+	 */
+	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
+					vdso_image_32.sym_int80_landing_pad;
+
+	/*
+	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
+	 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
+	 * Fix it up.
+	 */
+	regs->ip = landing_pad;
+
+	/* Invoke the syscall. If it failed, keep it simple: use IRET. */
+	if (!__do_fast_syscall_32(regs))
+		return 0;
+
+#ifdef CONFIG_X86_64
+	/*
+	 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
+	 * SYSRETL is available on all 64-bit CPUs, so we don't need to
+	 * bother with SYSEXIT.
+	 *
+	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
+	 * because the ECX fixup above will ensure that this is essentially
+	 * never the case.
+	 */
+	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
+		regs->ip == landing_pad &&
+		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
+#else
+	/*
+	 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
+	 *
+	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
+	 * because the ECX fixup above will ensure that this is essentially
+	 * never the case.
+	 *
+	 * We don't allow syscalls at all from VM86 mode, but we still
+	 * need to check VM, because we might be returning from sys_vm86.
+	 */
+	return static_cpu_has(X86_FEATURE_SEP) &&
+		regs->cs == __USER_CS && regs->ss == __USER_DS &&
+		regs->ip == landing_pad &&
+		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
+#endif
+}
+
+/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
+__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
+{
+	/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
+	regs->sp = regs->bp;
+
+	/* SYSENTER clobbers EFLAGS.IF.  Assume it was set in usermode. */
+	regs->flags |= X86_EFLAGS_IF;
+
+	return do_fast_syscall_32(regs);
+}
+#endif
+
+SYSCALL_DEFINE0(ni_syscall)
+{
+	return -ENOSYS;
+}
+
+#ifdef CONFIG_XEN_PV
+#ifndef CONFIG_PREEMPTION
+/*
+ * Some hypercalls issued by the toolstack can take many 10s of
+ * seconds. Allow tasks running hypercalls via the privcmd driver to
+ * be voluntarily preempted even if full kernel preemption is
+ * disabled.
+ *
+ * Such preemptible hypercalls are bracketed by
+ * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
+ * calls.
+ */
+DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
+EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
+
+/*
+ * In case of scheduling the flag must be cleared and restored after
+ * returning from schedule as the task might move to a different CPU.
+ */
+static __always_inline bool get_and_clear_inhcall(void)
+{
+	bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);
+
+	__this_cpu_write(xen_in_preemptible_hcall, false);
+	return inhcall;
+}
+
+static __always_inline void restore_inhcall(bool inhcall)
+{
+	__this_cpu_write(xen_in_preemptible_hcall, inhcall);
+}
+#else
+static __always_inline bool get_and_clear_inhcall(void) { return false; }
+static __always_inline void restore_inhcall(bool inhcall) { }
+#endif
+
+static void __xen_pv_evtchn_do_upcall(void)
+{
+	irq_enter_rcu();
+	inc_irq_stat(irq_hv_callback_count);
+
+	xen_hvm_evtchn_do_upcall();
+
+	irq_exit_rcu();
+}
+
+__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs;
+	bool inhcall;
+	irqentry_state_t state;
+
+	state = irqentry_enter(regs);
+	old_regs = set_irq_regs(regs);
+
+	instrumentation_begin();
+	run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
+	instrumentation_end();
+
+	set_irq_regs(old_regs);
+
+	inhcall = get_and_clear_inhcall();
+	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
+		instrumentation_begin();
+		irqentry_exit_cond_resched();
+		instrumentation_end();
+		restore_inhcall(inhcall);
+	} else {
+		irqentry_exit(regs, state);
+	}
+}
+#endif /* CONFIG_XEN_PV */