lguest: add operations to get/set a register from the Launcher.

We use the ptrace API struct, and we currently don't let them set
anything but the normal registers (we'd have to filter the others).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/lguest/core.c

@@ -208,6 +208,14 @@ void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
  */
 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 {
+	/* If the launcher asked for a register with LHREQ_GETREG */
+	if (cpu->reg_read) {
+		if (put_user(*cpu->reg_read, user))
+			return -EFAULT;
+		cpu->reg_read = NULL;
+		return sizeof(*cpu->reg_read);
+	}
+
 	/* We stop running once the Guest is dead. */
 	while (!cpu->lg->dead) {
 		unsigned int irq;

drivers/lguest/lg.h

@@ -52,6 +52,8 @@ struct lg_cpu {
 
 	unsigned long pending_notify; /* pfn from LHCALL_NOTIFY */
 
+	unsigned long *reg_read; /* register from LHREQ_GETREG */
+
 	/* At end of a page shared mapped over lguest_pages in guest. */
 	unsigned long regs_page;
 	struct lguest_regs *regs;
@@ -210,6 +212,7 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu);
 int lguest_arch_init_hypercalls(struct lg_cpu *cpu);
 int lguest_arch_do_hcall(struct lg_cpu *cpu, struct hcall_args *args);
 void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start);
+unsigned long *lguest_arch_regptr(struct lg_cpu *cpu, size_t reg_off, bool any);
 
 /* <arch>/switcher.S: */
 extern char start_switcher_text[], end_switcher_text[], switch_to_guest[];

drivers/lguest/lguest_user.c

@@ -173,6 +173,51 @@ static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
 	return err;
 }
 
+/* The Launcher can get the registers, and also set some of them. */
+static int getreg_setup(struct lg_cpu *cpu, const unsigned long __user *input)
+{
+	unsigned long which;
+
+	/* We re-use the ptrace structure to specify which register to read. */
+	if (get_user(which, input) != 0)
+		return -EFAULT;
+
+	/*
+	 * We set up the cpu register pointer, and their next read will
+	 * actually get the value (instead of running the guest).
+	 *
+	 * The last argument 'true' says we can access any register.
+	 */
+	cpu->reg_read = lguest_arch_regptr(cpu, which, true);
+	if (!cpu->reg_read)
+		return -ENOENT;
+
+	/* And because this is a write() call, we return the length used. */
+	return sizeof(unsigned long) * 2;
+}
+
+static int setreg(struct lg_cpu *cpu, const unsigned long __user *input)
+{
+	unsigned long which, value, *reg;
+
+	/* We re-use the ptrace structure to specify which register to read. */
+	if (get_user(which, input) != 0)
+		return -EFAULT;
+	input++;
+	if (get_user(value, input) != 0)
+		return -EFAULT;
+
+	/* The last argument 'false' means we can't access all registers. */
+	reg = lguest_arch_regptr(cpu, which, false);
+	if (!reg)
+		return -ENOENT;
+
+	*reg = value;
+
+	/* And because this is a write() call, we return the length used. */
+	return sizeof(unsigned long) * 3;
+}
+
 /*L:050
  * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
  * number to /dev/lguest.
@@ -434,6 +479,10 @@ static ssize_t write(struct file *file, const char __user *in,
 		return user_send_irq(cpu, input);
 	case LHREQ_EVENTFD:
 		return attach_eventfd(lg, input);
+	case LHREQ_GETREG:
+		return getreg_setup(cpu, input);
+	case LHREQ_SETREG:
+		return setreg(cpu, input);
 	default:
 		return -EINVAL;
 	}

drivers/lguest/x86/core.c

@@ -181,6 +181,52 @@ static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages)
 }
 /*:*/
 
+unsigned long *lguest_arch_regptr(struct lg_cpu *cpu, size_t reg_off, bool any)
+{
+	switch (reg_off) {
+	case offsetof(struct pt_regs, bx):
+		return &cpu->regs->ebx;
+	case offsetof(struct pt_regs, cx):
+		return &cpu->regs->ecx;
+	case offsetof(struct pt_regs, dx):
+		return &cpu->regs->edx;
+	case offsetof(struct pt_regs, si):
+		return &cpu->regs->esi;
+	case offsetof(struct pt_regs, di):
+		return &cpu->regs->edi;
+	case offsetof(struct pt_regs, bp):
+		return &cpu->regs->ebp;
+	case offsetof(struct pt_regs, ax):
+		return &cpu->regs->eax;
+	case offsetof(struct pt_regs, ip):
+		return &cpu->regs->eip;
+	case offsetof(struct pt_regs, sp):
+		return &cpu->regs->esp;
+	}
+
+	/* Launcher can read these, but we don't allow any setting. */
+	if (any) {
+		switch (reg_off) {
+		case offsetof(struct pt_regs, ds):
+			return &cpu->regs->ds;
+		case offsetof(struct pt_regs, es):
+			return &cpu->regs->es;
+		case offsetof(struct pt_regs, fs):
+			return &cpu->regs->fs;
+		case offsetof(struct pt_regs, gs):
+			return &cpu->regs->gs;
+		case offsetof(struct pt_regs, cs):
+			return &cpu->regs->cs;
+		case offsetof(struct pt_regs, flags):
+			return &cpu->regs->eflags;
+		case offsetof(struct pt_regs, ss):
+			return &cpu->regs->ss;
+		}
+	}
+
+	return NULL;
+}
+
 /*M:002
  * There are hooks in the scheduler which we can register to tell when we
  * get kicked off the CPU (preempt_notifier_register()).  This would allow us

include/linux/lguest_launcher.h

@@ -63,6 +63,8 @@ enum lguest_req
 	LHREQ_IRQ, /* + irq */
 	LHREQ_BREAK, /* No longer used */
 	LHREQ_EVENTFD, /* + address, fd. */
+	LHREQ_GETREG, /* + offset within struct pt_regs (then read value). */
+	LHREQ_SETREG, /* + offset within struct pt_regs, value. */
 };
 
 /*