/*P:400 * This contains run_guest() which actually calls into the Host<->Guest * Switcher and analyzes the return, such as determining if the Guest wants the * Host to do something. This file also contains useful helper routines. :*/ #include <linux/module.h> #include <linux/stringify.h> #include <linux/stddef.h> #include <linux/io.h> #include <linux/mm.h> #include <linux/vmalloc.h> #include <linux/cpu.h> #include <linux/freezer.h> #include <linux/highmem.h> #include <linux/slab.h> #include <asm/paravirt.h> #include <asm/pgtable.h> #include <asm/uaccess.h> #include <asm/poll.h> #include <asm/asm-offsets.h> #include "lg.h" unsigned long switcher_addr; struct page **lg_switcher_pages; static struct vm_struct *switcher_vma; /* This One Big lock protects all inter-guest data structures. */ DEFINE_MUTEX(lguest_lock); /*H:010 * We need to set up the Switcher at a high virtual address. Remember the * Switcher is a few hundred bytes of assembler code which actually changes the * CPU to run the Guest, and then changes back to the Host when a trap or * interrupt happens. * * The Switcher code must be at the same virtual address in the Guest as the * Host since it will be running as the switchover occurs. * * Trying to map memory at a particular address is an unusual thing to do, so * it's not a simple one-liner. */ static __init int map_switcher(void) { int i, err; /* * Map the Switcher in to high memory. * * It turns out that if we choose the address 0xFFC00000 (4MB under the * top virtual address), it makes setting up the page tables really * easy. */ /* We assume Switcher text fits into a single page. */ if (end_switcher_text - start_switcher_text > PAGE_SIZE) { printk(KERN_ERR "lguest: switcher text too large (%zu)\n", end_switcher_text - start_switcher_text); return -EINVAL; } /* * We allocate an array of struct page pointers. map_vm_area() wants * this, rather than just an array of pages. */ lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0]) * TOTAL_SWITCHER_PAGES, GFP_KERNEL); if (!lg_switcher_pages) { err = -ENOMEM; goto out; } /* * Now we actually allocate the pages. The Guest will see these pages, * so we make sure they're zeroed. */ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) { lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO); if (!lg_switcher_pages[i]) { err = -ENOMEM; goto free_some_pages; } } /* * We place the Switcher underneath the fixmap area, which is the * highest virtual address we can get. This is important, since we * tell the Guest it can't access this memory, so we want its ceiling * as high as possible. */ switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE; /* * Now we reserve the "virtual memory area" we want. We might * not get it in theory, but in practice it's worked so far. * The end address needs +1 because __get_vm_area allocates an * extra guard page, so we need space for that. */ switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE, VM_ALLOC, switcher_addr, switcher_addr + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE); if (!switcher_vma) { err = -ENOMEM; printk("lguest: could not map switcher pages high\n"); goto free_pages; } /* * This code actually sets up the pages we've allocated to appear at * switcher_addr. map_vm_area() takes the vma we allocated above, the * kind of pages we're mapping (kernel pages), and a pointer to our * array of struct pages. */ err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages); if (err) { printk("lguest: map_vm_area failed: %i\n", err); goto free_vma; } /* * Now the Switcher is mapped at the right address, we can't fail! * Copy in the compiled-in Switcher code (from x86/switcher_32.S). */ memcpy(switcher_vma->addr, start_switcher_text, end_switcher_text - start_switcher_text); printk(KERN_INFO "lguest: mapped switcher at %p\n", switcher_vma->addr); /* And we succeeded... */ return 0; free_vma: vunmap(switcher_vma->addr); free_pages: i = TOTAL_SWITCHER_PAGES; free_some_pages: for (--i; i >= 0; i--) __free_pages(lg_switcher_pages[i], 0); kfree(lg_switcher_pages); out: return err; } /*:*/ /* Cleaning up the mapping when the module is unloaded is almost... too easy. */ static void unmap_switcher(void) { unsigned int i; /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */ vunmap(switcher_vma->addr); /* Now we just need to free the pages we copied the switcher into */ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) __free_pages(lg_switcher_pages[i], 0); kfree(lg_switcher_pages); } /*H:032 * Dealing With Guest Memory. * * Before we go too much further into the Host, we need to grok the routines * we use to deal with Guest memory. * * When the Guest gives us (what it thinks is) a physical address, we can use * the normal copy_from_user() & copy_to_user() on the corresponding place in * the memory region allocated by the Launcher. * * But we can't trust the Guest: it might be trying to access the Launcher * code. We have to check that the range is below the pfn_limit the Launcher * gave us. We have to make sure that addr + len doesn't give us a false * positive by overflowing, too. */ bool lguest_address_ok(const struct lguest *lg, unsigned long addr, unsigned long len) { return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr); } /* * This routine copies memory from the Guest. Here we can see how useful the * kill_lguest() routine we met in the Launcher can be: we return a random * value (all zeroes) instead of needing to return an error. */ void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes) { if (!lguest_address_ok(cpu->lg, addr, bytes) || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) { /* copy_from_user should do this, but as we rely on it... */ memset(b, 0, bytes); kill_guest(cpu, "bad read address %#lx len %u", addr, bytes); } } /* This is the write (copy into Guest) version. */ void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b, unsigned bytes) { if (!lguest_address_ok(cpu->lg, addr, bytes) || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0) kill_guest(cpu, "bad write address %#lx len %u", addr, bytes); } /*:*/ /*H:030 * Let's jump straight to the the main loop which runs the Guest. * Remember, this is called by the Launcher reading /dev/lguest, and we keep * going around and around until something interesting happens. */ 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; bool more; /* First we run any hypercalls the Guest wants done. */ if (cpu->hcall) do_hypercalls(cpu); /* Do we have to tell the Launcher about a trap? */ if (cpu->pending.trap) { if (copy_to_user(user, &cpu->pending, sizeof(cpu->pending))) return -EFAULT; return sizeof(cpu->pending); } /* * All long-lived kernel loops need to check with this horrible * thing called the freezer. If the Host is trying to suspend, * it stops us. */ try_to_freeze(); /* Check for signals */ if (signal_pending(current)) return -ERESTARTSYS; /* * Check if there are any interrupts which can be delivered now: * if so, this sets up the hander to be executed when we next * run the Guest. */ irq = interrupt_pending(cpu, &more); if (irq < LGUEST_IRQS) try_deliver_interrupt(cpu, irq, more); /* * Just make absolutely sure the Guest is still alive. One of * those hypercalls could have been fatal, for example. */ if (cpu->lg->dead) break; /* * If the Guest asked to be stopped, we sleep. The Guest's * clock timer will wake us. */ if (cpu->halted) { set_current_state(TASK_INTERRUPTIBLE); /* * Just before we sleep, make sure no interrupt snuck in * which we should be doing. */ if (interrupt_pending(cpu, &more) < LGUEST_IRQS) set_current_state(TASK_RUNNING); else schedule(); continue; } /* * OK, now we're ready to jump into the Guest. First we put up * the "Do Not Disturb" sign: */ local_irq_disable(); /* Actually run the Guest until something happens. */ lguest_arch_run_guest(cpu); /* Now we're ready to be interrupted or moved to other CPUs */ local_irq_enable(); /* Now we deal with whatever happened to the Guest. */ lguest_arch_handle_trap(cpu); } /* Special case: Guest is 'dead' but wants a reboot. */ if (cpu->lg->dead == ERR_PTR(-ERESTART)) return -ERESTART; /* The Guest is dead => "No such file or directory" */ return -ENOENT; } /*H:000 * Welcome to the Host! * * By this point your brain has been tickled by the Guest code and numbed by * the Launcher code; prepare for it to be stretched by the Host code. This is * the heart. Let's begin at the initialization routine for the Host's lg * module. */ static int __init init(void) { int err; /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */ if (get_kernel_rpl() != 0) { printk("lguest is afraid of being a guest\n"); return -EPERM; } /* First we put the Switcher up in very high virtual memory. */ err = map_switcher(); if (err) goto out; /* We might need to reserve an interrupt vector. */ err = init_interrupts(); if (err) goto unmap; /* /dev/lguest needs to be registered. */ err = lguest_device_init(); if (err) goto free_interrupts; /* Finally we do some architecture-specific setup. */ lguest_arch_host_init(); /* All good! */ return 0; free_interrupts: free_interrupts(); unmap: unmap_switcher(); out: return err; } /* Cleaning up is just the same code, backwards. With a little French. */ static void __exit fini(void) { lguest_device_remove(); free_interrupts(); unmap_switcher(); lguest_arch_host_fini(); } /*:*/ /* * The Host side of lguest can be a module. This is a nice way for people to * play with it. */ module_init(init); module_exit(fini); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");