lguest: documentation V: Host (bff672e6) · Commits · 戴 / test

drivers/lguest/core.c

+258 −15

Original line number	Diff line number	Diff line
		@@ -64,11 +64,33 @@ static struct lguest_pages *lguest_pages(unsigned int cpu)
		(SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
		}

		/*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. We also set up the per-cpu parts of the
		* Switcher here.
		*/
		static __init int map_switcher(void)
		{
		int i, err;
		struct page **pagep;

		/*
		* 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 allocate an array of "struct page"s. map_vm_area() wants the
		* pages in this form, rather than just an array of pointers. */
		switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
		GFP_KERNEL);
		if (!switcher_page) {
		@@ -76,6 +98,8 @@ static __init int map_switcher(void)
		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++) {
		unsigned long addr = get_zeroed_page(GFP_KERNEL);
		if (!addr) {
		@@ -85,6 +109,9 @@ static __init int map_switcher(void)
		switcher_page[i] = virt_to_page(addr);
		}

		/* Now we reserve the "virtual memory area" we want: 0xFFC00000
		* (SWITCHER_ADDR). We might not get it in theory, but in practice
		* it's worked so far. */
		switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
		VM_ALLOC, SWITCHER_ADDR, VMALLOC_END);
		if (!switcher_vma) {
		@@ -93,49 +120,105 @@ static __init int map_switcher(void)
		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. It increments that pointer, but we don't
		* care. */
		pagep = switcher_page;
		err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep);
		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 switcher.S). */
		memcpy(switcher_vma->addr, start_switcher_text,
		end_switcher_text - start_switcher_text);

		/* Fix up IDT entries to point into copied text. */
		/* Most of the switcher.S doesn't care that it's been moved; on Intel,
		* jumps are relative, and it doesn't access any references to external
		* code or data.
		*
		* The only exception is the interrupt handlers in switcher.S: their
		* addresses are placed in a table (default_idt_entries), so we need to
		* update the table with the new addresses. switcher_offset() is a
		* convenience function which returns the distance between the builtin
		* switcher code and the high-mapped copy we just made. */
		for (i = 0; i < IDT_ENTRIES; i++)
		default_idt_entries[i] += switcher_offset();

		/*
		* Set up the Switcher's per-cpu areas.
		*
		* Each CPU gets two pages of its own within the high-mapped region
		* (aka. "struct lguest_pages"). Much of this can be initialized now,
		* but some depends on what Guest we are running (which is set up in
		* copy_in_guest_info()).
		*/
		for_each_possible_cpu(i) {
		/* lguest_pages() returns this CPU's two pages. */
		struct lguest_pages *pages = lguest_pages(i);
		/* This is a convenience pointer to make the code fit one
		* statement to a line. */
		struct lguest_ro_state *state = &pages->state;

		/* These fields are static: rest done in copy_in_guest_info */
		/* The Global Descriptor Table: the Host has a different one
		* for each CPU. We keep a descriptor for the GDT which says
		* where it is and how big it is (the size is actually the last
		* byte, not the size, hence the "-1"). */
		state->host_gdt_desc.size = GDT_SIZE-1;
		state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);

		/* All CPUs on the Host use the same Interrupt Descriptor
		* Table, so we just use store_idt(), which gets this CPU's IDT
		* descriptor. */
		store_idt(&state->host_idt_desc);

		/* The descriptors for the Guest's GDT and IDT can be filled
		* out now, too. We copy the GDT & IDT into ->guest_gdt and
		* ->guest_idt before actually running the Guest. */
		state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
		state->guest_idt_desc.address = (long)&state->guest_idt;
		state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
		state->guest_gdt_desc.address = (long)&state->guest_gdt;

		/* We know where we want the stack to be when the Guest enters
		* the switcher: in pages->regs. The stack grows upwards, so
		* we start it at the end of that structure. */
		state->guest_tss.esp0 = (long)(&pages->regs + 1);
		/* And this is the GDT entry to use for the stack: we keep a
		* couple of special LGUEST entries. */
		state->guest_tss.ss0 = LGUEST_DS;
		/* No I/O for you! */

		/* x86 can have a finegrained bitmap which indicates what I/O
		* ports the process can use. We set it to the end of our
		* structure, meaning "none". */
		state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);

		/* Some GDT entries are the same across all Guests, so we can
		* set them up now. */
		setup_default_gdt_entries(state);
		/* Most IDT entries are the same for all Guests, too.*/
		setup_default_idt_entries(state, default_idt_entries);

		/* Setup LGUEST segments on all cpus */
		/* The Host needs to be able to use the LGUEST segments on this
		* CPU, too, so put them in the Host GDT. */
		get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
		get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
		}

		/* Initialize entry point into switcher. */
		/* In the Switcher, we want the %cs segment register to use the
		* LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
		* it will be undisturbed when we switch. To change %cs and jump we
		* need this structure to feed to Intel's "lcall" instruction. */
		lguest_entry.offset = (long)switch_to_guest + switcher_offset();
		lguest_entry.segment = LGUEST_CS;

		printk(KERN_INFO "lguest: mapped switcher at %p\n",
		switcher_vma->addr);
		/* And we succeeded... */
		return 0;

		free_vma:
		@@ -149,35 +232,58 @@ free_some_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(switcher_page[i], 0);
		}

		/* IN/OUT insns: enough to get us past boot-time probing. */
		/*H:130 Our Guest is usually so well behaved; it never tries to do things it
		* isn't allowed to. Unfortunately, "struct paravirt_ops" isn't quite
		* complete, because it doesn't contain replacements for the Intel I/O
		* instructions. As a result, the Guest sometimes fumbles across one during
		* the boot process as it probes for various things which are usually attached
		* to a PC.
		*
		* When the Guest uses one of these instructions, we get trap #13 (General
		* Protection Fault) and come here. We see if it's one of those troublesome
		* instructions and skip over it. We return true if we did. */
		static int emulate_insn(struct lguest *lg)
		{
		u8 insn;
		unsigned int insnlen = 0, in = 0, shift = 0;
		/* The eip contains the virtual address of the Guest's instruction:
		* guest_pa just subtracts the Guest's page_offset. */
		unsigned long physaddr = guest_pa(lg, lg->regs->eip);

		/* This only works for addresses in linear mapping... */
		/* The guest_pa() function only works for Guest kernel addresses, but
		* that's all we're trying to do anyway. */
		if (lg->regs->eip < lg->page_offset)
		return 0;

		/* Decoding x86 instructions is icky. */
		lgread(lg, &insn, physaddr, 1);

		/* Operand size prefix means it's actually for ax. */
		/* 0x66 is an "operand prefix". It means it's using the upper 16 bits
		of the eax register. */
		if (insn == 0x66) {
		shift = 16;
		/* The instruction is 1 byte so far, read the next byte. */
		insnlen = 1;
		lgread(lg, &insn, physaddr + insnlen, 1);
		}

		/* We can ignore the lower bit for the moment and decode the 4 opcodes
		* we need to emulate. */
		switch (insn & 0xFE) {
		case 0xE4: /* in <next byte>,%al */
		insnlen += 2;
		@@ -194,9 +300,13 @@ static int emulate_insn(struct lguest *lg)
		insnlen += 1;
		break;
		default:
		/* OK, we don't know what this is, can't emulate. */
		return 0;
		}

		/* If it was an "IN" instruction, they expect the result to be read
		* into %eax, so we change %eax. We always return all-ones, which
		* traditionally means "there's nothing there". */
		if (in) {
		/* Lower bit tells is whether it's a 16 or 32 bit access */
		if (insn & 0x1)
		@@ -204,9 +314,12 @@ static int emulate_insn(struct lguest *lg)
		else
		lg->regs->eax \|= (0xFFFF << shift);
		}
		/* Finally, we've "done" the instruction, so move past it. */
		lg->regs->eip += insnlen;
		/* Success! */
		return 1;
		}
		/:/

		/*L:305
		* Dealing With Guest Memory.
		@@ -321,13 +434,24 @@ static void run_guest_once(struct lguest lg, struct lguest_pages pages)
		: "memory", "%edx", "%ecx", "%edi", "%esi");
		}

		/*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 lguest lg, unsigned long __user user)
		{
		/* We stop running once the Guest is dead. */
		while (!lg->dead) {
		/* We need to initialize this, otherwise gcc complains. It's
		* not (yet) clever enough to see that it's initialized when we
		* need it. */
		unsigned int cr2 = 0; /* Damn gcc */

		/* Hypercalls first: we might have been out to userspace */
		/* First we run any hypercalls the Guest wants done: either in
		* the hypercall ring in "struct lguest_data", or directly by
		* using int 31 (LGUEST_TRAP_ENTRY). */
		do_hypercalls(lg);
		/* It's possible the Guest did a SEND_DMA hypercall to the
		* Launcher, in which case we return from the read() now. */
		if (lg->dma_is_pending) {
		if (put_user(lg->pending_dma, user) \|\|
		put_user(lg->pending_key, user+1))
		@@ -335,6 +459,7 @@ int run_guest(struct lguest lg, unsigned long __user user)
		return sizeof(unsigned long)*2;
		}

		/* Check for signals */
		if (signal_pending(current))
		return -ERESTARTSYS;

		@@ -342,77 +467,154 @@ int run_guest(struct lguest lg, unsigned long __user user)
		if (lg->break_out)
		return -EAGAIN;

		/* 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. */
		maybe_do_interrupt(lg);

		/* 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();

		/* Just make absolutely sure the Guest is still alive. One of
		* those hypercalls could have been fatal, for example. */
		if (lg->dead)
		break;

		/* If the Guest asked to be stopped, we sleep. The Guest's
		* clock timer or LHCALL_BREAK from the Waker will wake us. */
		if (lg->halted) {
		set_current_state(TASK_INTERRUPTIBLE);
		schedule();
		continue;
		}

		/* OK, now we're ready to jump into the Guest. First we put up
		* the "Do Not Disturb" sign: */
		local_irq_disable();

		/* Even if we don't want FPU trap, guest might... */
		/* Remember the awfully-named TS bit? If the Guest has asked
		* to set it we set it now, so we can trap and pass that trap
		* to the Guest if it uses the FPU. */
		if (lg->ts)
		set_ts();

		/* Don't let Guest do SYSENTER: we can't handle it. */
		/* SYSENTER is an optimized way of doing system calls. We
		* can't allow it because it always jumps to privilege level 0.
		* A normal Guest won't try it because we don't advertise it in
		* CPUID, but a malicious Guest (or malicious Guest userspace
		* program) could, so we tell the CPU to disable it before
		* running the Guest. */
		if (boot_cpu_has(X86_FEATURE_SEP))
		wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);

		/* Now we actually run the Guest. It will pop back out when
		* something interesting happens, and we can examine its
		* registers to see what it was doing. */
		run_guest_once(lg, lguest_pages(raw_smp_processor_id()));

		/* Save cr2 now if we page-faulted. */
		/* The "regs" pointer contains two extra entries which are not
		* really registers: a trap number which says what interrupt or
		* trap made the switcher code come back, and an error code
		* which some traps set. */

		/* If the Guest page faulted, then the cr2 register will tell
		* us the bad virtual address. We have to grab this now,
		* because once we re-enable interrupts an interrupt could
		* fault and thus overwrite cr2, or we could even move off to a
		* different CPU. */
		if (lg->regs->trapnum == 14)
		cr2 = read_cr2();
		/* Similarly, if we took a trap because the Guest used the FPU,
		* we have to restore the FPU it expects to see. */
		else if (lg->regs->trapnum == 7)
		math_state_restore();

		/* Restore SYSENTER if it's supposed to be on. */
		if (boot_cpu_has(X86_FEATURE_SEP))
		wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);

		/* Now we're ready to be interrupted or moved to other CPUs */
		local_irq_enable();

		/* OK, so what happened? */
		switch (lg->regs->trapnum) {
		case 13: /* We've intercepted a GPF. */
		/* Check if this was one of those annoying IN or OUT
		* instructions which we need to emulate. If so, we
		* just go back into the Guest after we've done it. */
		if (lg->regs->errcode == 0) {
		if (emulate_insn(lg))
		continue;
		}
		break;
		case 14: /* We've intercepted a page fault. */
		/* The Guest accessed a virtual address that wasn't
		* mapped. This happens a lot: we don't actually set
		* up most of the page tables for the Guest at all when
		* we start: as it runs it asks for more and more, and
		* we set them up as required. In this case, we don't
		* even tell the Guest that the fault happened.
		*
		* The errcode tells whether this was a read or a
		* write, and whether kernel or userspace code. */
		if (demand_page(lg, cr2, lg->regs->errcode))
		continue;

		/* If lguest_data is NULL, this won't hurt. */
		/* OK, it's really not there (or not OK): the Guest
		* needs to know. We write out the cr2 value so it
		* knows where the fault occurred.
		*
		* Note that if the Guest were really messed up, this
		* could happen before it's done the INITIALIZE
		* hypercall, so lg->lguest_data will be NULL, so
		* &lg->lguest_data->cr2 will be address 8. Writing
		* into that address won't hurt the Host at all,
		* though. */
		if (put_user(cr2, &lg->lguest_data->cr2))
		kill_guest(lg, "Writing cr2");
		break;
		case 7: /* We've intercepted a Device Not Available fault. */
		/* If they don't want to know, just absorb it. */
		/* If the Guest doesn't want to know, we already
		* restored the Floating Point Unit, so we just
		* continue without telling it. */
		if (!lg->ts)
		continue;
		break;
		case 32 ... 255: /* Real interrupt, fall thru */
		case 32 ... 255:
		/* These values mean a real interrupt occurred, in
		* which case the Host handler has already been run.
		* We just do a friendly check if another process
		* should now be run, then fall through to loop
		* around: */
		cond_resched();
		case LGUEST_TRAP_ENTRY: /* Handled at top of loop */
		continue;
		}

		/* If we get here, it's a trap the Guest wants to know
		* about. */
		if (deliver_trap(lg, lg->regs->trapnum))
		continue;

		/* If the Guest doesn't have a handler (either it hasn't
		* registered any yet, or it's one of the faults we don't let
		* it handle), it dies with a cryptic error message. */
		kill_guest(lg, "unhandled trap %li at %#lx (%#lx)",
		lg->regs->trapnum, lg->regs->eip,
		lg->regs->trapnum == 14 ? cr2 : lg->regs->errcode);
		}
		/* The Guest is dead => "No such file or directory" */
		return -ENOENT;
		}

		/* Now we can look at each of the routines this calls, in increasing order of
		* complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
		* deliver_trap() and demand_page(). After all those, we'll be ready to
		* examine the Switcher, and our philosophical understanding of the Host/Guest
		* duality will be complete. :*/

		int find_free_guest(void)
		{
		unsigned int i;
		@@ -430,55 +632,96 @@ static void adjust_pge(void *on)
		write_cr4(read_cr4() & ~X86_CR4_PGE);
		}

		/*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 (paravirt_enabled()) {
		printk("lguest is afraid of %s\n", paravirt_ops.name);
		return -EPERM;
		}

		/* First we put the Switcher up in very high virtual memory. */
		err = map_switcher();
		if (err)
		return err;

		/* Now we set up the pagetable implementation for the Guests. */
		err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
		if (err) {
		unmap_switcher();
		return err;
		}

		/* The I/O subsystem needs some things initialized. */
		lguest_io_init();

		/* /dev/lguest needs to be registered. */
		err = lguest_device_init();
		if (err) {
		free_pagetables();
		unmap_switcher();
		return err;
		}

		/* Finally, we need to turn off "Page Global Enable". PGE is an
		* optimization where page table entries are specially marked to show
		* they never change. The Host kernel marks all the kernel pages this
		* way because it's always present, even when userspace is running.
		*
		* Lguest breaks this: unbeknownst to the rest of the Host kernel, we
		* switch to the Guest kernel. If you don't disable this on all CPUs,
		* you'll get really weird bugs that you'll chase for two days.
		*
		* I used to turn PGE off every time we switched to the Guest and back
		* on when we return, but that slowed the Switcher down noticibly. */

		/* We don't need the complexity of CPUs coming and going while we're
		* doing this. */
		lock_cpu_hotplug();
		if (cpu_has_pge) { /* We have a broader idea of "global". */
		/* Remember that this was originally set (for cleanup). */
		cpu_had_pge = 1;
		/* adjust_pge is a helper function which sets or unsets the PGE
		* bit on its CPU, depending on the argument (0 == unset). */
		on_each_cpu(adjust_pge, (void *)0, 0, 1);
		/* Turn off the feature in the global feature set. */
		clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
		}
		unlock_cpu_hotplug();

		/* All good! */
		return 0;
		}

		/* Cleaning up is just the same code, backwards. With a little French. */
		static void __exit fini(void)
		{
		lguest_device_remove();
		free_pagetables();
		unmap_switcher();

		/* If we had PGE before we started, turn it back on now. */
		lock_cpu_hotplug();
		if (cpu_had_pge) {
		set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
		/* adjust_pge's argument "1" means set PGE. */
		on_each_cpu(adjust_pge, (void *)1, 0, 1);
		}
		unlock_cpu_hotplug();
		}

		/* 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");

drivers/lguest/hypercalls.c

+108 −10

File changed.

Preview size limit exceeded, changes collapsed.

drivers/lguest/interrupts_and_traps.c

+157 −19

File changed.

Preview size limit exceeded, changes collapsed.

drivers/lguest/lg.h

+16 −3

Original line number	Diff line number	Diff line
		@@ -58,9 +58,18 @@ struct lguest_dma_info
		u8 interrupt; /* 0 when not registered */
		};

		/* We have separate types for the guest's ptes & pgds and the shadow ptes &
		* pgds. Since this host might use three-level pagetables and the guest and
		* shadow pagetables don't, we can't use the normal pte_t/pgd_t. */
		/*H:310 The page-table code owes a great debt of gratitude to Andi Kleen. He
		* reviewed the original code which used "u32" for all page table entries, and
		* insisted that it would be far clearer with explicit typing. I thought it
		* was overkill, but he was right: it is much clearer than it was before.
		*
		* We have separate types for the Guest's ptes & pgds and the shadow ptes &
		* pgds. There's already a Linux type for these (pte_t and pgd_t) but they
		* change depending on kernel config options (PAE). */

		/* Each entry is identical: lower 12 bits of flags and upper 20 bits for the
		* "page frame number" (0 == first physical page, etc). They are different
		* types so the compiler will warn us if we mix them improperly. */
		typedef union {
		struct { unsigned flags:12, pfn:20; };
		struct { unsigned long val; } raw;
		@@ -77,8 +86,12 @@ typedef union {
		struct { unsigned flags:12, pfn:20; };
		struct { unsigned long val; } raw;
		} gpte_t;

		/* We have two convenient macros to convert a "raw" value as handed to us by
		* the Guest into the correct Guest PGD or PTE type. */
		#define mkgpte(_val) ((gpte_t){.raw.val = _val})
		#define mkgpgd(_val) ((gpgd_t){.raw.val = _val})
		/:/

		struct pgdir
		{

drivers/lguest/page_tables.c

+286 −28

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