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Commit c565650b authored by Rusty Russell's avatar Rusty Russell
Browse files

lguest: send trap 13 through to userspace. 



We copy 7 bytes at eip for userspace's instruction decode; we have to
carefully handle the case where eip is at the end of a page.  We can't
leave this to userspace since kernel has all the page table decode
logic.

The decode logic moves to userspace, basically unchanged.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent c9e433e4

drivers/lguest/x86/core.c

+43 −90
Original line number Diff line number Diff line
@@ -314,95 +314,52 @@ void lguest_arch_run_guest(struct lg_cpu *cpu) 
 * usually attached to a PC.

 *

 * When the Guest uses one of these instructions, we get a trap (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.

 * Protection Fault) and come here.  We queue this to be sent out to the

 * Launcher to handle.

 */

static int emulate_insn(struct lg_cpu *cpu)

{

	u8 insn;

	unsigned int insnlen = 0, in = 0, small_operand = 0;

	/*

	 * The eip contains the *virtual* address of the Guest's instruction:

	 * walk the Guest's page tables to find the "physical" address.

	 */

	unsigned long physaddr = guest_pa(cpu, cpu->regs->eip);



	/*

	 * This must be the Guest kernel trying to do something, not userspace!

	 * The bottom two bits of the CS segment register are the privilege

	 * level.

	 */

	if ((cpu->regs->cs & 3) != GUEST_PL)

		return 0;



	/* Decoding x86 instructions is icky. */

	insn = lgread(cpu, physaddr, u8);



/*

	 * Around 2.6.33, the kernel started using an emulation for the

	 * cmpxchg8b instruction in early boot on many configurations.  This

	 * code isn't paravirtualized, and it tries to disable interrupts.

	 * Ignore it, which will Mostly Work.

 * The eip contains the *virtual* address of the Guest's instruction:

 * we copy the instruction here so the Launcher doesn't have to walk

 * the page tables to decode it.  We handle the case (eg. in a kernel

 * module) where the instruction is over two pages, and the pages are

 * virtually but not physically contiguous.

 *

 * The longest possible x86 instruction is 15 bytes, but we don't handle

 * anything that strange.

 */

	if (insn == 0xfa) {

		/* "cli", or Clear Interrupt Enable instruction.  Skip it. */

		cpu->regs->eip++;

		return 1;

static void copy_from_guest(struct lg_cpu *cpu,

			    void *dst, unsigned long vaddr, size_t len)

{

	size_t to_page_end = PAGE_SIZE - (vaddr % PAGE_SIZE);

	unsigned long paddr;



	BUG_ON(len > PAGE_SIZE);



	/* If it goes over a page, copy in two parts. */

	if (len > to_page_end) {

		/* But make sure the next page is mapped! */

		if (__guest_pa(cpu, vaddr + to_page_end, &paddr))

			copy_from_guest(cpu, dst + to_page_end,

					vaddr + to_page_end,

					len - to_page_end);

		else

			/* Otherwise fill with zeroes. */

			memset(dst + to_page_end, 0, len - to_page_end);

		len = to_page_end;

	}



	/*

	 * 0x66 is an "operand prefix".  It means a 16, not 32 bit in/out.

	 */

	if (insn == 0x66) {

		small_operand = 1;

		/* The instruction is 1 byte so far, read the next byte. */

		insnlen = 1;

		insn = lgread(cpu, physaddr + insnlen, u8);

	/* This will kill the guest if it isn't mapped, but that

	 * shouldn't happen. */

	__lgread(cpu, dst, guest_pa(cpu, vaddr), len);

}



	/*

	 * 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;

		in = 1;

		break;

	case 0xEC: /* in     (%dx),%al */

		insnlen += 1;

		in = 1;

		break;

	case 0xE6: /* out    %al,<next byte> */

		insnlen += 2;

		break;

	case 0xEE: /* out    %al,(%dx) */

		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 means it's a 32/16 bit access */

		if (insn & 0x1) {

			if (small_operand)

				cpu->regs->eax |= 0xFFFF;

			else

				cpu->regs->eax = 0xFFFFFFFF;

		} else

			cpu->regs->eax |= 0xFF;

	}

	/* Finally, we've "done" the instruction, so move past it. */

	cpu->regs->eip += insnlen;

	/* Success! */

	return 1;

static void setup_emulate_insn(struct lg_cpu *cpu)

{

	cpu->pending.trap = 13;

	copy_from_guest(cpu, cpu->pending.insn, cpu->regs->eip,

			sizeof(cpu->pending.insn));

}



/*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
@@ -410,13 +367,9 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu) 
{

	switch (cpu->regs->trapnum) {

	case 13: /* We've intercepted a General Protection Fault. */

		/*

		 * 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.

		 */

		/* Hand to Launcher to emulate those pesky IN and OUT insns */

		if (cpu->regs->errcode == 0) {

			if (emulate_insn(cpu))

			setup_emulate_insn(cpu);

			return;

		}

		break;

tools/lguest/lguest.c

+149 −0
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ 
#include <signal.h>

#include <pwd.h>

#include <grp.h>

#include <sys/user.h>



#ifndef VIRTIO_F_ANY_LAYOUT

#define VIRTIO_F_ANY_LAYOUT		27
@@ -1143,6 +1144,150 @@ static void handle_output(unsigned long addr) 
	      strnlen(from_guest_phys(addr), guest_limit - addr));

}



/*L:216

 * This is where we emulate a handful of Guest instructions.  It's ugly

 * and we used to do it in the kernel but it grew over time.

 */



/*

 * We use the ptrace syscall's pt_regs struct to talk about registers

 * to lguest: these macros convert the names to the offsets.

 */

#define getreg(name) getreg_off(offsetof(struct user_regs_struct, name))

#define setreg(name, val) \

	setreg_off(offsetof(struct user_regs_struct, name), (val))



static u32 getreg_off(size_t offset)

{

	u32 r;

	unsigned long args[] = { LHREQ_GETREG, offset };



	if (pwrite(lguest_fd, args, sizeof(args), cpu_id) < 0)

		err(1, "Getting register %u", offset);

	if (pread(lguest_fd, &r, sizeof(r), cpu_id) != sizeof(r))

		err(1, "Reading register %u", offset);



	return r;

}



static void setreg_off(size_t offset, u32 val)

{

	unsigned long args[] = { LHREQ_SETREG, offset, val };



	if (pwrite(lguest_fd, args, sizeof(args), cpu_id) < 0)

		err(1, "Setting register %u", offset);

}



static void emulate_insn(const u8 insn[])

{

	unsigned long args[] = { LHREQ_TRAP, 13 };

	unsigned int insnlen = 0, in = 0, small_operand = 0, byte_access;

	unsigned int eax, port, mask;

	/*

	 * We always return all-ones on IO port reads, which traditionally

	 * means "there's nothing there".

	 */

	u32 val = 0xFFFFFFFF;



	/*

	 * This must be the Guest kernel trying to do something, not userspace!

	 * The bottom two bits of the CS segment register are the privilege

	 * level.

	 */

	if ((getreg(xcs) & 3) != 0x1)

		goto no_emulate;



	/* Decoding x86 instructions is icky. */



	/*

	 * Around 2.6.33, the kernel started using an emulation for the

	 * cmpxchg8b instruction in early boot on many configurations.  This

	 * code isn't paravirtualized, and it tries to disable interrupts.

	 * Ignore it, which will Mostly Work.

	 */

	if (insn[insnlen] == 0xfa) {

		/* "cli", or Clear Interrupt Enable instruction.  Skip it. */

		insnlen = 1;

		goto skip_insn;

	}



	/*

	 * 0x66 is an "operand prefix".  It means a 16, not 32 bit in/out.

	 */

	if (insn[insnlen] == 0x66) {

		small_operand = 1;

		/* The instruction is 1 byte so far, read the next byte. */

		insnlen = 1;

	}



	/* If the lower bit isn't set, it's a single byte access */

	byte_access = !(insn[insnlen] & 1);



	/*

	 * Now we can ignore the lower bit and decode the 4 opcodes

	 * we need to emulate.

	 */

	switch (insn[insnlen] & 0xFE) {

	case 0xE4: /* in     <next byte>,%al */

		port = insn[insnlen+1];

		insnlen += 2;

		in = 1;

		break;

	case 0xEC: /* in     (%dx),%al */

		port = getreg(edx) & 0xFFFF;

		insnlen += 1;

		in = 1;

		break;

	case 0xE6: /* out    %al,<next byte> */

		port = insn[insnlen+1];

		insnlen += 2;

		break;

	case 0xEE: /* out    %al,(%dx) */

		port = getreg(edx) & 0xFFFF;

		insnlen += 1;

		break;

	default:

		/* OK, we don't know what this is, can't emulate. */

		goto no_emulate;

	}



	/* Set a mask of the 1, 2 or 4 bytes, depending on size of IO */

	if (byte_access)

		mask = 0xFF;

	else if (small_operand)

		mask = 0xFFFF;

	else

		mask = 0xFFFFFFFF;



	/*

	 * If it was an "IN" instruction, they expect the result to be read

	 * into %eax, so we change %eax.

	 */

	eax = getreg(eax);



	if (in) {

		/* Clear the bits we're about to read */

		eax &= ~mask;

		/* Copy bits in from val. */

		eax |= val & mask;

		/* Now update the register. */

		setreg(eax, eax);

	}



	verbose("IO %s of %x to %u: %#08x\n",

		in ? "IN" : "OUT", mask, port, eax);

skip_insn:

	/* Finally, we've "done" the instruction, so move past it. */

	setreg(eip, getreg(eip) + insnlen);

	return;



no_emulate:

	/* Inject trap into Guest. */

	if (write(lguest_fd, args, sizeof(args)) < 0)

		err(1, "Reinjecting trap 13 for fault at %#x", getreg(eip));

}





/*L:190

 * Device Setup

 *
@@ -1832,6 +1977,10 @@ static void __attribute__((noreturn)) run_guest(void) 
				verbose("Notify on address %#08x\n",

					notify.addr);

				handle_output(notify.addr);

			} else if (notify.trap == 13) {

				verbose("Emulating instruction at %#x\n",

					getreg(eip));

				emulate_insn(notify.insn);

			} else

				errx(1, "Unknown trap %i addr %#08x\n",

				     notify.trap, notify.addr);