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: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 43 insertions, 90 deletions

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index f7a16b4ea456..42e87bf14113 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -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.
-         */
-        if (insn == 0xfa) {
-                /* "cli", or Clear Interrupt Enable instruction.  Skip it. */
-                cpu->regs->eip++;
-                return 1;
+/*
+ * 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.
+ */
+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. */
@@ -410,14 +367,10 @@ 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))
-                                return;
+                        setup_emulate_insn(cpu);
+                        return;
                 }
                 break;
         case 14: /* We've intercepted a Page Fault. */