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, 149 insertions, 0 deletions

diff --git a/tools/lguest/lguest.c b/tools/lguest/lguest.c
index 0e754d04876d..b2217657f62c 100644
--- a/tools/lguest/lguest.c
+++ b/tools/lguest/lguest.c
@@ -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);