summaryrefslogtreecommitdiff
path: root/drivers/lguest/segments.c
diff options
context:
space:
mode:
Diffstat (limited to 'drivers/lguest/segments.c')
-rw-r--r--drivers/lguest/segments.c228
1 files changed, 0 insertions, 228 deletions
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c
deleted file mode 100644
index c4fb424dfddb..000000000000
--- a/drivers/lguest/segments.c
+++ /dev/null
@@ -1,228 +0,0 @@
-/*P:600
- * The x86 architecture has segments, which involve a table of descriptors
- * which can be used to do funky things with virtual address interpretation.
- * We originally used to use segments so the Guest couldn't alter the
- * Guest<->Host Switcher, and then we had to trim Guest segments, and restore
- * for userspace per-thread segments, but trim again for on userspace->kernel
- * transitions... This nightmarish creation was contained within this file,
- * where we knew not to tread without heavy armament and a change of underwear.
- *
- * In these modern times, the segment handling code consists of simple sanity
- * checks, and the worst you'll experience reading this code is butterfly-rash
- * from frolicking through its parklike serenity.
-:*/
-#include "lg.h"
-
-/*H:600
- * Segments & The Global Descriptor Table
- *
- * (That title sounds like a bad Nerdcore group. Not to suggest that there are
- * any good Nerdcore groups, but in high school a friend of mine had a band
- * called Joe Fish and the Chips, so there are definitely worse band names).
- *
- * To refresh: the GDT is a table of 8-byte values describing segments. Once
- * set up, these segments can be loaded into one of the 6 "segment registers".
- *
- * GDT entries are passed around as "struct desc_struct"s, which like IDT
- * entries are split into two 32-bit members, "a" and "b". One day, someone
- * will clean that up, and be declared a Hero. (No pressure, I'm just saying).
- *
- * Anyway, the GDT entry contains a base (the start address of the segment), a
- * limit (the size of the segment - 1), and some flags. Sounds simple, and it
- * would be, except those zany Intel engineers decided that it was too boring
- * to put the base at one end, the limit at the other, and the flags in
- * between. They decided to shotgun the bits at random throughout the 8 bytes,
- * like so:
- *
- * 0 16 40 48 52 56 63
- * [ limit part 1 ][ base part 1 ][ flags ][li][fl][base ]
- * mit ags part 2
- * part 2
- *
- * As a result, this file contains a certain amount of magic numeracy. Let's
- * begin.
- */
-
-/*
- * There are several entries we don't let the Guest set. The TSS entry is the
- * "Task State Segment" which controls all kinds of delicate things. The
- * LGUEST_CS and LGUEST_DS entries are reserved for the Switcher, and the
- * the Guest can't be trusted to deal with double faults.
- */
-static bool ignored_gdt(unsigned int num)
-{
- return (num == GDT_ENTRY_TSS
- || num == GDT_ENTRY_LGUEST_CS
- || num == GDT_ENTRY_LGUEST_DS
- || num == GDT_ENTRY_DOUBLEFAULT_TSS);
-}
-
-/*H:630
- * Once the Guest gave us new GDT entries, we fix them up a little. We
- * don't care if they're invalid: the worst that can happen is a General
- * Protection Fault in the Switcher when it restores a Guest segment register
- * which tries to use that entry. Then we kill the Guest for causing such a
- * mess: the message will be "unhandled trap 256".
- */
-static void fixup_gdt_table(struct lg_cpu *cpu, unsigned start, unsigned end)
-{
- unsigned int i;
-
- for (i = start; i < end; i++) {
- /*
- * We never copy these ones to real GDT, so we don't care what
- * they say
- */
- if (ignored_gdt(i))
- continue;
-
- /*
- * Segment descriptors contain a privilege level: the Guest is
- * sometimes careless and leaves this as 0, even though it's
- * running at privilege level 1. If so, we fix it here.
- */
- if (cpu->arch.gdt[i].dpl == 0)
- cpu->arch.gdt[i].dpl |= GUEST_PL;
-
- /*
- * Each descriptor has an "accessed" bit. If we don't set it
- * now, the CPU will try to set it when the Guest first loads
- * that entry into a segment register. But the GDT isn't
- * writable by the Guest, so bad things can happen.
- */
- cpu->arch.gdt[i].type |= 0x1;
- }
-}
-
-/*H:610
- * Like the IDT, we never simply use the GDT the Guest gives us. We keep
- * a GDT for each CPU, and copy across the Guest's entries each time we want to
- * run the Guest on that CPU.
- *
- * This routine is called at boot or modprobe time for each CPU to set up the
- * constant GDT entries: the ones which are the same no matter what Guest we're
- * running.
- */
-void setup_default_gdt_entries(struct lguest_ro_state *state)
-{
- struct desc_struct *gdt = state->guest_gdt;
- unsigned long tss = (unsigned long)&state->guest_tss;
-
- /* The Switcher segments are full 0-4G segments, privilege level 0 */
- gdt[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
- gdt[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
-
- /*
- * The TSS segment refers to the TSS entry for this particular CPU.
- */
- gdt[GDT_ENTRY_TSS].a = 0;
- gdt[GDT_ENTRY_TSS].b = 0;
-
- gdt[GDT_ENTRY_TSS].limit0 = 0x67;
- gdt[GDT_ENTRY_TSS].base0 = tss & 0xFFFF;
- gdt[GDT_ENTRY_TSS].base1 = (tss >> 16) & 0xFF;
- gdt[GDT_ENTRY_TSS].base2 = tss >> 24;
- gdt[GDT_ENTRY_TSS].type = 0x9; /* 32-bit TSS (available) */
- gdt[GDT_ENTRY_TSS].p = 0x1; /* Entry is present */
- gdt[GDT_ENTRY_TSS].dpl = 0x0; /* Privilege level 0 */
- gdt[GDT_ENTRY_TSS].s = 0x0; /* system segment */
-
-}
-
-/*
- * This routine sets up the initial Guest GDT for booting. All entries start
- * as 0 (unusable).
- */
-void setup_guest_gdt(struct lg_cpu *cpu)
-{
- /*
- * Start with full 0-4G segments...except the Guest is allowed to use
- * them, so set the privilege level appropriately in the flags.
- */
- cpu->arch.gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT;
- cpu->arch.gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT;
- cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].dpl |= GUEST_PL;
- cpu->arch.gdt[GDT_ENTRY_KERNEL_DS].dpl |= GUEST_PL;
-}
-
-/*H:650
- * An optimization of copy_gdt(), for just the three "thead-local storage"
- * entries.
- */
-void copy_gdt_tls(const struct lg_cpu *cpu, struct desc_struct *gdt)
-{
- unsigned int i;
-
- for (i = GDT_ENTRY_TLS_MIN; i <= GDT_ENTRY_TLS_MAX; i++)
- gdt[i] = cpu->arch.gdt[i];
-}
-
-/*H:640
- * When the Guest is run on a different CPU, or the GDT entries have changed,
- * copy_gdt() is called to copy the Guest's GDT entries across to this CPU's
- * GDT.
- */
-void copy_gdt(const struct lg_cpu *cpu, struct desc_struct *gdt)
-{
- unsigned int i;
-
- /*
- * The default entries from setup_default_gdt_entries() are not
- * replaced. See ignored_gdt() above.
- */
- for (i = 0; i < GDT_ENTRIES; i++)
- if (!ignored_gdt(i))
- gdt[i] = cpu->arch.gdt[i];
-}
-
-/*H:620
- * This is where the Guest asks us to load a new GDT entry
- * (LHCALL_LOAD_GDT_ENTRY). We tweak the entry and copy it in.
- */
-void load_guest_gdt_entry(struct lg_cpu *cpu, u32 num, u32 lo, u32 hi)
-{
- /*
- * We assume the Guest has the same number of GDT entries as the
- * Host, otherwise we'd have to dynamically allocate the Guest GDT.
- */
- if (num >= ARRAY_SIZE(cpu->arch.gdt)) {
- kill_guest(cpu, "too many gdt entries %i", num);
- return;
- }
-
- /* Set it up, then fix it. */
- cpu->arch.gdt[num].a = lo;
- cpu->arch.gdt[num].b = hi;
- fixup_gdt_table(cpu, num, num+1);
- /*
- * Mark that the GDT changed so the core knows it has to copy it again,
- * even if the Guest is run on the same CPU.
- */
- cpu->changed |= CHANGED_GDT;
-}
-
-/*
- * This is the fast-track version for just changing the three TLS entries.
- * Remember that this happens on every context switch, so it's worth
- * optimizing. But wouldn't it be neater to have a single hypercall to cover
- * both cases?
- */
-void guest_load_tls(struct lg_cpu *cpu, unsigned long gtls)
-{
- struct desc_struct *tls = &cpu->arch.gdt[GDT_ENTRY_TLS_MIN];
-
- __lgread(cpu, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES);
- fixup_gdt_table(cpu, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1);
- /* Note that just the TLS entries have changed. */
- cpu->changed |= CHANGED_GDT_TLS;
-}
-
-/*H:660
- * With this, we have finished the Host.
- *
- * Five of the seven parts of our task are complete. You have made it through
- * the Bit of Despair (I think that's somewhere in the page table code,
- * myself).
- *
- * Next, we examine "make Switcher". It's short, but intense.
- */