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Diffstat (limited to 'drivers/lguest/segments.c')
| -rw-r--r-- | drivers/lguest/segments.c | 228 |
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. - */ |