diff options
Diffstat (limited to 'drivers/lguest/segments.c')
| -rw-r--r-- | drivers/lguest/segments.c | 189 |
1 files changed, 120 insertions, 69 deletions
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c index 9b81119f46e..c4fb424dfdd 100644 --- a/drivers/lguest/segments.c +++ b/drivers/lguest/segments.c @@ -1,4 +1,5 @@ -/*P:600 The x86 architecture has segments, which involve a table of descriptors +/*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 @@ -8,12 +9,11 @@ * * 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. :*/ + * from frolicking through its parklike serenity. +:*/ #include "lg.h" /*H:600 - * We've almost completed the Host; there's just one file to go! - * * Segments & The Global Descriptor Table * * (That title sounds like a bad Nerdcore group. Not to suggest that there are @@ -43,11 +43,13 @@ * begin. */ -/* There are several entries we don't let the Guest set. The TSS entry is the +/* + * 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 int ignored_gdt(unsigned int num) + * 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 @@ -55,118 +57,167 @@ static int ignored_gdt(unsigned int num) || num == GDT_ENTRY_DOUBLEFAULT_TSS); } -/*H:610 Once the GDT has been changed, we fix the new entries up a little. We +/*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 lguest *lg, unsigned start, unsigned end) + * 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 */ + /* + * 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 + /* + * 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 ((lg->gdt[i].b & 0x00006000) == 0) - lg->gdt[i].b |= (GUEST_PL << 13); + * 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 + /* + * 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. */ - lg->gdt[i].b |= 0x00000100; + * writable by the Guest, so bad things can happen. + */ + cpu->arch.gdt[i].type |= 0x1; } } -/* This routine is called at boot or modprobe time for each CPU to set up the - * "constant" GDT entries for Guests running on that CPU. */ +/*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 hypervisor segments are full 0-4G segments, privilege level 0 */ + /* 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 CPU, so we cannot - * copy it from the Guest. Forgive the magic flags */ - gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16); - gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000) - | ((tss >> 16) & 0x000000FF); + /* + * 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 is called before the Guest is run for the first time. */ -void setup_guest_gdt(struct lguest *lg) +/* + * 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... */ - lg->gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT; - lg->gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT; - /* ...except the Guest is allowed to use them, so set the privilege - * level appropriately in the flags. */ - lg->gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13); - lg->gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13); + /* + * 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; } -/* Like the IDT, we never simply use the GDT the Guest gives us. We set up the - * GDTs for each CPU, then we copy across the entries each time we want to run - * a different Guest on that CPU. */ - -/* A partial GDT load, for the three "thead-local storage" entries. Otherwise - * it's just like load_guest_gdt(). So much, in fact, it would probably be - * neater to have a single hypercall to cover both. */ -void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) +/*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] = lg->gdt[i]; + gdt[i] = cpu->arch.gdt[i]; } -/* This is the full version */ -void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) +/*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. */ + /* + * 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] = lg->gdt[i]; + gdt[i] = cpu->arch.gdt[i]; } -/* This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). */ -void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) +/*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(lg->gdt)) - kill_guest(lg, "too many gdt entries %i", num); - - /* We read the whole thing in, then fix it up. */ - lgread(lg, lg->gdt, table, num * sizeof(lg->gdt[0])); - fixup_gdt_table(lg, 0, ARRAY_SIZE(lg->gdt)); - /* 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. */ - lg->changed |= CHANGED_GDT; + /* + * 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; } -void guest_load_tls(struct lguest *lg, unsigned long gtls) +/* + * 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 = &lg->gdt[GDT_ENTRY_TLS_MIN]; + struct desc_struct *tls = &cpu->arch.gdt[GDT_ENTRY_TLS_MIN]; - lgread(lg, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES); - fixup_gdt_table(lg, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1); - lg->changed |= CHANGED_GDT_TLS; + __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 |