diff options
Diffstat (limited to 'drivers/lguest/segments.c')
| -rw-r--r-- | drivers/lguest/segments.c | 62 |
1 files changed, 5 insertions, 57 deletions
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c index f675a41..9b81119 100644 --- a/drivers/lguest/segments.c +++ b/drivers/lguest/segments.c @@ -43,22 +43,6 @@ * begin. */ -/* Is the descriptor the Guest wants us to put in OK? - * - * The flag which Intel says must be zero: must be zero. The descriptor must - * be present, (this is actually checked earlier but is here for thorougness), - * and the descriptor type must be 1 (a memory segment). */ -static int desc_ok(const struct desc_struct *gdt) -{ - return ((gdt->b & 0x00209000) == 0x00009000); -} - -/* Is the segment present? (Otherwise it can't be used by the Guest). */ -static int segment_present(const struct desc_struct *gdt) -{ - return gdt->b & 0x8000; -} - /* 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 @@ -71,37 +55,11 @@ static int ignored_gdt(unsigned int num) || num == GDT_ENTRY_DOUBLEFAULT_TSS); } -/* If the Guest asks us to remove an entry from the GDT, we have to be careful. - * If one of the segment registers is pointing at that entry the Switcher will - * crash when it tries to reload the segment registers for the Guest. - * - * It doesn't make much sense for the Guest to try to remove its own code, data - * or stack segments while they're in use: assume that's a Guest bug. If it's - * one of the lesser segment registers using the removed entry, we simply set - * that register to 0 (unusable). */ -static void check_segment_use(struct lguest *lg, unsigned int desc) -{ - /* GDT entries are 8 bytes long, so we divide to get the index and - * ignore the bottom bits. */ - if (lg->regs->gs / 8 == desc) - lg->regs->gs = 0; - if (lg->regs->fs / 8 == desc) - lg->regs->fs = 0; - if (lg->regs->es / 8 == desc) - lg->regs->es = 0; - if (lg->regs->ds / 8 == desc - || lg->regs->cs / 8 == desc - || lg->regs->ss / 8 == desc) - kill_guest(lg, "Removed live GDT entry %u", desc); -} -/*:*/ -/*M:009 We wouldn't need to check for removal of in-use segments if we handled - * faults in the Switcher. However, it's probably not a worthwhile - * optimization. :*/ - -/*H:610 Once the GDT has been changed, we look through the changed entries and - * see if they're OK. If not, we'll call kill_guest() and the Guest will never - * get to use the invalid entries. */ +/*H:610 Once the GDT has been changed, we fix the new entries 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) { unsigned int i; @@ -112,16 +70,6 @@ static void fixup_gdt_table(struct lguest *lg, unsigned start, unsigned end) if (ignored_gdt(i)) continue; - /* We could fault in switch_to_guest if they are using - * a removed segment. */ - if (!segment_present(&lg->gdt[i])) { - check_segment_use(lg, i); - continue; - } - - if (!desc_ok(&lg->gdt[i])) - kill_guest(lg, "Bad GDT descriptor %i", i); - /* 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. */ |
