diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 0a46e8837d9a01629d708db246953a4af3f4600b..4a315f08a567d40a15735fa9091118a7b96f60eb 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -453,6 +453,11 @@ static void run_guest_once(struct lguest *lg, struct lguest_pages *pages)
* lguest_pages". */
copy_in_guest_info(lg, pages);
+ /* Set the trap number to 256 (impossible value). If we fault while
+ * switching to the Guest (bad segment registers or bug), this will
+ * cause us to abort the Guest. */
+ lg->regs->trapnum = 256;
+
/* Now: we push the "eflags" register on the stack, then do an "lcall".
* This is how we change from using the kernel code segment to using
* the dedicated lguest code segment, as well as jumping into the
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 49787e964a0dfcae6b03fa044aaf2c0a03fd2a04..49aa55577d0dec0e2543c2a8801b91ebc98b1359 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -195,13 +195,16 @@ static int has_err(unsigned int trap)
/* deliver_trap() returns true if it could deliver the trap. */
int deliver_trap(struct lguest *lg, unsigned int num)
{
- u32 lo = lg->idt[num].a, hi = lg->idt[num].b;
+ /* Trap numbers are always 8 bit, but we set an impossible trap number
+ * for traps inside the Switcher, so check that here. */
+ if (num >= ARRAY_SIZE(lg->idt))
+ return 0;
/* Early on the Guest hasn't set the IDT entries (or maybe it put a
* bogus one in): if we fail here, the Guest will be killed. */
- if (!idt_present(lo, hi))
+ if (!idt_present(lg->idt[num].a, lg->idt[num].b))
return 0;
- set_guest_interrupt(lg, lo, hi, has_err(num));
+ set_guest_interrupt(lg, lg->idt[num].a, lg->idt[num].b, has_err(num));
return 1;
}
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
index fb17d2757be972dff4f716f3b09b09e843d5517f..524beea7fb19b7fe659436dcbbdf3844619fe519 100644
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -323,9 +323,12 @@ static void lguest_write_gdt_entry(struct desc_struct *dt,
* __thread variables). So we have a hypercall specifically for this case. */
static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
{
+ /* There's one problem which normal hardware doesn't have: the Host
+ * can't handle us removing entries we're currently using. So we clear
+ * the GS register here: if it's needed it'll be reloaded anyway. */
+ loadsegment(gs, 0);
lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
}
-/*:*/
/*G:038 That's enough excitement for now, back to ploughing through each of
* the paravirt_ops (we're about 1/3 of the way through).
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c
index f675a41a80da57cdc11d5d4825d2c7ce84a9254f..9b81119f46e937ce9b9639fe4e74f65139288a51 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. */
diff --git a/drivers/lguest/switcher.S b/drivers/lguest/switcher.S
index d418179ea6b50a56fc4d488815aff51e7b3322c7..7c9c230cc845f184973e6eebea5beb9a41568735 100644
--- a/drivers/lguest/switcher.S
+++ b/drivers/lguest/switcher.S
@@ -47,6 +47,7 @@
// Down here in the depths of assembler code.
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
+#include <asm/page.h>
#include "lg.h"
// We mark the start of the code to copy
@@ -182,13 +183,15 @@ ENTRY(switch_to_guest)
movl $(LGUEST_DS), %eax; \
movl %eax, %ds; \
/* So where are we? Which CPU, which struct? \
- * The stack is our clue: our TSS sets \
- * It at the end of "struct lguest_pages" \
- * And we then pushed and pushed and pushed Guest regs: \
- * Now stack points atop the "struct lguest_regs". \
- * Subtract that offset, and we find our struct. */ \
+ * The stack is our clue: our TSS starts \
+ * It at the end of "struct lguest_pages". \
+ * Or we may have stumbled while restoring \
+ * Our Guest segment regs while in switch_to_guest, \
+ * The fault pushed atop that part-unwound stack. \
+ * If we round the stack down to the page start \
+ * We're at the start of "struct lguest_pages". */ \
movl %esp, %eax; \
- subl $LGUEST_PAGES_regs, %eax; \
+ andl $(~(1 << PAGE_SHIFT - 1)), %eax; \
/* Save our trap number: the switch will obscure it \
* (The Guest regs are not mapped here in the Host) \
* %ebx holds it safe for deliver_to_host */ \