lguest: don't share Switcher PTE pages between guests.
We currently use the whole top PGD entry for the switcher, so we
simply share a fixed page of PTEs between all guests (actually, it's
one per Host CPU, to ensure isolation between guests).
Changes to a scheme where every guest has its own mappings.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index b6c71c3..7e1d7ee 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -333,15 +333,10 @@
if (err)
goto out;
- /* Now we set up the pagetable implementation for the Guests. */
- err = init_pagetables(lg_switcher_pages);
- if (err)
- goto unmap;
-
/* We might need to reserve an interrupt vector. */
err = init_interrupts();
if (err)
- goto free_pgtables;
+ goto unmap;
/* /dev/lguest needs to be registered. */
err = lguest_device_init();
@@ -356,8 +351,6 @@
free_interrupts:
free_interrupts();
-free_pgtables:
- free_pagetables();
unmap:
unmap_switcher();
out:
@@ -369,7 +362,6 @@
{
lguest_device_remove();
free_interrupts();
- free_pagetables();
unmap_switcher();
lguest_arch_host_fini();
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 9a345ef..faac9fc 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -14,9 +14,6 @@
#include <asm/lguest.h>
-void free_pagetables(void);
-int init_pagetables(struct page **switcher_pages);
-
struct pgdir {
unsigned long gpgdir;
pgd_t *pgdir;
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 009c717..1f48f271 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -62,20 +62,11 @@
* will need the last pmd entry of the last pmd page.
*/
#ifdef CONFIG_X86_PAE
-#define SWITCHER_PMD_INDEX (PTRS_PER_PMD - 1)
#define CHECK_GPGD_MASK _PAGE_PRESENT
#else
#define CHECK_GPGD_MASK _PAGE_TABLE
#endif
-/*
- * We actually need a separate PTE page for each CPU. Remember that after the
- * Switcher code itself comes two pages for each CPU, and we don't want this
- * CPU's guest to see the pages of any other CPU.
- */
-static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
-#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
-
/*H:320
* The page table code is curly enough to need helper functions to keep it
* clear and clean. The kernel itself provides many of them; one advantage
@@ -714,9 +705,6 @@
int *blank_pgdir)
{
unsigned int next;
-#ifdef CONFIG_X86_PAE
- pmd_t *pmd_table;
-#endif
/*
* We pick one entry at random to throw out. Choosing the Least
@@ -731,29 +719,11 @@
if (!cpu->lg->pgdirs[next].pgdir)
next = cpu->cpu_pgd;
else {
-#ifdef CONFIG_X86_PAE
/*
- * In PAE mode, allocate a pmd page and populate the
- * last pgd entry.
+ * This is a blank page, so there are no kernel
+ * mappings: caller must map the stack!
*/
- pmd_table = (pmd_t *)get_zeroed_page(GFP_KERNEL);
- if (!pmd_table) {
- free_page((long)cpu->lg->pgdirs[next].pgdir);
- set_pgd(cpu->lg->pgdirs[next].pgdir, __pgd(0));
- next = cpu->cpu_pgd;
- } else {
- set_pgd(cpu->lg->pgdirs[next].pgdir +
- SWITCHER_PGD_INDEX,
- __pgd(__pa(pmd_table) | _PAGE_PRESENT));
- /*
- * This is a blank page, so there are no kernel
- * mappings: caller must map the stack!
- */
- *blank_pgdir = 1;
- }
-#else
*blank_pgdir = 1;
-#endif
}
}
/* Record which Guest toplevel this shadows. */
@@ -764,6 +734,23 @@
return next;
}
+/*H:501
+ * We do need the Switcher code mapped at all times, so we allocate that
+ * part of the Guest page table here, and populate it when we're about to run
+ * the guest.
+ */
+static bool allocate_switcher_mapping(struct lg_cpu *cpu)
+{
+ int i;
+
+ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
+ if (!find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
+ CHECK_GPGD_MASK, _PAGE_TABLE))
+ return false;
+ }
+ return true;
+}
+
/*H:470
* Finally, a routine which throws away everything: all PGD entries in all
* the shadow page tables, including the Guest's kernel mappings. This is used
@@ -774,28 +761,14 @@
unsigned int i, j;
/* Every shadow pagetable this Guest has */
- for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
- if (lg->pgdirs[i].pgdir) {
-#ifdef CONFIG_X86_PAE
- pgd_t *spgd;
- pmd_t *pmdpage;
- unsigned int k;
+ for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) {
+ if (!lg->pgdirs[i].pgdir)
+ continue;
- /* Get the last pmd page. */
- spgd = lg->pgdirs[i].pgdir + SWITCHER_PGD_INDEX;
- pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
-
- /*
- * And release the pmd entries of that pmd page,
- * except for the switcher pmd.
- */
- for (k = 0; k < SWITCHER_PMD_INDEX; k++)
- release_pmd(&pmdpage[k]);
-#endif
- /* Every PGD entry except the Switcher at the top */
- for (j = 0; j < SWITCHER_PGD_INDEX; j++)
- release_pgd(lg->pgdirs[i].pgdir + j);
- }
+ /* Every PGD entry. */
+ for (j = 0; j < PTRS_PER_PGD; j++)
+ release_pgd(lg->pgdirs[i].pgdir + j);
+ }
}
/*
@@ -809,6 +782,9 @@
release_all_pagetables(cpu->lg);
/* We need the Guest kernel stack mapped again. */
pin_stack_pages(cpu);
+ /* And we need Switcher allocated. */
+ if (!allocate_switcher_mapping(cpu))
+ kill_guest(cpu, "Cannot populate switcher mapping");
}
/*H:430
@@ -844,9 +820,15 @@
newpgdir = new_pgdir(cpu, pgtable, &repin);
/* Change the current pgd index to the new one. */
cpu->cpu_pgd = newpgdir;
- /* If it was completely blank, we map in the Guest kernel stack */
+ /*
+ * If it was completely blank, we map in the Guest kernel stack and
+ * the Switcher.
+ */
if (repin)
pin_stack_pages(cpu);
+
+ if (!allocate_switcher_mapping(cpu))
+ kill_guest(cpu, "Cannot populate switcher mapping");
}
/*:*/
@@ -976,14 +958,23 @@
{
int pgdir;
- if (idx >= SWITCHER_PGD_INDEX)
+ if (idx > PTRS_PER_PGD) {
+ kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
+ idx, PTRS_PER_PGD);
return;
+ }
/* If they're talking about a page table we have a shadow for... */
pgdir = find_pgdir(lg, gpgdir);
- if (pgdir < ARRAY_SIZE(lg->pgdirs))
+ if (pgdir < ARRAY_SIZE(lg->pgdirs)) {
/* ... throw it away. */
release_pgd(lg->pgdirs[pgdir].pgdir + idx);
+ /* That might have been the Switcher mapping, remap it. */
+ if (!allocate_switcher_mapping(&lg->cpus[0])) {
+ kill_guest(&lg->cpus[0],
+ "Cannot populate switcher mapping");
+ }
+ }
}
#ifdef CONFIG_X86_PAE
@@ -1001,6 +992,9 @@
* we will populate on future faults. The Guest doesn't have any actual
* pagetables yet, so we set linear_pages to tell demand_page() to fake it
* for the moment.
+ *
+ * We do need the Switcher to be mapped at all times, so we allocate that
+ * part of the Guest page table here.
*/
int init_guest_pagetable(struct lguest *lg)
{
@@ -1014,6 +1008,13 @@
/* We start with a linear mapping until the initialize. */
cpu->linear_pages = true;
+
+ /* Allocate the page tables for the Switcher. */
+ if (!allocate_switcher_mapping(cpu)) {
+ release_all_pagetables(lg);
+ return -ENOMEM;
+ }
+
return 0;
}
@@ -1065,92 +1066,69 @@
* (vi) Mapping the Switcher when the Guest is about to run.
*
* The Switcher and the two pages for this CPU need to be visible in the
- * Guest (and not the pages for other CPUs). We have the appropriate PTE pages
- * for each CPU already set up, we just need to hook them in now we know which
- * Guest is about to run on this CPU.
+ * Guest (and not the pages for other CPUs).
+ *
+ * The pages have all been allocate
*/
void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
{
- pte_t *switcher_pte_page = __this_cpu_read(switcher_pte_pages);
- pte_t regs_pte;
+ unsigned long base, i;
+ struct page *percpu_switcher_page, *regs_page;
+ pte_t *pte;
-#ifdef CONFIG_X86_PAE
- pmd_t switcher_pmd;
- pmd_t *pmd_table;
+ /* Code page should always be mapped, and executable. */
+ pte = find_spte(cpu, switcher_addr, false, 0, 0);
+ get_page(lg_switcher_pages[0]);
+ set_pte(pte, mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
- switcher_pmd = pfn_pmd(__pa(switcher_pte_page) >> PAGE_SHIFT,
- PAGE_KERNEL_EXEC);
+ /* Clear all the Switcher mappings for any other CPUs. */
+ /* FIXME: This is dumb: update only when Host CPU changes. */
+ for_each_possible_cpu(i) {
+ /* Get location of lguest_pages (indexed by Host CPU) */
+ base = switcher_addr + PAGE_SIZE
+ + i * sizeof(struct lguest_pages);
- /* Figure out where the pmd page is, by reading the PGD, and converting
- * it to a virtual address. */
- pmd_table = __va(pgd_pfn(cpu->lg->
- pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX])
- << PAGE_SHIFT);
- /* Now write it into the shadow page table. */
- set_pmd(&pmd_table[SWITCHER_PMD_INDEX], switcher_pmd);
-#else
- pgd_t switcher_pgd;
+ /* Get shadow PTE for first page (where we put guest regs). */
+ pte = find_spte(cpu, base, false, 0, 0);
+ set_pte(pte, __pte(0));
+
+ /* This is where we put R/O state. */
+ pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
+ set_pte(pte, __pte(0));
+ }
/*
- * Make the last PGD entry for this Guest point to the Switcher's PTE
- * page for this CPU (with appropriate flags).
+ * When we're running the Guest, we want the Guest's "regs" page to
+ * appear where the first Switcher page for this CPU is. This is an
+ * optimization: when the Switcher saves the Guest registers, it saves
+ * them into the first page of this CPU's "struct lguest_pages": if we
+ * make sure the Guest's register page is already mapped there, we
+ * don't have to copy them out again.
*/
- switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL_EXEC);
+ /* Find the shadow PTE for this regs page. */
+ base = switcher_addr + PAGE_SIZE
+ + raw_smp_processor_id() * sizeof(struct lguest_pages);
+ pte = find_spte(cpu, base, false, 0, 0);
+ regs_page = pfn_to_page(__pa(cpu->regs_page) >> PAGE_SHIFT);
+ get_page(regs_page);
+ set_pte(pte, mk_pte(regs_page, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL)));
- cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
-
-#endif
/*
- * We also change the Switcher PTE page. When we're running the Guest,
- * we want the Guest's "regs" page to appear where the first Switcher
- * page for this CPU is. This is an optimization: when the Switcher
- * saves the Guest registers, it saves them into the first page of this
- * CPU's "struct lguest_pages": if we make sure the Guest's register
- * page is already mapped there, we don't have to copy them out
- * again.
+ * We map the second page of the struct lguest_pages read-only in
+ * the Guest: the IDT, GDT and other things it's not supposed to
+ * change.
*/
- regs_pte = pfn_pte(__pa(cpu->regs_page) >> PAGE_SHIFT, PAGE_KERNEL);
- set_pte(&switcher_pte_page[pte_index((unsigned long)pages)], regs_pte);
+ base += PAGE_SIZE;
+ pte = find_spte(cpu, base, false, 0, 0);
+
+ percpu_switcher_page
+ = lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1];
+ get_page(percpu_switcher_page);
+ set_pte(pte, mk_pte(percpu_switcher_page,
+ __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)));
}
/*:*/
-static void free_switcher_pte_pages(void)
-{
- unsigned int i;
-
- for_each_possible_cpu(i)
- free_page((long)switcher_pte_page(i));
-}
-
-/*H:520
- * Setting up the Switcher PTE page for given CPU is fairly easy, given
- * the CPU number and the "struct page"s for the Switcher and per-cpu pages.
- */
-static __init void populate_switcher_pte_page(unsigned int cpu,
- struct page *switcher_pages[])
-{
- pte_t *pte = switcher_pte_page(cpu);
- int i;
-
- /* The first entries maps the Switcher code. */
- set_pte(&pte[0], mk_pte(switcher_pages[0],
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
-
- /* The only other thing we map is this CPU's pair of pages. */
- i = 1 + cpu*2;
-
- /* First page (Guest registers) is writable from the Guest */
- set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_pages[i]),
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)));
-
- /*
- * The second page contains the "struct lguest_ro_state", and is
- * read-only.
- */
- set_pte(&pte[i+1], pfn_pte(page_to_pfn(switcher_pages[i+1]),
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
-}
-
/*
* We've made it through the page table code. Perhaps our tired brains are
* still processing the details, or perhaps we're simply glad it's over.
@@ -1163,29 +1141,3 @@
*
* There is just one file remaining in the Host.
*/
-
-/*H:510
- * At boot or module load time, init_pagetables() allocates and populates
- * the Switcher PTE page for each CPU.
- */
-__init int init_pagetables(struct page **switcher_pages)
-{
- unsigned int i;
-
- for_each_possible_cpu(i) {
- switcher_pte_page(i) = (pte_t *)get_zeroed_page(GFP_KERNEL);
- if (!switcher_pte_page(i)) {
- free_switcher_pte_pages();
- return -ENOMEM;
- }
- populate_switcher_pte_page(i, switcher_pages);
- }
- return 0;
-}
-/*:*/
-
-/* Cleaning up simply involves freeing the PTE page for each CPU. */
-void free_pagetables(void)
-{
- free_switcher_pte_pages();
-}