xen: fix allocation and use of large ldts

When the ldt gets to more than 1 page in size, the kernel uses vmalloc to allocate it. This means that:
- when making the ldt RO, we must update the pages in both the vmalloc mapping and the linear mapping to make sure there are no RW aliases.
- we need to use arbitrary_virt_to_machine to compute the machine addr for each update

---
arch/x86/xen/enlighten.c | 49 ++++++++++++++++++++++++++++++++++++----------

1 file changed, 39 insertions(+), 10 deletions(-)

===================================================================

@@ -305,24 +305,53 @@

	return 0;
}

+/* If 'v' is a vmalloc mapping, then find the linear mapping of the
+ page (if any) and also set its protections to match. */
+static void set_aliased_prot(void *v, pgprot_t prot)
+{
+ int level;
+ pte_t *ptep;
+ pte_t pte;
+ unsigned long pfn;
+ struct page *page;
+
+ ptep = lookup_address((unsigned long)v, &level);
+ BUG_ON(ptep == NULL);
+
+ pfn = pte_pfn(*ptep);
+ page = pfn_to_page(pfn);
+
+ pte = pfn_pte(pfn, prot);
+
+ if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
+ BUG();
+
+ if (!PageHighMem(page)) {
+ void *av = __va(PFN_PHYS(pfn));
+
+ if (av != v)
+ if (HYPERVISOR_update_va_mapping((unsigned long)av, pte, 0))
+ BUG();
+ } else
+ kmap_flush_unused();
+}
+
static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries) {
- unsigned pages = roundup(entries * LDT_ENTRY_SIZE, PAGE_SIZE);
- void *v = ldt;

+	const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
	int i;

- for(i = 0; i < pages; i += PAGE_SIZE)
- make_lowmem_page_readonly(v + i);
+ for(i = 0; i < entries; i += entries_per_page)
+ set_aliased_prot(ldt + i, PAGE_KERNEL_RO);
}

static void xen_free_ldt(struct desc_struct *ldt, unsigned entries) {
- unsigned pages = roundup(entries * LDT_ENTRY_SIZE, PAGE_SIZE);
- void *v = ldt;

+	const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
	int i;

- for(i = 0; i < pages; i += PAGE_SIZE)
- make_lowmem_page_readwrite(v + i);
+ for(i = 0; i < entries; i += entries_per_page)
+ set_aliased_prot(ldt + i, PAGE_KERNEL);
}

static void xen_set_ldt(const void *addr, unsigned entries) @@ -426,7 +455,7 @@
const void *ptr)

{
	unsigned long lp = (unsigned long)&dt[entrynum];
-	xmaddr_t mach_lp = virt_to_machine(lp);
+	xmaddr_t mach_lp = arbitrary_virt_to_machine(lp);
	u64 entry = *(u64 *)ptr;

	preempt_disable();

@@ -559,7 +588,7 @@
}

static void xen_load_sp0(struct tss_struct *tss,
- struct thread_struct *thread)
+ struct thread_struct *thread)

{
	struct multicall_space mcs = xen_mc_entry(0);
	MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->sp0);

applied to tip/x86/xen, thanks Jeremy.

Ingo

Thanks. Here's a follow-up tidy patch.

Subject: xen: tidy up ldt fixes

Add a proper comment for set_aliased_prot() and fix an unsigned long/void * warning.

---
arch/x86/xen/enlighten.c | 9 +++++----

1 file changed, 5 insertions(+), 4 deletions(-)

===================================================================

@@ -395,8 +395,10 @@

}

/*
- * If 'v' is a vmalloc mapping, then find the linear mapping of the
- * page (if any) and also set its protections to match:
+ * Set the page permissions for a particular virtual address. If the
+ * address is a vmalloc mapping (or other non-linear mapping), then
+ * find the linear mapping of the page and also set its protections to
+ * match.
*/
static void set_aliased_prot(void *v, pgprot_t prot)
{
@@ -545,8 +547,7 @@
static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
const void *ptr)
{
- unsigned long lp = (unsigned long)&dt[entrynum];
- xmaddr_t mach_lp = arbitrary_virt_to_machine(lp);

+	xmaddr_t mach_lp = arbitrary_virt_to_machine(&dt[entrynum]);
	u64 entry = *(u64 *)ptr;

	preempt_disable();

applied to tip/x86/xen - thanks Jeremy.

Ingo