[uml-devel] Implement vsyscall/sysenter, patch 2/4

[bodo.stroesser@fujitsu-siemens.com]

To make the vsyscall-page available for copy_from_user() and
ptrace(), we should use kernel's "gate-vma" mechanism.
Therefore we need a valid page structure. To have this, one
page (or more) is allocated at boot time, the contents of the
vsyscall-page is copied into this page and the page's pte is
inserted in swapper's pagetables.
Now it will be copied into the pagetables of all processes.

Note: this alone doesn't work, since FIXADDR_USER_START and
      FIXADDR_USER_END are not yet defined correctly. Also
      access_ok_skas() does not yet grant read accesses to
      pages not in the normal user area.

Risks:
Please check the first hunk! I don't know, whether this change is OK.
Maybe fixrange_init() is wrong anyway with 3-level-pagetables?


Signed-off-by: Bodo Stroesser <bodo.stroesser@fujitsu-siemens.com>

---


--- linux-2.6.9-rc2-orig/arch/um/kernel/mem.c	2004-09-27 19:24:56.000000000 +0200
+++ linux-2.6.9-rc2/arch/um/kernel/mem.c	2004-10-05 15:36:57.032218318 +0200
@@ -121,7 +121,7 @@
 
 	for ( ; (i < PTRS_PER_PGD) && (vaddr < end); pgd++, i++) {
 		pmd = (pmd_t *)pgd;
-		for (; (j < PTRS_PER_PMD) && (vaddr != end); pmd++, j++) {
+		for (; (j < PTRS_PER_PMD) && (vaddr < end); pmd++, j++) {
 			if (pmd_none(*pmd)) {
 				pte = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
 				set_pmd(pmd, __pmd(_KERNPG_TABLE + 
@@ -175,6 +175,29 @@
 }
 #endif /* CONFIG_HIGHMEM */
 
+static void __init fixaddr_user_init( void)
+{
+	long size = FIXADDR_USER_END - FIXADDR_USER_START;
+	pgd_t *pgd;
+	pmd_t *pmd;
+	pte_t *pte;
+	unsigned long paddr, vaddr = FIXADDR_USER_START;
+
+	if (  ! size )
+		return;
+
+	fixrange_init( FIXADDR_USER_START, FIXADDR_USER_END, swapper_pg_dir);
+	paddr = (unsigned long)alloc_bootmem_low_pages( size);
+	memcpy( (void *)paddr, (void *)FIXADDR_USER_START, size);
+	paddr = __pa(paddr);
+	for ( ; size > 0; size-=PAGE_SIZE, vaddr+=PAGE_SIZE, paddr+=PAGE_SIZE) {
+		pgd = swapper_pg_dir + pgd_index(vaddr);
+		pmd = pmd_offset(pgd, vaddr);
+		pte = pte_offset_kernel(pmd, vaddr);
+		pte_set_val( (*pte), paddr, PAGE_READONLY);
+	}
+}
+
 void paging_init(void)
 {
 	unsigned long zones_size[MAX_NR_ZONES], vaddr;
@@ -195,6 +218,8 @@
 	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
 	fixrange_init(vaddr, FIXADDR_TOP, swapper_pg_dir);
 
+	fixaddr_user_init();
+
 #ifdef CONFIG_HIGHMEM
 	init_highmem();
 #endif


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