scs: Add page accounting for shadow call stack allocations

This change adds accounting for the memory allocated for shadow stacks.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

drivers/base/node.c

@@ -415,6 +415,9 @@ static ssize_t node_read_meminfo(struct device *dev,
 		       "Node %d AnonPages:      %8lu kB\n"
 		       "Node %d Shmem:          %8lu kB\n"
 		       "Node %d KernelStack:    %8lu kB\n"
+#ifdef CONFIG_SHADOW_CALL_STACK
+		       "Node %d ShadowCallStack:%8lu kB\n"
+#endif
 		       "Node %d PageTables:     %8lu kB\n"
 		       "Node %d NFS_Unstable:   %8lu kB\n"
 		       "Node %d Bounce:         %8lu kB\n"
@@ -438,6 +441,9 @@ static ssize_t node_read_meminfo(struct device *dev,
 		       nid, K(node_page_state(pgdat, NR_ANON_MAPPED)),
 		       nid, K(i.sharedram),
 		       nid, sum_zone_node_page_state(nid, NR_KERNEL_STACK_KB),
+#ifdef CONFIG_SHADOW_CALL_STACK
+		       nid, sum_zone_node_page_state(nid, NR_KERNEL_SCS_KB),
+#endif
 		       nid, K(sum_zone_node_page_state(nid, NR_PAGETABLE)),
 		       nid, K(node_page_state(pgdat, NR_UNSTABLE_NFS)),
 		       nid, K(sum_zone_node_page_state(nid, NR_BOUNCE)),

fs/proc/meminfo.c

@@ -103,6 +103,10 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 	show_val_kb(m, "SUnreclaim:     ", sunreclaim);
 	seq_printf(m, "KernelStack:    %8lu kB\n",
 		   global_zone_page_state(NR_KERNEL_STACK_KB));
+#ifdef CONFIG_SHADOW_CALL_STACK
+	seq_printf(m, "ShadowCallStack:%8lu kB\n",
+		   global_zone_page_state(NR_KERNEL_SCS_KB));
+#endif
 	show_val_kb(m, "PageTables:     ",
 		    global_zone_page_state(NR_PAGETABLE));
 

include/linux/mmzone.h

@@ -156,6 +156,9 @@ enum zone_stat_item {
 	NR_MLOCK,		/* mlock()ed pages found and moved off LRU */
 	NR_PAGETABLE,		/* used for pagetables */
 	NR_KERNEL_STACK_KB,	/* measured in KiB */
+#if IS_ENABLED(CONFIG_SHADOW_CALL_STACK)
+	NR_KERNEL_SCS_KB,	/* measured in KiB */
+#endif
 	/* Second 128 byte cacheline */
 	NR_BOUNCE,
 #if IS_ENABLED(CONFIG_ZSMALLOC)

kernel/scs.c

@@ -6,8 +6,10 @@
  */
 
 #include <linux/kasan.h>
+#include <linux/mm.h>
 #include <linux/scs.h>
 #include <linux/slab.h>
+#include <linux/vmstat.h>
 #include <asm/scs.h>
 
 static struct kmem_cache *scs_cache;
@@ -40,6 +42,17 @@ void __init scs_init(void)
 	scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, 0, 0, NULL);
 }
 
+static struct page *__scs_page(struct task_struct *tsk)
+{
+	return virt_to_page(task_scs(tsk));
+}
+
+static void scs_account(struct task_struct *tsk, int account)
+{
+	mod_zone_page_state(page_zone(__scs_page(tsk)), NR_KERNEL_SCS_KB,
+		account * (SCS_SIZE / 1024));
+}
+
 int scs_prepare(struct task_struct *tsk, int node)
 {
 	void *s = scs_alloc(node);
@@ -49,6 +62,7 @@ int scs_prepare(struct task_struct *tsk, int node)
 
 	task_scs(tsk) = s;
 	task_scs_offset(tsk) = 0;
+	scs_account(tsk, 1);
 
 	return 0;
 }
@@ -61,5 +75,6 @@ void scs_release(struct task_struct *tsk)
 		return;
 
 	WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
+	scs_account(tsk, -1);
 	scs_free(s);
 }

mm/page_alloc.c

@@ -5411,6 +5411,9 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 			" managed:%lukB"
 			" mlocked:%lukB"
 			" kernel_stack:%lukB"
+#ifdef CONFIG_SHADOW_CALL_STACK
+			" shadow_call_stack:%lukB"
+#endif
 			" pagetables:%lukB"
 			" bounce:%lukB"
 			" free_pcp:%lukB"
@@ -5433,6 +5436,9 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 			K(zone_managed_pages(zone)),
 			K(zone_page_state(zone, NR_MLOCK)),
 			zone_page_state(zone, NR_KERNEL_STACK_KB),
+#ifdef CONFIG_SHADOW_CALL_STACK
+			zone_page_state(zone, NR_KERNEL_SCS_KB),
+#endif
 			K(zone_page_state(zone, NR_PAGETABLE)),
 			K(zone_page_state(zone, NR_BOUNCE)),
 			K(free_pcp),

mm/vmstat.c

@@ -1119,6 +1119,9 @@ const char * const vmstat_text[] = {
 	"nr_mlock",
 	"nr_page_table_pages",
 	"nr_kernel_stack",
+#if IS_ENABLED(CONFIG_SHADOW_CALL_STACK)
+	"nr_shadow_call_stack",
+#endif
 	"nr_bounce",
 #if IS_ENABLED(CONFIG_ZSMALLOC)
 	"nr_zspages",