[PATCH] Add the canary field to the PDA area and the task struct

This patch adds the per thread cookie field to the task struct and the PDA.
Also it makes sure that the PDA value gets the new cookie value at context
switch, and that a new task gets a new cookie at task creation time.
Signed-off-by: Arjan van Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andi Kleen <ak@suse.de>
CC: Andi Kleen <ak@suse.de>

arch/x86_64/kernel/process.c

@@ -625,6 +625,14 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	unlazy_fpu(prev_p);
 	write_pda(kernelstack,
 		  task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);
+#ifdef CONFIG_CC_STACKPROTECTOR
+	write_pda(stack_canary, next_p->stack_canary);
+	/*
+	 * Build time only check to make sure the stack_canary is at
+	 * offset 40 in the pda; this is a gcc ABI requirement
+	 */
+	BUILD_BUG_ON(offsetof(struct x8664_pda, stack_canary) != 40);
+#endif
 
 	/*
 	 * Now maybe reload the debug registers and handle I/O bitmaps

include/asm-x86_64/pda.h

@@ -16,7 +16,12 @@ struct x8664_pda {
 	unsigned long oldrsp; 	    /* 24 user rsp for system call */
         int irqcount;		    /* 32 Irq nesting counter. Starts with -1 */
 	int cpunumber;		    /* 36 Logical CPU number */
-	char *irqstackptr;	/* 40 top of irqstack */
+#ifdef CONFIG_CC_STACKPROTECTOR
+	unsigned long stack_canary;	/* 40 stack canary value */
+					/* gcc-ABI: this canary MUST be at
+					   offset 40!!! */
+#endif
+	char *irqstackptr;
 	int nodenumber;		    /* number of current node */
 	unsigned int __softirq_pending;
 	unsigned int __nmi_count;	/* number of NMI on this CPUs */

include/linux/sched.h

@@ -819,6 +819,11 @@ struct task_struct {
 	unsigned did_exec:1;
 	pid_t pid;
 	pid_t tgid;
+
+#ifdef CONFIG_CC_STACKPROTECTOR
+	/* Canary value for the -fstack-protector gcc feature */
+	unsigned long stack_canary;
+#endif
 	/* 
 	 * pointers to (original) parent process, youngest child, younger sibling,
 	 * older sibling, respectively.  (p->father can be replaced with 

kernel/fork.c

@@ -45,6 +45,7 @@
 #include <linux/cn_proc.h>
 #include <linux/delayacct.h>
 #include <linux/taskstats_kern.h>
+#include <linux/random.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -175,6 +176,10 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
 	tsk->thread_info = ti;
 	setup_thread_stack(tsk, orig);
 
+#ifdef CONFIG_CC_STACKPROTECTOR
+	tsk->stack_canary = get_random_int();
+#endif
+
 	/* One for us, one for whoever does the "release_task()" (usually parent) */
 	atomic_set(&tsk->usage,2);
 	atomic_set(&tsk->fs_excl, 0);