[IA64] prevent accidental modification of args in jprobe handler

When jprobe is hit, the function parameters of the original function
should be saved before jprobe handler is executed, and restored it after
jprobe handler is executed, because jprobe handler might change the
register values due to tail call optimization by the gcc.

Signed-off-by: Zhang Yanmin <[e-mail]>
Signed-off-by: Anil S Keshavamurthy <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

arch/ia64/kernel/jprobes.S

···
 GLOBAL_ENTRY(jprobe_inst_return)
 	br.call.sptk.many b0=jprobe_break
 END(jprobe_inst_return)
+
+GLOBAL_ENTRY(invalidate_stacked_regs)
+	movl r16=invalidate_restore_cfm
+	;;
+	mov b6=r16
+	;;
+	br.ret.sptk.many b6
+	;;
+invalidate_restore_cfm:
+	mov r16=ar.rsc
+	;;
+	mov ar.rsc=r0
+	;;
+	loadrs
+	;;
+	mov ar.rsc=r16
+	;;
+	br.cond.sptk.many rp
+END(invalidate_stacked_regs)
+
+GLOBAL_ENTRY(flush_register_stack)
+	// flush dirty regs to backing store (must be first in insn group)
+	flushrs
+	;;
+	br.ret.sptk.many rp
+END(flush_register_stack)
+

arch/ia64/kernel/kprobes.c

···
 	return ret;
 }
 
+struct param_bsp_cfm {
+	unsigned long ip;
+	unsigned long *bsp;
+	unsigned long cfm;
+};
+
+static void ia64_get_bsp_cfm(struct unw_frame_info *info, void *arg)
+{
+	unsigned long ip;
+	struct param_bsp_cfm *lp = arg;
+
+	do {
+		unw_get_ip(info, &ip);
+		if (ip == 0)
+			break;
+		if (ip == lp->ip) {
+			unw_get_bsp(info, (unsigned long*)&lp->bsp);
+			unw_get_cfm(info, (unsigned long*)&lp->cfm);
+			return;
+		}
+	} while (unw_unwind(info) >= 0);
+	lp->bsp = 0;
+	lp->cfm = 0;
+	return;
+}
+
 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 {
 	struct jprobe *jp = container_of(p, struct jprobe, kp);
 	unsigned long addr = ((struct fnptr *)(jp->entry))->ip;
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	struct param_bsp_cfm pa;
+	int bytes;
+
+	/*
+	 * Callee owns the argument space and could overwrite it, eg
+	 * tail call optimization. So to be absolutely safe
+	 * we save the argument space before transfering the control
+	 * to instrumented jprobe function which runs in
+	 * the process context
+	 */
+	pa.ip = regs->cr_iip;
+	unw_init_running(ia64_get_bsp_cfm, &pa);
+	bytes = (char *)ia64_rse_skip_regs(pa.bsp, pa.cfm & 0x3f)
+				- (char *)pa.bsp;
+	memcpy( kcb->jprobes_saved_stacked_regs,
+		pa.bsp,
+		bytes );
+	kcb->bsp = pa.bsp;
+	kcb->cfm = pa.cfm;
 
 	/* save architectural state */
 	kcb->jprobe_saved_regs = *regs;
···
 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	int bytes;
 
+	/* restoring architectural state */
 	*regs = kcb->jprobe_saved_regs;
+
+	/* restoring the original argument space */
+	flush_register_stack();
+	bytes = (char *)ia64_rse_skip_regs(kcb->bsp, kcb->cfm & 0x3f)
+				- (char *)kcb->bsp;
+	memcpy( kcb->bsp,
+		kcb->jprobes_saved_stacked_regs,
+		bytes );
+	invalidate_stacked_regs();
+
 	preempt_enable_no_resched();
 	return 1;
 }

include/asm-ia64/kprobes.h

···
 	unsigned long status;
 };
 
+#define	MAX_PARAM_RSE_SIZE	(0x60+0x60/0x3f)
 /* per-cpu kprobe control block */
 struct kprobe_ctlblk {
 	unsigned long kprobe_status;
 	struct pt_regs jprobe_saved_regs;
+	unsigned long jprobes_saved_stacked_regs[MAX_PARAM_RSE_SIZE];
+	unsigned long *bsp;
+	unsigned long cfm;
 	struct prev_kprobe prev_kprobe;
 };
 
···
 static inline void jprobe_return(void)
 {
 }
+extern void invalidate_stacked_regs(void);
+extern void flush_register_stack(void);
 
 #endif				/* _ASM_KPROBES_H */