s390/stackstrace: Detect vdso stack frames

Clear the backchain of the extra stack frame added by the vdso user wrapper
code. This allows the user stack walker to detect and skip the non-standard
stack frame. Without this an incorrect instruction pointer would be added
to stack traces, and stack frame walking would be continued with a more or
less random back chain.

Fixes: aa44433a ("s390: add USER_STACKTRACE support")
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/include/asm/processor.h

@@ -98,6 +98,7 @@ void cpu_detect_mhz_feature(void);
 
 extern const struct seq_operations cpuinfo_op;
 extern void execve_tail(void);
+unsigned long vdso_text_size(void);
 unsigned long vdso_size(void);
 
 /*

arch/s390/kernel/asm-offsets.c

@@ -66,6 +66,7 @@ int main(void)
 	OFFSET(__SF_SIE_CONTROL_PHYS, stack_frame, sie_control_block_phys);
 	DEFINE(STACK_FRAME_OVERHEAD, sizeof(struct stack_frame));
 	BLANK();
+	OFFSET(__SFUSER_BACKCHAIN, stack_frame_user, back_chain);
 	DEFINE(STACK_FRAME_USER_OVERHEAD, sizeof(struct stack_frame_user));
 	OFFSET(__SFVDSO_RETURN_ADDRESS, stack_frame_vdso_wrapper, return_address);
 	DEFINE(STACK_FRAME_VDSO_OVERHEAD, sizeof(struct stack_frame_vdso_wrapper));

arch/s390/kernel/stacktrace.c

@@ -92,10 +92,16 @@ static inline bool ip_invalid(unsigned long ip)
 	return false;
 }
 
+static inline bool ip_within_vdso(unsigned long ip)
+{
+	return in_range(ip, current->mm->context.vdso_base, vdso_text_size());
+}
+
 void arch_stack_walk_user_common(stack_trace_consume_fn consume_entry, void *cookie,
 				 struct perf_callchain_entry_ctx *entry,
 				 const struct pt_regs *regs, bool perf)
 {
+	struct stack_frame_vdso_wrapper __user *sf_vdso;
 	struct stack_frame_user __user *sf;
 	unsigned long ip, sp;
 	bool first = true;
@@ -112,11 +118,25 @@ void arch_stack_walk_user_common(stack_trace_consume_fn consume_entry, void *coo
 	while (1) {
 		if (__get_user(sp, &sf->back_chain))
 			break;
+		/*
+		 * VDSO entry code has a non-standard stack frame layout.
+		 * See VDSO user wrapper code for details.
+		 */
+		if (!sp && ip_within_vdso(ip)) {
+			sf_vdso = (void __user *)sf;
+			if (__get_user(ip, &sf_vdso->return_address))
+				break;
+			sp = (unsigned long)sf + STACK_FRAME_VDSO_OVERHEAD;
+			sf = (void __user *)sp;
+			if (__get_user(sp, &sf->back_chain))
+				break;
+		} else {
+			sf = (void __user *)sp;
+			if (__get_user(ip, &sf->gprs[8]))
+				break;
+		}
 		/* Sanity check: ABI requires SP to be 8 byte aligned. */
-		if (!sp || sp & 0x7)
-			break;
-		sf = (void __user *)sp;
-		if (__get_user(ip, &sf->gprs[8]))
+		if (sp & 0x7)
 			break;
 		if (ip_invalid(ip)) {
 			/*

arch/s390/kernel/vdso.c

@@ -210,17 +210,22 @@ static unsigned long vdso_addr(unsigned long start, unsigned long len)
 	return addr;
 }
 
-unsigned long vdso_size(void)
+unsigned long vdso_text_size(void)
 {
-	unsigned long size = VVAR_NR_PAGES * PAGE_SIZE;
+	unsigned long size;
 
 	if (is_compat_task())
-		size += vdso32_end - vdso32_start;
+		size = vdso32_end - vdso32_start;
 	else
-		size += vdso64_end - vdso64_start;
+		size = vdso64_end - vdso64_start;
 	return PAGE_ALIGN(size);
 }
 
+unsigned long vdso_size(void)
+{
+	return vdso_text_size() + VVAR_NR_PAGES * PAGE_SIZE;
+}
+
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	unsigned long addr = VDSO_BASE;

arch/s390/kernel/vdso64/vdso_user_wrapper.S

@@ -23,6 +23,7 @@ __kernel_\func:
 	CFI_VAL_OFFSET 15,-STACK_FRAME_USER_OVERHEAD
 	stg	%r14,__SFVDSO_RETURN_ADDRESS(%r15)
 	CFI_REL_OFFSET 14,__SFVDSO_RETURN_ADDRESS
+	xc	__SFUSER_BACKCHAIN(8,%r15),__SFUSER_BACKCHAIN(%r15)
 	brasl	%r14,__s390_vdso_\func
 	lg	%r14,__SFVDSO_RETURN_ADDRESS(%r15)
 	CFI_RESTORE 14