[PATCH v7 15/17] tracing: make ftrace for MIPS more robust

Wu Zhangjin
2009-11-09T15:33:38Z

Seems there is no failure meet when working with the C source code to
load/hijack the text & stack space, but we must ensure our source code
is robust enough, This patch does it via adding extra exception
handling.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
---
arch/mips/include/asm/ftrace.h | 57 ++++++++++++++++++++++++++++++++++++++++
arch/mips/kernel/ftrace.c | 46 +++++++++++++++++++++++---------
2 files changed, 90 insertions(+), 13 deletions(-)

diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
index aa7c80b..f78d763 100644
--- a/arch/mips/include/asm/ftrace.h
+++ b/arch/mips/include/asm/ftrace.h
@@ -19,6 +19,62 @@
extern void _mcount(void);
#define mcount _mcount

+#define safe_load(load, src, dst, error) \
+do { \
+ asm volatile ( \
+ "1: " load " %[" STR(dst) "], 0(%[" STR(src) "])\n"\
+ " li %[" STR(error) "], 0\n" \
+ "2:\n" \
+ \
+ ".section .fixup, \"ax\"\n" \
+ "3: li %[" STR(error) "], 1\n" \
+ " j 2b\n" \
+ ".previous\n" \
+ \
+ ".section\t__ex_table,\"a\"\n\t" \
+ STR(PTR) "\t1b, 3b\n\t" \
+ ".previous\n" \
+ \
+ : [dst] "=&r" (dst), [error] "=r" (error)\
+ : [src] "r" (src) \
+ : "memory" \
+ ); \
+} while (0)
+
+#define safe_store(store, src, dst, error) \
+do { \
+ asm volatile ( \
+ "1: " store " %[" STR(src) "], 0(%[" STR(dst) "])\n"\
+ " li %[" STR(error) "], 0\n" \
+ "2:\n" \
+ \
+ ".section .fixup, \"ax\"\n" \
+ "3: li %[" STR(error) "], 1\n" \
+ " j 2b\n" \
+ ".previous\n" \
+ \
+ ".section\t__ex_table,\"a\"\n\t"\
+ STR(PTR) "\t1b, 3b\n\t" \
+ ".previous\n" \
+ \
+ : [error] "=r" (error) \
+ : [dst] "r" (dst), [src] "r" (src)\
+ : "memory" \
+ ); \
+} while (0)
+
+#define safe_load_code(dst, src, error) \
+ safe_load(STR(lw), src, dst, error)
+#define safe_store_code(src, dst, error) \
+ safe_store(STR(sw), src, dst, error)
+
+#define safe_load_stack(dst, src, error) \
+ safe_load(STR(PTR_L), src, dst, error)
+
+#define safe_store_stack(src, dst, error) \
+ safe_store(STR(PTR_S), src, dst, error)
+
+
#ifdef CONFIG_DYNAMIC_FTRACE
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
@@ -27,6 +83,7 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)

struct dyn_arch_ftrace {
};
+
#endif /* CONFIG_DYNAMIC_FTRACE */

/* not trace the timecounter_read* in kernel/time/clocksource.c */
diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index af3ceed..a4e25b8 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -31,7 +31,13 @@ static unsigned int ftrace_nop = 0x00000000;

static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
{
- *(unsigned int *)ip = new_code;
+ int faulted;
+
+ /* *(unsigned int *)ip = new_code; */
+ safe_store_code(new_code, ip, faulted);
+
+ if (unlikely(faulted))
+ return -EFAULT;

flush_icache_range(ip, ip + 8);

@@ -124,6 +130,7 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
{
unsigned long sp, ip, ra;
unsigned int code;
+ int faulted;

/* move to the instruction "lui v1, HI_16BIT_OF_MCOUNT" */
ip = self_addr - 20;
@@ -133,8 +140,11 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
do {
ip -= 4;

- /* get the code at "ip" */
- code = *(unsigned int *)ip;
+ /* get the code at "ip": code = *(unsigned int *)ip; */
+ safe_load_code(code, ip, faulted);
+
+ if (unlikely(faulted))
+ return 0;

/* If we hit the non-store instruction before finding where the
* ra is stored, then this is a leaf function and it does not
@@ -145,11 +155,14 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
} while (((code & S_RA_SP) != S_RA_SP));

sp = fp + (code & OFFSET_MASK);
- ra = *(unsigned long *)sp;
+
+ /* ra = *(unsigned long *)sp; */
+ safe_load_stack(ra, sp, faulted);
+ if (unlikely(faulted))
+ return 0;

if (ra == parent)
return sp;
-
return 0;
}

@@ -164,6 +177,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
struct ftrace_graph_ent trace;
unsigned long return_hooker = (unsigned long)
&return_to_handler;
+ int faulted;

if (unlikely(atomic_read(&current->tracing_graph_pause)))
return;
@@ -177,21 +191,23 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
* ftrace_get_parent_addr() does it!
*/

- old = *parent;
+ /* old = *parent; */
+ safe_load_stack(old, parent, faulted);
+ if (unlikely(faulted))
+ goto out;

parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old,
(unsigned long)parent,
fp);
-
/* If fails when getting the stack address of the non-leaf function's
* ra, stop function graph tracer and return */
- if (parent == 0) {
- ftrace_graph_stop();
- WARN_ON(1);
- return;
- }
+ if (parent == 0)
+ goto out;

- *parent = return_hooker;
+ /* *parent = return_hooker; */
+ safe_store_stack(return_hooker, parent, faulted);
+ if (unlikely(faulted))
+ goto out;

if (ftrace_push_return_trace(old, self_addr, &trace.depth, fp) ==
-EBUSY) {
@@ -206,5 +222,9 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
current->curr_ret_stack--;
*parent = old;
}
+ return;
+out:
+ ftrace_graph_stop();
+ WARN_ON(1);
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
--
1.6.2.1