[PATCH 4/9] pstore/ftrace: Add recursion protection to the ftrace callback

Steven Rostedt
2020-10-29T00:57:28Z

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.

The default for ftrace_ops is going to assume recursion protection unless
otherwise specified.

Cc: Thomas Meyer <thomas@m3y3r.de>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
fs/pstore/ftrace.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
index 5c0450701293..816210fc5d3a 100644
--- a/fs/pstore/ftrace.c
+++ b/fs/pstore/ftrace.c
@@ -28,6 +28,7 @@ static void notrace pstore_ftrace_call(unsigned long ip,
struct ftrace_ops *op,
struct pt_regs *regs)
{
+ int bit;
unsigned long flags;
struct pstore_ftrace_record rec = {};
struct pstore_record record = {
@@ -40,6 +41,10 @@ static void notrace pstore_ftrace_call(unsigned long ip,
if (unlikely(oops_in_progress))
return;

+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
+
local_irq_save(flags);

rec.ip = ip;
@@ -49,6 +54,7 @@ static void notrace pstore_ftrace_call(unsigned long ip,
psinfo->write(&record);

local_irq_restore(flags);
+ ftrace_test_recursion_unlock(bit);
}

static struct ftrace_ops pstore_ftrace_ops __read_mostly = {
--
2.28.0