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* [PATCH] tracing: Use linker magic instead of recasting ftrace_ops_list_func()
@ 2020-06-17 20:56 Steven Rostedt
  2020-06-17 21:30   ` Jann Horn
                   ` (2 more replies)
  0 siblings, 3 replies; 11+ messages in thread
From: Steven Rostedt @ 2020-06-17 20:56 UTC (permalink / raw)
  To: LKML
  Cc: Ingo Molnar, Kees Cook, kernel-hardening, Oscar Carter, Andrew Morton

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

In an effort to enable -Wcast-function-type in the top-level Makefile to
support Control Flow Integrity builds, all function casts need to be
removed.

This means that ftrace_ops_list_func() can no longer be defined as
ftrace_ops_no_ops(). The reason for ftrace_ops_no_ops() is to use that when
an architecture calls ftrace_ops_list_func() with only two parameters
(called from assembly). And to make sure there's no C side-effects, those
archs call ftrace_ops_no_ops() which only has two parameters, as
ftrace_ops_list_func() has four parameters.

Instead of a typecast, use vmlinux.lds.h to define ftrace_ops_list_func() to
arch_ftrace_ops_list_func() that will define the proper set of parameters.

Link: https://lore.kernel.org/r/20200614070154.6039-1-oscar.carter@gmx.com

Requested-by: Oscar Carter <oscar.carter@gmx.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/asm-generic/vmlinux.lds.h |  7 ++++++-
 kernel/trace/ftrace.c             | 23 ++++++++++-------------
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index db600ef218d7..120babd9ba44 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -145,13 +145,18 @@
  * Need to also make ftrace_stub_graph point to ftrace_stub
  * so that the same stub location may have different protocols
  * and not mess up with C verifiers.
+ *
+ * ftrace_ops_list_func will be defined as arch_ftrace_ops_list_func
+ * as some archs will have a different prototype for that function
+ * but ftrace_ops_list_func() will have a single prototype.
  */
 #define MCOUNT_REC()	. = ALIGN(8);				\
 			__start_mcount_loc = .;			\
 			KEEP(*(__mcount_loc))			\
 			KEEP(*(__patchable_function_entries))	\
 			__stop_mcount_loc = .;			\
-			ftrace_stub_graph = ftrace_stub;
+			ftrace_stub_graph = ftrace_stub;	\
+			ftrace_ops_list_func = arch_ftrace_ops_list_func;
 #else
 # ifdef CONFIG_FUNCTION_TRACER
 #  define MCOUNT_REC()	ftrace_stub_graph = ftrace_stub;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f060838e9cbb..b775d399026e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -119,14 +119,9 @@ struct ftrace_ops __rcu *ftrace_ops_list __read_mostly = &ftrace_list_end;
 ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
 struct ftrace_ops global_ops;
 
-#if ARCH_SUPPORTS_FTRACE_OPS
-static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
-				 struct ftrace_ops *op, struct pt_regs *regs);
-#else
-/* See comment below, where ftrace_ops_list_func is defined */
-static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
-#define ftrace_ops_list_func ((ftrace_func_t)ftrace_ops_no_ops)
-#endif
+/* Defined by vmlinux.lds.h see the commment above arch_ftrace_ops_list_func for details */
+void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
+			  struct ftrace_ops *op, struct pt_regs *regs);
 
 static inline void ftrace_ops_init(struct ftrace_ops *ops)
 {
@@ -6859,21 +6854,23 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
  * Note, CONFIG_DYNAMIC_FTRACE_WITH_REGS expects a full regs to be saved.
  * An architecture can pass partial regs with ftrace_ops and still
  * set the ARCH_SUPPORTS_FTRACE_OPS.
+ *
+ * In vmlinux.lds.h, ftrace_ops_list_func() is defined to be
+ * arch_ftrace_ops_list_func.
  */
 #if ARCH_SUPPORTS_FTRACE_OPS
-static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
-				 struct ftrace_ops *op, struct pt_regs *regs)
+void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
+			       struct ftrace_ops *op, struct pt_regs *regs)
 {
 	__ftrace_ops_list_func(ip, parent_ip, NULL, regs);
 }
-NOKPROBE_SYMBOL(ftrace_ops_list_func);
 #else
-static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip)
+void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
 {
 	__ftrace_ops_list_func(ip, parent_ip, NULL, NULL);
 }
-NOKPROBE_SYMBOL(ftrace_ops_no_ops);
 #endif
+NOKPROBE_SYMBOL(arch_ftrace_ops_list_func);
 
 /*
  * If there's only one function registered but it does not support
-- 
2.25.4


^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2020-06-18 17:59 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-06-17 20:56 [PATCH] tracing: Use linker magic instead of recasting ftrace_ops_list_func() Steven Rostedt
2020-06-17 21:30 ` Jann Horn
2020-06-17 21:30   ` Jann Horn
2020-06-17 22:36   ` Steven Rostedt
2020-06-17 23:12     ` Jann Horn
2020-06-17 23:12       ` Jann Horn
2020-06-18 16:41       ` Steven Rostedt
2020-06-18 17:58         ` Jann Horn
2020-06-18 17:58           ` Jann Horn
2020-06-18  9:13 ` kernel test robot
2020-06-18 10:06 ` kernel test robot

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