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From: Steven Rostedt <rostedt@goodmis.org>
To: Oscar Carter <oscar.carter@gmx.com>
Cc: Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@redhat.com>,
	kernel-hardening@lists.openwall.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel/trace: Remove function callback casts
Date: Wed, 17 Jun 2020 16:28:00 -0400	[thread overview]
Message-ID: <20200617162800.05a12502@oasis.local.home> (raw)
In-Reply-To: <20200615162245.13d3feff@oasis.local.home>

On Mon, 15 Jun 2020 16:22:45 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> As I was saying. This typecast is being paranoid, as archs will call
> the ftrace_ops_list_func directly, and only pass in two parameters.
> 
> Now one way around this is to instead of having the typecast, I could
> use linker magic to create another function that I can define without
> the typecast to get the same effect. Similar to what I did in commit:
> 
> 46f9469247c6f ("ftrace: Rename ftrace_graph_stub to ftrace_stub_graph")

Would something like this work for you?

-- Steve

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

  reply	other threads:[~2020-06-17 20:28 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-14  7:01 [PATCH] kernel/trace: Remove function callback casts Oscar Carter
2020-06-15 20:17 ` Steven Rostedt
2020-06-15 20:22   ` Steven Rostedt
2020-06-17 20:28     ` Steven Rostedt [this message]
2020-06-20 14:23       ` Oscar Carter

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