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Message-ID: <20200617162800.05a12502@oasis.local.home>
Date: Wed, 17 Jun 2020 16:28:00 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Oscar Carter <oscar.carter@....com>
Cc: Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/trace: Remove function callback casts
On Mon, 15 Jun 2020 16:22:45 -0400
Steven Rostedt <rostedt@...dmis.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
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