@@ -100,6 +100,16 @@ endif
export quiet Q KBUILD_VERBOSE
+# Disallow use of trace_printk. Can be used by production kernels.
+ifeq ("$(origin DISALLOW_TRACE_PRINTK)", "command line")
+ KBUILD_DISALLOW_TRACE_PRINTK = $(DISALLOW_TRACE_PRINTK)
+endif
+ifndef KBUILD_DISALLOW_TRACE_PRINTK
+ KBUILD_DISALLOW_TRACE_PRINTK = 0
+endif
+
+export KBUILD_DISALLOW_TRACE_PRINTK
+
# Kbuild will save output files in the current working directory.
# This does not need to match to the root of the kernel source tree.
#
@@ -846,6 +856,10 @@ endif # CONFIG_DEBUG_INFO
KBUILD_CFLAGS += $(DEBUG_CFLAGS)
export DEBUG_CFLAGS
+ifeq ($(KBUILD_DISALLOW_TRACE_PRINTK),1)
+KBUILD_CFLAGS += -DDISALLOW_TRACE_PRINTK
+endif
+
ifdef CONFIG_FUNCTION_TRACER
ifdef CONFIG_FTRACE_MCOUNT_RECORD
# gcc 5 supports generating the mcount tables directly
@@ -688,6 +688,12 @@ do { \
____trace_printk_check_format(fmt, ##args); \
} while (0)
+#ifdef DISALLOW_TRACE_PRINTK
+#define ALLOW_TRACE_PRINTK 0
+#else
+#define ALLOW_TRACE_PRINTK 1
+#endif
+
/**
* trace_printk - printf formatting in the ftrace buffer
* @fmt: the printf format for printing
@@ -721,10 +727,13 @@ do { \
#define trace_printk(fmt, ...) \
do { \
char _______STR[] = __stringify((__VA_ARGS__)); \
+ \
+ static_assert(ALLOW_TRACE_PRINTK, "trace_printk called."); \
+ \
if (sizeof(_______STR) > 3) \
do_trace_printk(fmt, ##__VA_ARGS__); \
else \
- trace_puts(fmt); \
+ do_trace_puts(fmt); \
} while (0)
#define do_trace_printk(fmt, args...) \
@@ -773,6 +782,11 @@ int __trace_printk(unsigned long ip, const char *fmt, ...);
*/
#define trace_puts(str) ({ \
+ static_assert(ALLOW_TRACE_PRINTK, "trace_puts called."); \
+ do_trace_puts(str); \
+})
+
+#define do_trace_puts(str) ({ \
static const char *trace_printk_fmt __used \
__attribute__((section("__trace_printk_fmt"))) = \
__builtin_constant_p(str) ? str : NULL; \
@@ -794,6 +808,7 @@ extern void trace_dump_stack(int skip);
*/
#define ftrace_vprintk(fmt, vargs) \
do { \
+ static_assert(ALLOW_TRACE_PRINTK, "ftrace_vprintk called."); \
if (__builtin_constant_p(fmt)) { \
static const char *trace_printk_fmt __used \
__attribute__((section("__trace_printk_fmt"))) = \
trace_printk is meant as a debugging tool, and should not be compiled into production code without specific debug Kconfig options enabled, or source code changes, as indicated by the warning that shows up on boot if any trace_printk is called: ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE ** ** ** ** trace_printk() being used. Allocating extra memory. ** ** ** ** This means that this is a DEBUG kernel and it is ** ** unsafe for production use. ** If DISALLOW_TRACE_PRINTK=1 is passed on the make command line, the kernel will generate a build-time error if trace_printk is used. We expect distributors to set this option for their production kernels. Note that the code to handle trace_printk is still present, so this does not prevent people from compiling out-of-tree kernel modules, or BPF programs. Also, we are not making this a kernel config option as we want the developer convenience of being able to reuse a production kernel config, add trace_printk for debugging, and rebuild, without any config changes. Signed-off-by: Nicolas Boichat <drinkcat@chromium.org> --- Changes since v5: - Rebased, no functional change (moved the Makefile change a little lower to keep all the DEBUG stuff together). Changes since v4: - Turns this into a make option, instead of a config option, as suggested by Steven Rostedt <rostedt@goodmis.org>. Changes since v2/v3: - Rebase only, v3 didn't exist as I just split out the other necessary patches. - Added patch 3/3 to fix atomisp_compat_css20.c Changes since v1: - Use static_assert instead of __static_assert (Jason Gunthorpe) - Fix issues that can be detected by this patch (running some randconfig in a loop, kernel test robot, or manual inspection), by: - Making some debug config options that use trace_printk depend on the new config option. - Adding 3 patches before this one. There is a question from Alexei whether the warning is warranted, and it's possibly too strongly worded, but the fact is, we do not want trace_printk to be sprinkled in kernel code by default, unless a very specific Kconfig command is enabled (or preprocessor macro). There's at least 3 reasons that I can come up with: 1. trace_printk introduces some overhead. 2. If the kernel keeps adding always-enabled trace_printk, it will be much harder for developers to make use of trace_printk for debugging. 3. People may assume that trace_printk is for debugging only, and may accidentally output sensitive data (theoritical at this stage). Makefile | 14 ++++++++++++++ include/linux/kernel.h | 17 ++++++++++++++++- 2 files changed, 30 insertions(+), 1 deletion(-)