While debugging an issue I needed to see if the pointers were being processed correctly with trace_printk() and after using "%p" and triggering my bug and trace output, I was disappointed that all my pointers were random garbage and didn't produce anything useful for me. I had to rewrite all the trace_printk()s to use "%lx" instead.
As trace_printk() is not to be used for anything but debugging, and this is enforced by printing in the dmesg: ********************************************************** ** 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 you see this message and you are not debugging ** ** the kernel, report this immediately to your vendor! ** ** ** ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE ** ********************************************************** on boot up if trace_printk() is used (or when a module is loaded that uses trace_printk()), we can safely assume that the use of trace_printk() is not going to be accidentally added to production code (and if it is, they should be whacked with an overcooked spaghetti noodle). A new bool is added called "trace_debug" and if it is set, then %p will not be hashed. Both trace_debug is set and kptr_restrict is set to zero in the same code that produces the above banner. This will allow trace_printk() to not be affected by security code, as trace_printk() should never be run on a machine that needs security of this kind. Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> --- diff --git a/include/linux/printk.h b/include/linux/printk.h index e9b603ee9953..7ef6c31d874a 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -278,6 +278,7 @@ static inline void printk_safe_flush_on_panic(void) #endif extern int kptr_restrict; +extern bool trace_debug; extern asmlinkage void dump_stack(void) __cold; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0f47e653ffd8..cb58cd4ee3a7 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2864,6 +2864,10 @@ void trace_printk_init_buffers(void) buffers_allocated = 1; + /* This is a debug kernel, allow pointers to be shown */ + trace_debug = true; + kptr_restrict = 0; + /* * trace_printk_init_buffers() can be called by modules. * If that happens, then we need to start cmdline recording diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 89f8a4a4b770..425644ceedcb 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1345,6 +1345,7 @@ char *uuid_string(char *buf, char *end, const u8 *addr, } int kptr_restrict __read_mostly; +bool trace_debug __read_mostly; static noinline_for_stack char *restricted_pointer(char *buf, char *end, const void *ptr, @@ -1962,6 +1963,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, return pointer_string(buf, end, ptr, spec); } + /* When the kernel is in debugging mode, show all pointers */ + if (trace_debug) + return restricted_pointer(buf, end, ptr, spec); + /* default is to _not_ leak addresses, hash before printing */ return ptr_to_id(buf, end, ptr, spec); }