From: Geert Uytterhoeven <ge...@linux-m68k.org> Date: Tue, 5 Dec 2017 21:20:57 +0100
> Hi Tobin, > > On Wed, Nov 29, 2017 at 3:05 AM, Tobin C. Harding <m...@tobin.cc> wrote: >> Currently there exist approximately 14 000 places in the kernel where >> addresses are being printed using an unadorned %p. This potentially >> leaks sensitive information regarding the Kernel layout in memory. Many >> of these calls are stale, instead of fixing every call lets hash the >> address by default before printing. This will of course break some >> users, forcing code printing needed addresses to be updated. >> >> Code that _really_ needs the address will soon be able to use the new >> printk specifier %px to print the address. > >> --- a/lib/vsprintf.c >> +++ b/lib/vsprintf.c > >> +/* Maps a pointer to a 32 bit unique identifier. */ >> +static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec >> spec) >> +{ >> + unsigned long hashval; >> + const int default_width = 2 * sizeof(ptr); >> + >> + if (unlikely(!have_filled_random_ptr_key)) { >> + spec.field_width = default_width; >> + /* string length must be less than default_width */ >> + return string(buf, end, "(ptrval)", spec); >> + } >> + >> +#ifdef CONFIG_64BIT >> + hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key); >> + /* >> + * Mask off the first 32 bits, this makes explicit that we have >> + * modified the address (and 32 bits is plenty for a unique ID). >> + */ >> + hashval = hashval & 0xffffffff; >> +#else >> + hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key); >> +#endif > > Would it make sense to keep the 3 lowest bits of the address? > > Currently printed pointers no longer have any correlation with the actual > alignment in memory of the object, which is a typical cause of a class of > bugs. Yeah, this is driving people nuts who wonder why pointers are aligned all weird now.