On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keesc...@chromium.org> wrote: > +/* > + * Build "write rarely" infrastructure for flipping memory r/w > + * on a per-CPU basis. > + */ > +#ifndef CONFIG_HAVE_ARCH_RARE_WRITE > +# define __wr_rare > +# define __wr_rare_type > +# define __rare_write(__var, __val) (__var = (__val)) > +# define rare_write_begin() do { } while (0) > +# define rare_write_end() do { } while (0) > +#else > +# define __wr_rare __ro_after_init > +# define __wr_rare_type const > +# ifdef CONFIG_HAVE_ARCH_RARE_WRITE_MEMCPY > +# define __rare_write_n(dst, src, len) ({ \ > + BUILD_BUG(!builtin_const(len)); \ > + __arch_rare_write_memcpy((dst), (src), (len)); \ > + }) > +# define __rare_write(var, val) __rare_write_n(&(var), &(val), sizeof(var)) > +# else > +# define __rare_write(var, val) ((*(typeof((typeof(var))0) *)&(var)) = > (val)) > +# endif > +# define rare_write_begin() __arch_rare_write_begin() > +# define rare_write_end() __arch_rare_write_end() > +#endif > +#define rare_write(__var, __val) ({ \ > + rare_write_begin(); \ > + __rare_write(__var, __val); \ > + rare_write_end(); \ > + __var; \ > +}) > +
Of course, only after sending this do I realize that the MEMCPY case will need to be further adjusted, since it currently can't take literals. I guess something like this needs to be done: #define __rare_write(var, val) ({ \ typeof(var) __src = (val); \ __rare_write_n(&(var), &(__src), sizeof(var)); \ }) -Kees -- Kees Cook Pixel Security