[RFC v2][PATCH 01/11] Introduce rare_write() infrastructure
From: Kees Cook <hidden>
Date: 2017-03-29 18:24:01
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On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook [off-list ref] wrote:
quoted hunk ↗ jump to hunk
+/* + * 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