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Date: Wed, 29 Mar 2017 11:23:57 -0700
From: Kees Cook <keescook@...omium.org>
To: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Cc: Kees Cook <keescook@...omium.org>, Mark Rutland <mark.rutland@....com>,
Andy Lutomirski <luto@...nel.org>, Hoeun Ryu <hoeun.ryu@...il.com>, PaX Team <pageexec@...email.hu>,
Emese Revfy <re.emese@...il.com>, Russell King <linux@...linux.org.uk>,
"x86@...nel.org" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure
On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@...omium.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
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