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From: Kees Cook <keescook@chromium.org>
To: Ho-Eun Ryu <hoeun.ryu@gmail.com>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Andy Lutomirski <luto@kernel.org>,
	PaX Team <pageexec@freemail.hu>, Emese Revfy <re.emese@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	"x86@kernel.org" <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure
Date: Thu, 30 Mar 2017 10:02:55 -0700
Message-ID: <CAGXu5j+ym33s=nUqmpViR0UJrHo6Bu7+LxsMtvKgvpOzhYxXkw@mail.gmail.com> (raw)
In-Reply-To: <466B31B4-0535-44EE-B0F0-F758A79A7B4F@gmail.com>

On Thu, Mar 30, 2017 at 12:44 AM, Ho-Eun Ryu <hoeun.ryu@gmail.com> wrote:
>
>> On 30 Mar 2017, at 3:23 AM, Kees Cook <keescook@chromium.org> wrote:
>>
>> On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@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)); \
>> })
>>
>
> Right, and it has a problem with BUILD_BUG, which causes compilation error when CONFIG_HABE_ARCH_RARE_WRITE_MEMCPY is true
> BUILD_BUG is defined in <linux/bug.h> but <linux/bug.h> includes <linux/compiler.h>
>
> Please see the following.
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 3334fa9..3fa50e1 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -350,11 +350,11 @@ static __always_inline void __write_once_size(volatile vo\
> id *p, void *res, int s
>  # 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_n(var, val, len)        ({                                 \
> +               typeof(val) __val = val;                                                    \
> +               __arch_rare_write_memcpy(&(var), &(__val), (len));      \
>         })
> -#  define __rare_write(var, val)  __rare_write_n(&(var), &(val), sizeof(var))
> +#  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

Thanks for the catch, I'll update this (I'll use compiletime_assert,
which is defined in compiler.h).

-Kees

-- 
Kees Cook
Pixel Security

  reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-29 18:15 [RFC v2] " Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 01/11] " Kees Cook
2017-03-29 18:23   ` Kees Cook
2017-03-30  7:44     ` Ho-Eun Ryu
2017-03-30 17:02       ` Kees Cook [this message]
2017-04-07  8:09   ` Ho-Eun Ryu
2017-04-07 20:38     ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 02/11] lkdtm: add test for " Kees Cook
2017-03-30  9:34   ` [kernel-hardening] " Ian Campbell
2017-03-30 16:16     ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 03/11] net: switch sock_diag handlers to rare_write() Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook
2017-03-29 22:38   ` Andy Lutomirski
2017-03-30  1:41     ` Kees Cook
2017-04-05 23:57       ` Andy Lutomirski
2017-04-06  0:14         ` Kees Cook
2017-04-06 15:59           ` Andy Lutomirski
2017-04-07  8:34             ` [kernel-hardening] " Mathias Krause
2017-04-07  9:46               ` Thomas Gleixner
2017-04-07 10:51                 ` Mathias Krause
2017-04-07 13:14                   ` Thomas Gleixner
2017-04-07 13:30                     ` Mathias Krause
2017-04-07 16:14                       ` Andy Lutomirski
2017-04-07 16:22                         ` Mark Rutland
2017-04-07 19:58                         ` PaX Team
2017-04-08  4:58                           ` Andy Lutomirski
2017-04-09 12:47                             ` PaX Team
2017-04-10  0:10                               ` Andy Lutomirski
2017-04-10 10:42                                 ` PaX Team
2017-04-10 16:01                                   ` Andy Lutomirski
2017-04-07 20:44                         ` Thomas Gleixner
2017-04-07 21:20                           ` Kees Cook
2017-04-08  4:12                             ` Daniel Micay
2017-04-08  4:13                               ` Daniel Micay
2017-04-08  4:21                         ` Daniel Micay
2017-04-08  5:07                           ` Andy Lutomirski
2017-04-08  7:33                             ` Daniel Micay
2017-04-08 15:20                               ` Andy Lutomirski
2017-04-09 10:53                                 ` Ingo Molnar
2017-04-10 10:22                                 ` Mark Rutland
2017-04-09 20:24                             ` PaX Team
2017-04-10  0:31                               ` Andy Lutomirski
2017-04-10 19:47                                 ` PaX Team
2017-04-10 20:27                                   ` Andy Lutomirski
2017-04-10 20:13                               ` Kees Cook
2017-04-10 20:17                                 ` Andy Lutomirski
2017-04-07 19:25                       ` Thomas Gleixner
2017-04-07 14:45                   ` Peter Zijlstra
2017-04-10 10:29                     ` Mark Rutland
2017-04-07 19:52                 ` PaX Team
2017-04-10  8:26                   ` Thomas Gleixner
2017-04-10 19:55                     ` PaX Team
2017-04-07  9:37   ` Peter Zijlstra
2017-03-29 18:15 ` [RFC v2][PATCH 05/11] ARM: mm: dump: Add domain to output Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 06/11] ARM: domains: Extract common USER domain init Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 07/11] ARM: mm: set DOMAIN_WR_RARE for rodata Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 08/11] ARM: Implement __arch_rare_write_begin/end() Kees Cook
2017-04-07  9:36   ` Peter Zijlstra
2017-03-29 18:16 ` [RFC v2][PATCH 09/11] list: add rare_write() list helpers Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 10/11] gcc-plugins: Add constify plugin Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 11/11] cgroups: force all struct cftype const Kees Cook
2017-03-29 19:00 ` [RFC v2] Introduce rare_write() infrastructure Russell King - ARM Linux
2017-03-29 19:14   ` Kees Cook

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