[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAGXu5j+ym33s=nUqmpViR0UJrHo6Bu7+LxsMtvKgvpOzhYxXkw@mail.gmail.com>
Date: Thu, 30 Mar 2017 10:02:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Ho-Eun Ryu <hoeun.ryu@...il.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Mark Rutland <mark.rutland@....com>, Andy Lutomirski <luto@...nel.org>, 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 Thu, Mar 30, 2017 at 12:44 AM, Ho-Eun Ryu <hoeun.ryu@...il.com> wrote:
>
>> On 30 Mar 2017, at 3:23 AM, Kees Cook <keescook@...omium.org> wrote:
>>
>> 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)); \
>> })
>>
>
> 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
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
