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Date: Thu, 30 Mar 2017 16:44:02 +0900
From: Ho-Eun Ryu <hoeun.ryu@...il.com>
To: Kees Cook <keescook@...omium.org>
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 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
> -Kees
>
> --
> Kees Cook
> Pixel Security
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