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Date: Thu, 14 Feb 2019 12:28:49 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Igor Stoppa <igor.stoppa@...il.com>
Cc: Igor Stoppa <igor.stoppa@...wei.com>,
Andy Lutomirski <luto@...capital.net>,
Nadav Amit <nadav.amit@...il.com>,
Matthew Wilcox <willy@...radead.org>,
Kees Cook <keescook@...omium.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
Ahmed Soliman <ahmedsoliman@...a.vt.edu>,
linux-integrity@...r.kernel.org,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v5 03/12] __wr_after_init: Core and default arch
On Thu, Feb 14, 2019 at 12:41:32AM +0200, Igor Stoppa wrote:
> +static inline void *wr_memset(void *p, int c, __kernel_size_t n)
> +{
> + return memset(p, c, n);
> +}
> +
> +static inline void *wr_memcpy(void *p, const void *q, __kernel_size_t n)
> +{
> + return memcpy(p, q, n);
> +}
> +
> +#define wr_assign(var, val) ((var) = (val))
> +#define wr_rcu_assign_pointer(p, v) rcu_assign_pointer(p, v)
> +
> +#else
> +
> +void *wr_memset(void *p, int c, __kernel_size_t n);
> +void *wr_memcpy(void *p, const void *q, __kernel_size_t n);
> +
> +/**
> + * wr_assign() - sets a write-rare variable to a specified value
> + * @var: the variable to set
> + * @val: the new value
> + *
> + * Returns: the variable
> + */
> +
> +#define wr_assign(dst, val) ({ \
> + typeof(dst) tmp = (typeof(dst))val; \
> + \
> + wr_memcpy(&dst, &tmp, sizeof(dst)); \
> + dst; \
> +})
> +
> +/**
> + * wr_rcu_assign_pointer() - initialize a pointer in rcu mode
> + * @p: the rcu pointer - it MUST be aligned to a machine word
> + * @v: the new value
> + *
> + * Returns the value assigned to the rcu pointer.
> + *
> + * It is provided as macro, to match rcu_assign_pointer()
> + * The rcu_assign_pointer() is implemented as equivalent of:
> + *
> + * smp_mb();
> + * WRITE_ONCE();
> + */
> +#define wr_rcu_assign_pointer(p, v) ({ \
> + smp_mb(); \
> + wr_assign(p, v); \
> + p; \
> +})
This requires that wr_memcpy() (through wr_assign) is single-copy-atomic
for native types. There is not a comment in sight that states this.
Also, is this true of x86/arm64 memcpy ?
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