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Message-ID: <20181221184120.GG10600@bombadil.infradead.org>
Date: Fri, 21 Dec 2018 10:41:20 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Igor Stoppa <igor.stoppa@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>,
Peter Zijlstra <peterz@...radead.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
igor.stoppa@...wei.com, Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>,
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: [PATCH 03/12] __wr_after_init: generic functionality
On Fri, Dec 21, 2018 at 08:14:14PM +0200, Igor Stoppa wrote:
> +static inline int memtst(void *p, int c, __kernel_size_t len)
I don't understand why you're verifying that writes actually happen
in production code. Sure, write lib/test_wrmem.c or something, but
verifying every single rare write seems like a mistake to me.
> +#ifndef CONFIG_PRMEM
So is this PRMEM or wr_mem? It's not obvious that CONFIG_PRMEM controls
wrmem.
> +#define wr_assign(var, val) ((var) = (val))
The hamming distance between 'var' and 'val' is too small. The convention
in the line immediately below (p and v) is much more readable.
> +#define wr_rcu_assign_pointer(p, v) rcu_assign_pointer(p, v)
> +#define wr_assign(var, val) ({ \
> + typeof(var) tmp = (typeof(var))val; \
> + \
> + wr_memcpy(&var, &tmp, sizeof(var)); \
> + var; \
> +})
Doesn't wr_memcpy return 'var' anyway?
> +/**
> + * wr_memcpy() - copyes size bytes from q to p
typo
> + * @p: beginning of the memory to write to
> + * @q: beginning of the memory to read from
> + * @size: amount of bytes to copy
> + *
> + * Returns pointer to the destination
> + * The architecture code must provide:
> + * void __wr_enable(wr_state_t *state)
> + * void *__wr_addr(void *addr)
> + * void *__wr_memcpy(void *p, const void *q, __kernel_size_t size)
> + * void __wr_disable(wr_state_t *state)
This section shouldn't be in the user documentation of wr_memcpy().
> + */
> +void *wr_memcpy(void *p, const void *q, __kernel_size_t size)
> +{
> + wr_state_t wr_state;
> + void *wr_poking_addr = __wr_addr(p);
> +
> + if (WARN_ONCE(!wr_ready, "No writable mapping available") ||
Surely not. If somebody's called wr_memcpy() before wr_ready is set,
that means we can just call memcpy().
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