Subject: [PATCHv2 1/4] arm64: Add CONFIG_DEBUG_SET_MODULE_RONX support

From: [email-masked] (Will Deacon)
Date: Tue, 3 Jun 2014 16:22:01 +0100

Hi Laura,

This is looking better, but comments inline.

On Mon, Jun 02, 2014 at 09:57:35PM +0100, Laura Abbott wrote:
> 
> In a similar fashion to other architecture, add the infrastructure
> and Kconfig to enable DEBUG_SET_MODULE_RONX support. When
> enabled, module ranges will be marked read-only/no-execute as
> appropriate.
> 
> Signed-off-by: Laura Abbott <[email-masked]>
> ---
>  arch/arm64/Kconfig.debug            |  11 ++++
>  arch/arm64/include/asm/cacheflush.h |   4 ++
>  arch/arm64/mm/Makefile              |   2 +-
>  arch/arm64/mm/pageattr.c            | 121 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 137 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/mm/pageattr.c

[...]

>  obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> new file mode 100644
> index 0000000..d8ab747
> --- /dev/null
> +++ b/arch/arm64/mm/pageattr.c
> @@ -0,0 +1,121 @@
> +/*
> + * Copyright (c) 2014, The Linux Foundation. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 and
> + * only version 2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +#include <linux/sched.h>
> +
> +#include <asm/pgtable.h>
> +#include <asm/tlbflush.h>
> +
> +static pte_t clear_pte_bit(pte_t pte, pgprot_t prot)
> +{
> +	pte_val(pte) &= ~pgprot_val(prot);
> +	return pte;
> +}
> +
> +static pte_t set_pte_bit(pte_t pte, pgprot_t prot)
> +{
> +	pte_val(pte) |= pgprot_val(prot);
> +	return pte;
> +}

We could actually re-use these for building our pte_mk* functions in
pgtable.h. Care to move them there?

> +static int __change_memory(pte_t *ptep, pgtable_t token, unsigned long addr,
> +			pgprot_t prot, bool set)
> +{
> +	pte_t pte;
> +
> +	if (set)
> +		pte = set_pte_bit(*ptep, prot);
> +	else
> +		pte = clear_pte_bit(*ptep, prot);
> +	set_pte(ptep, pte);
> +	return 0;
> +}
> +
> +static int set_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
> +			void *data)
> +{
> +	pgprot_t prot = (pgprot_t)data;
> +
> +	return __change_memory(ptep, token, addr, prot, true);
> +}
> +
> +static int clear_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
> +			void *data)
> +{
> +	pgprot_t prot = (pgprot_t)data;
> +
> +	return __change_memory(ptep, token, addr, prot, false);
> +}
> +
> +static int change_memory_common(unsigned long addr, int numpages,
> +				pgprot_t prot, bool set)
> +{
> +	unsigned long start = addr;
> +	unsigned long size = PAGE_SIZE*numpages;
> +	unsigned long end = start + size;
> +	int ret;
> +
> +	if (start < MODULES_VADDR || start >= MODULES_END)
> +		return -EINVAL;
> +
> +	if (end < MODULES_VADDR || end >= MODULES_END)
> +		return -EINVAL;

Can you use is_module_address here, or do you need to change the page
attributes for areas where no modules are currently loaded too?

> +	if (set)
> +		ret = apply_to_page_range(&init_mm, start, size,
> +					set_page_range, (void *)prot);
> +	else
> +		ret = apply_to_page_range(&init_mm, start, size,
> +					clear_page_range, (void *)prot);
> +
> +	flush_tlb_kernel_range(start, end);
> +	isb();
> +	return ret;

We already have an isb in flush_tlb_kernel_range.

> +static int change_memory_set_bit(unsigned long addr, int numpages,
> +					pgprot_t prot)
> +{
> +	return change_memory_common(addr, numpages, prot, true);
> +}
> +
> +static int change_memory_clear_bit(unsigned long addr, int numpages,
> +					pgprot_t prot)
> +{
> +	return change_memory_common(addr, numpages, prot, false);
> +}
> +
> +int set_memory_ro(unsigned long addr, int numpages)
> +{
> +	return change_memory_set_bit(addr, numpages, __pgprot(PTE_RDONLY));
> +}
> +EXPORT_SYMBOL_GPL(set_memory_ro);
> +
> +int set_memory_rw(unsigned long addr, int numpages)
> +{
> +	return change_memory_clear_bit(addr, numpages, __pgprot(PTE_RDONLY));
> +}
> +EXPORT_SYMBOL_GPL(set_memory_rw);

I'm slightly worried about the interaction with this and PTE_WRITE (see
linux-next). If the kernel pages are marked as PTE_DIRTY | PTE_WRITE, then
setting read-only is a weird contradiction. Can you take PTE_WRITE into
account for these two please?

Will