Re: [PATCHv2 2/2] arm64: Allow changing of attributes outside of modules

[zhong jiang]

On 2015/11/12 19:55, zhong jiang wrote:
> On 2015/11/11 9:57, Laura Abbott wrote:
>> Currently, the set_memory_* functions that are implemented for arm64
>> are restricted to module addresses only. This was mostly done
>> because arm64 maps normal zone memory with larger page sizes to
>> improve TLB performance. This has the side effect though of making it
>> difficult to adjust attributes at the PAGE_SIZE granularity. There are
>> an increasing number of use cases related to security where it is
>> necessary to change the attributes of kernel memory. Add functionality
>> to the page attribute changing code under a Kconfig to let systems
>> designers decide if they want to make the trade off of security for TLB
>> pressure.
>>
>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
>> ---
>> v2: Re-worked to account for the full range of addresses. Will also just
>> update the section blocks instead of splitting if the addresses are aligned
>> properly.
>> ---
>>  arch/arm64/Kconfig       |  12 ++++
>>  arch/arm64/mm/mm.h       |   3 +
>>  arch/arm64/mm/mmu.c      |   2 +-
>>  arch/arm64/mm/pageattr.c | 174 +++++++++++++++++++++++++++++++++++++++++------
>>  4 files changed, 170 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 851fe11..46725e8 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -521,6 +521,18 @@ config ARCH_HAS_CACHE_LINE_SIZE
>>  
>>  source "mm/Kconfig"
>>  
>> +config DEBUG_CHANGE_PAGEATTR
>> +	bool "Allow all kernel memory to have attributes changed"
>> +	default y
>> +	help
>> +	  If this option is selected, APIs that change page attributes
>> +	  (RW <-> RO, X <-> NX) will be valid for all memory mapped in
>> +	  the kernel space. The trade off is that there may be increased
>> +	  TLB pressure from finer grained page mapping. Turn on this option
>> +	  if security is more important than performance
>> +
>> +	  If in doubt, say Y
>> +
>>  config SECCOMP
>>  	bool "Enable seccomp to safely compute untrusted bytecode"
>>  	---help---
>> diff --git a/arch/arm64/mm/mm.h b/arch/arm64/mm/mm.h
>> index ef47d99..7b0dcc4 100644
>> --- a/arch/arm64/mm/mm.h
>> +++ b/arch/arm64/mm/mm.h
>> @@ -1,3 +1,6 @@
>>  extern void __init bootmem_init(void);
>>  
>>  void fixup_init(void);
>> +
>> +void split_pud(pud_t *old_pud, pmd_t *pmd);
>> +void split_pmd(pmd_t *pmd, pte_t *pte);
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 496c3fd..9353e3c 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -73,7 +73,7 @@ static void __init *early_alloc(unsigned long sz)
>>  /*
>>   * remap a PMD into pages
>>   */
>> -static void split_pmd(pmd_t *pmd, pte_t *pte)
>> +void split_pmd(pmd_t *pmd, pte_t *pte)
>>  {
>>  	unsigned long pfn = pmd_pfn(*pmd);
>>  	unsigned long addr = pfn << PAGE_SHIFT;
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index 3571c73..4a95fed 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -15,25 +15,162 @@
>>  #include <linux/module.h>
>>  #include <linux/sched.h>
>>  
>> +#include <asm/pgalloc.h>
>>  #include <asm/pgtable.h>
>>  #include <asm/tlbflush.h>
>>  
>> -struct page_change_data {
>> -	pgprot_t set_mask;
>> -	pgprot_t clear_mask;
>> -};
>> +#include "mm.h"
>>  
>> -static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
>> -			void *data)
>> +static int update_pte_range(struct mm_struct *mm, pmd_t *pmd,
>> +				unsigned long addr, unsigned long end,
>> +				pgprot_t clear, pgprot_t set)
>>  {
>> -	struct page_change_data *cdata = data;
>> -	pte_t pte = *ptep;
>> +	pte_t *pte;
>> +	int err = 0;
>> +
>> +	if (pmd_sect(*pmd)) {
>> +		if (!IS_ENABLED(CONFIG_DEBUG_CHANGE_PAGEATTR)) {
>> +			err = -EINVAL;
>> +			goto out;
>> +		}
>> +		pte = pte_alloc_one_kernel(&init_mm, addr);
>> +		if (!pte) {
>> +			err = -ENOMEM;
>> +			goto out;
>> +		}
>> +		split_pmd(pmd, pte);
>> +		__pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
>> +	}
>> +
>> +
>> +	pte = pte_offset_kernel(pmd, addr);
>> +	if (pte_none(*pte)) {
>> +		err = -EFAULT;
>> +		goto out;
>> +	}
>> +
>> +	do {
>> +		pte_t p = *pte;
>> +
>> +		p = clear_pte_bit(p, clear);
>> +		p = set_pte_bit(p, set);
>> +		set_pte(pte, p);
>> +
>> +	} while (pte++, addr += PAGE_SIZE, addr != end);
>> +
>> +out:
>> +	return err;
>> +}
>> +
>> +
>> +static int update_pmd_range(struct mm_struct *mm, pud_t *pud,
>> +				unsigned long addr, unsigned long end,
>> +				pgprot_t clear, pgprot_t set)
>> +{
>> +	pmd_t *pmd;
>> +	unsigned long next;
>> +	int err = 0;
>> +
>> +	if (pud_sect(*pud)) {
>> +		if (!IS_ENABLED(CONFIG_DEBUG_CHANGE_PAGEATTR)) {
>> +			err = -EINVAL;
>> +			goto out;
>> +		}
>> +		pmd = pmd_alloc_one(&init_mm, addr);
>> +		if (!pmd) {
>> +			err = -ENOMEM;
>> +			goto out;
>> +		}
>> +		split_pud(pud, pmd);
>> +		pud_populate(&init_mm, pud, pmd);
>> +	}
>> +
>>  
>> -	pte = clear_pte_bit(pte, cdata->clear_mask);
>> -	pte = set_pte_bit(pte, cdata->set_mask);
>> +	pmd = pmd_offset(pud, addr);
>> +	if (pmd_none(*pmd)) {
>> +		err = -EFAULT;
>> +		goto out;
>> +	}
>> +
> 
> we try to preserve the section area, but the addr | end does not ensure that
> physical memory is alignment. In addtion, if numpages cross section area, and
> addr points to the physical memory is alignment to the section. In this case,
> we should consider to retain the section.
> 
>> +	do {
>> +		next = pmd_addr_end(addr, end);
>> +		if (((addr | end) & ~SECTION_MASK) == 0) {
>> +			unsigned long paddr = pmd_pfn(*pmd) << PAGE_SHIFT;
>> +			pgprot_t prot = __pgprot((pmd_val(*pmd) ^ paddr));
>> +
>> +			pgprot_val(prot) &= ~pgprot_val(clear);
>> +			pgprot_val(prot) |= pgprot_val(set);
>> +			set_pmd(pmd, __pmd(paddr | pgprot_val(prot)));
>> +		} else {
>> +			err = update_pte_range(mm, pmd, addr, next, clear, set);
>> +		}
>> +		if (err)
>> +			break;
>> +	} while (pmd++, addr = next, addr != end);
>> +out:
>> +	return err;
>> +}
>> +
>> +
>> +static int update_pud_range(struct mm_struct *mm, pgd_t *pgd,
>> +					unsigned long addr, unsigned long end,
>> +					pgprot_t clear, pgprot_t set)
>> +{
>> +	pud_t *pud;
>> +	unsigned long next;
>> +	int err = 0;
>> +
>> +	pud = pud_offset(pgd, addr);
>> +	if (pud_none(*pud)) {
>> +		err = -EFAULT;
>> +		goto out;
>> +	}
>>  
>> -	set_pte(ptep, pte);
>> -	return 0;
>> +	do {
>> +		next = pud_addr_end(addr, end);
>> +		if (pud_sect(*pud) && ((addr | next) & ~PUD_MASK) == 0) {
>> +			unsigned long paddr = pud_pfn(*pud) << PAGE_SHIFT;
>> +			pgprot_t prot = __pgprot(pud_val(*pud) ^ paddr);
>> +
>> +			pgprot_val(prot) &= ~pgprot_val(clear);
>> +			pgprot_val(prot) |= pgprot_val(set);
>> +			set_pud(pud, __pud(paddr | pgprot_val(prot)));
>> +		} else {
>> +			err = update_pmd_range(mm, pud, addr, next, clear, set);
>> +		}
>> +		if (err)
>> +			break;
>> +	} while (pud++, addr = next, addr != end);
>> +
>> +out:
>> +	return err;
>> +}
>> +
>> +static int update_page_range(unsigned long addr,
>> +				unsigned long end, pgprot_t clear,
>> +				pgprot_t set)
>> +{
>> +	pgd_t *pgd;
>> +	unsigned long next;
>> +	int err;
>> +	struct mm_struct *mm = &init_mm;
>> +
>> +	BUG_ON(addr >= end);
>> +	pgd = pgd_offset(mm, addr);
>> +	if (pgd_none(*pgd)) {
>> +		err = -EFAULT;
>> +		goto out;
>> +	}
>> +
>> +	do {
>> +		next = pgd_addr_end(addr, end);
>> +		err = update_pud_range(mm, pgd, addr, next, clear, set);
>> +		if (err)
>> +			break;
>> +	} while (pgd++, addr = next, addr != end);
>> +
>> +out:
>> +	return err;
>>  }
>>  
>>  static int change_memory_common(unsigned long addr, int numpages,
>> @@ -43,7 +180,6 @@ static int change_memory_common(unsigned long addr, int numpages,
>>  	unsigned long size = PAGE_SIZE*numpages;
>>  	unsigned long end = start + size;
>>  	int ret;
>> -	struct page_change_data data;
>>  
>>  	if (!PAGE_ALIGNED(addr)) {
>>  		start &= PAGE_MASK;
>> @@ -51,17 +187,15 @@ static int change_memory_common(unsigned long addr, int numpages,
>>  		WARN_ON_ONCE(1);
>>  	}
>>  
>> -	if (start < MODULES_VADDR || start >= MODULES_END)
>> +	if (start < PAGE_OFFSET && !is_vmalloc_addr((void *)start) &&
>> +		(start < MODULES_VADDR || start >= MODULES_END))
>>  		return -EINVAL;
>>  
>> -	if (end < MODULES_VADDR || end >= MODULES_END)
>> +	if (end < PAGE_OFFSET && !is_vmalloc_addr((void *)end) &&
>> +		(end < MODULES_VADDR || end >= MODULES_END))
>>  		return -EINVAL;
>>  
>> -	data.set_mask = set_mask;
>> -	data.clear_mask = clear_mask;
>> -
>> -	ret = apply_to_page_range(&init_mm, start, size, change_page_range,
>> -					&data);
>> +	ret = update_page_range(addr, end, clear_mask, set_mask);
>>  
>>  	flush_tlb_kernel_range(start, end);
>>  	return ret;
> 
> 
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> .
> 

Hi Laura

In change_memory_common, why the address is  so restricted ?


Thanks
zhongjiang


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