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

zhong jiang
2015-11-04T03:18:05Z

On 2015/11/4 5:48, 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@fedoraproject.org>
> ---
> arch/arm64/Kconfig.debug | 11 +++++++
> arch/arm64/mm/mm.h | 3 ++
> arch/arm64/mm/mmu.c | 2 +-
> arch/arm64/mm/pageattr.c | 74 ++++++++++++++++++++++++++++++++++++++++++++----
> 4 files changed, 84 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index d6285ef..abc6922 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -89,6 +89,17 @@ config DEBUG_ALIGN_RODATA
>
> If in doubt, say N
>
> +config DEBUG_CHANGE_PAGEATTR
> + bool "Allow all kernel memory to have attributes changed"
> + 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 performance is more important than security
> +
> + If in doubt, say N
> +
> source "drivers/hwtracing/coresight/Kconfig"
>
> endmenu
> 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 ff41efa..cefad2d 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -72,7 +72,7 @@ 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 e47ed1c..48a4ce9 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -15,9 +15,12 @@
> #include <linux/module.h>
> #include <linux/sched.h>
>
> +#include <asm/pgalloc.h>
> #include <asm/pgtable.h>
> #include <asm/tlbflush.h>
>
> +#include "mm.h"
> +
> struct page_change_data {
> pgprot_t set_mask;
> pgprot_t clear_mask;
> @@ -36,6 +39,66 @@ static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
> return 0;
> }
>
> +#ifdef CONFIG_DEBUG_CHANGE_PAGEATTR
> +static int check_address(unsigned long addr)
> +{
> + pgd_t *pgd = pgd_offset_k(addr);
> + pud_t *pud;
> + pmd_t *pmd;
> + pte_t *pte;
> + int ret = -EFAULT;
> +
> + if (pgd_none(*pgd))
> + goto out;
> +
> + pud = pud_offset(pgd, addr);
> + if (pud_none(*pud))
> + goto out;
> +
> + if (pud_sect(*pud)) {
> + pmd = pmd_alloc_one(&init_mm, addr);
> + if (!pmd) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + split_pud(pud, pmd);
> + pud_populate(&init_mm, pud, pmd);
> + }
> +
> + pmd = pmd_offset(pud, addr);
> + if (pmd_none(*pmd))
> + goto out;
> +
> + if (pmd_sect(*pmd)) {
> + pte = pte_alloc_one_kernel(&init_mm, addr);
> + if (!pte) {
> + ret = -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))
> + goto out;
> +
> + flush_tlb_all();
> + ret = 0;
> +
> +out:
> + return ret;
> +}
> +#else
> +static int check_address(unsigned long addr)
> +{
> + if (addr < MODULES_VADDR || addr >= MODULES_END)
> + return -EINVAL;
> +
> + return 0;
> +}
> +#endif
> +
> static int change_memory_common(unsigned long addr, int numpages,
> pgprot_t set_mask, pgprot_t clear_mask)
> {
> @@ -45,17 +108,18 @@ static int change_memory_common(unsigned long addr, int numpages,
> int ret;
> struct page_change_data data;
>
> + if (addr < PAGE_OFFSET && !is_vmalloc_addr((void *)addr))
> + return -EINVAL;
> +
> if (!IS_ALIGNED(addr, PAGE_SIZE)) {
> start &= PAGE_MASK;
> end = start + size;
> WARN_ON_ONCE(1);
> }
>
> - if (start < MODULES_VADDR || start >= MODULES_END)
> - return -EINVAL;
> -
> - if (end < MODULES_VADDR || end >= MODULES_END)
> - return -EINVAL;
> + ret = check_address(addr);
> + if (ret)
> + return ret;
>
> data.set_mask = set_mask;
> data.clear_mask = clear_mask;

Hi Laura

This patch seems vaild, but I didn't feel very reasonable.
Because of the large page to make TLB performance better, just
split it if it is necessary.therefore, I think the first thing
we try to keep it, if they fail ,and then to split.

thanks
zhongjiang