[PATCHv2 2/2] arm64: Allow changing of attributes outside of modules
Xishi Qiu
qiuxishi at huawei.com
Fri Nov 13 00:27:25 PST 2015
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 at fedoraproject.org>
> ---
> 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;
> + }
> +
> + do {
> + next = pmd_addr_end(addr, end);
> + if (((addr | end) & ~SECTION_MASK) == 0) {
Hi Laura,
Why not like this?
if (pmd_sect(*pmd) && ((addr | nest) & ~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))
How about abstracting "start < MODULES_VADDR || start >= MODULES_END" to a new function?
e.g. is_module_addr(), however it is a little confusion with is_module_address().
> 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;
>
It will not filter this case, start in module range and end in vmalloc range, right?
start and end should be both in one range.
Thanks,
Xishi Qiu
> - 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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