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    SubjectRe: [PATCH 2/2] arm64: Allow changing of attributes outside of modules
    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);

    Hi Laura,

    We only split the first page here, if the numpages is not 1, it's
    wrong, right?

    Thanks,
    Xishi Qiu

    > + if (ret)
    > + return ret;
    >
    > data.set_mask = set_mask;
    > data.clear_mask = clear_mask;





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