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Date: Wed, 4 Nov 2015 11:17:07 +0800 From: zhong jiang <zhongjiang@...wei.com> To: Laura Abbott <labbott@...oraproject.org> CC: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Xishi Qiu <qiuxishi@...wei.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, "Mark Rutland" <mark.rutland@....com> Subject: Re: [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@...oraproject.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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