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

[Laura Abbott]

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;
+	}
+
+	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;
-- 
2.5.0

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