[RFC PATCH v9 07/13] arm64/mm: Add support for XPFO

[Khalid Aziz <khalid.aziz@oracle.com>]

From: Juerg Haefliger <juerg.haefliger@canonical.com>

Enable support for eXclusive Page Frame Ownership (XPFO) for arm64 and
provide a hook for updating a single kernel page table entry (which is
required by the generic XPFO code).

XPFO doesn't support section/contiguous mappings yet, so let's disable
it if XPFO is turned on.

Thanks to Laura Abbot for the simplification from v5, and Mark Rutland
for pointing out we need NO_CONT_MAPPINGS too.

CC: linux-arm-kernel@lists.infradead.org
Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Khalid Aziz <khalid@gonehiking.org>
---
 .../admin-guide/kernel-parameters.txt         |  2 +-
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/mm/Makefile                        |  2 +
 arch/arm64/mm/mmu.c                           |  2 +-
 arch/arm64/mm/xpfo.c                          | 66 +++++++++++++++++++
 5 files changed, 71 insertions(+), 2 deletions(-)
 create mode 100644 arch/arm64/mm/xpfo.c

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e65e3bc1efe0..9fcf8c83031a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2997,7 +2997,7 @@
 
 	nox2apic	[X86-64,APIC] Do not enable x2APIC mode.
 
-	noxpfo		[XPFO,X86-64] Disable eXclusive Page Frame
+	noxpfo		[XPFO,X86-64,ARM64] Disable eXclusive Page Frame
 			Ownership (XPFO) when CONFIG_XPFO is on. Physical
 			pages mapped into user applications will also be
 			mapped in the kernel's address space as if
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a4168d366127..9a8d8e649cf8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -174,6 +174,7 @@ config ARM64
 	select SWIOTLB
 	select SYSCTL_EXCEPTION_TRACE
 	select THREAD_INFO_IN_TASK
+	select ARCH_SUPPORTS_XPFO
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
index 849c1df3d214..cca3808d9776 100644
--- a/arch/arm64/mm/Makefile
+++ b/arch/arm64/mm/Makefile
@@ -12,3 +12,5 @@ KASAN_SANITIZE_physaddr.o	+= n
 
 obj-$(CONFIG_KASAN)		+= kasan_init.o
 KASAN_SANITIZE_kasan_init.o	:= n
+
+obj-$(CONFIG_XPFO)		+= xpfo.o
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b6f5aa52ac67..1673f7443d62 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -453,7 +453,7 @@ static void __init map_mem(pgd_t *pgdp)
 	struct memblock_region *reg;
 	int flags = 0;
 
-	if (rodata_full || debug_pagealloc_enabled())
+	if (rodata_full || debug_pagealloc_enabled() || xpfo_enabled())
 		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	/*
diff --git a/arch/arm64/mm/xpfo.c b/arch/arm64/mm/xpfo.c
new file mode 100644
index 000000000000..7866c5acfffb
--- /dev/null
+++ b/arch/arm64/mm/xpfo.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 Hewlett Packard Enterprise Development, L.P.
+ * Copyright (C) 2016 Brown University. All rights reserved.
+ *
+ * Authors:
+ *   Juerg Haefliger <juerg.haefliger@hpe.com>
+ *   Vasileios P. Kemerlis <vpk@cs.brown.edu>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+
+#include <asm/tlbflush.h>
+
+/*
+ * Lookup the page table entry for a virtual address and return a pointer to
+ * the entry. Based on x86 tree.
+ */
+static pte_t *lookup_address(unsigned long addr)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pgd = pgd_offset_k(addr);
+	if (pgd_none(*pgd))
+		return NULL;
+
+	pud = pud_offset(pgd, addr);
+	if (pud_none(*pud))
+		return NULL;
+
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd))
+		return NULL;
+
+	return pte_offset_kernel(pmd, addr);
+}
+
+/* Update a single kernel page table entry */
+inline void set_kpte(void *kaddr, struct page *page, pgprot_t prot)
+{
+	pte_t *pte = lookup_address((unsigned long)kaddr);
+
+	if (unlikely(!pte)) {
+		WARN(1, "xpfo: invalid address %p\n", kaddr);
+		return;
+	}
+
+	set_pte(pte, pfn_pte(page_to_pfn(page), prot));
+}
+EXPORT_SYMBOL_GPL(set_kpte);
+
+inline void xpfo_flush_kernel_tlb(struct page *page, int order)
+{
+	unsigned long kaddr = (unsigned long)page_address(page);
+	unsigned long size = PAGE_SIZE;
+
+	flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
+}
+EXPORT_SYMBOL_GPL(xpfo_flush_kernel_tlb);
-- 
2.17.1