[tip:efi/core] arm64/efi: Apply strict permissions to UEFI Runtime Services regions

[tip-bot for Ard Biesheuvel]

Commit-ID:  1fd55a9a09b0293af95ab4299b108f030fef4464
Gitweb:     http://git.kernel.org/tip/1fd55a9a09b0293af95ab4299b108f030fef4464
Author:     Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
AuthorDate: Mon, 25 Apr 2016 21:06:43 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 28 Apr 2016 11:33:53 +0200

arm64/efi: Apply strict permissions to UEFI Runtime Services regions

Recent UEFI versions expose permission attributes for runtime services
memory regions, either in the UEFI memory map or in the separate memory
attributes table. This allows the kernel to map these regions with
stricter permissions, rather than the RWX permissions that are used by
default. So wire this up in our mapping routine.

Note that in the absence of permission attributes, we still only map
regions of type EFI_RUNTIME_SERVICE_CODE with the executable bit set.
Also, we base the mapping attributes of EFI_MEMORY_MAPPED_IO on the
type directly rather than on the absence of the EFI_MEMORY_WB attribute.
This is more correct, but is also required for compatibility with the
upcoming support for the Memory Attributes Table, which only carries
permission attributes, not memory type attributes.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Peter Jones <pjones@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1461614832-17633-12-git-send-email-matt@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/arm64/kernel/efi.c | 54 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index b6abc85..33a6da1 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -17,22 +17,48 @@
 
 #include <asm/efi.h>
 
-int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
+/*
+ * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
+ * executable, everything else can be mapped with the XN bits
+ * set. Also take the new (optional) RO/XP bits into account.
+ */
+static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
 {
-	pteval_t prot_val;
+	u64 attr = md->attribute;
+	u32 type = md->type;
 
-	/*
-	 * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
-	 * executable, everything else can be mapped with the XN bits
-	 * set.
-	 */
-	if ((md->attribute & EFI_MEMORY_WB) == 0)
-		prot_val = PROT_DEVICE_nGnRE;
-	else if (md->type == EFI_RUNTIME_SERVICES_CODE ||
-		 !PAGE_ALIGNED(md->phys_addr))
-		prot_val = pgprot_val(PAGE_KERNEL_EXEC);
-	else
-		prot_val = pgprot_val(PAGE_KERNEL);
+	if (type == EFI_MEMORY_MAPPED_IO)
+		return PROT_DEVICE_nGnRE;
+
+	if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
+		      "UEFI Runtime regions are not aligned to 64 KB -- buggy firmware?"))
+		/*
+		 * If the region is not aligned to the page size of the OS, we
+		 * can not use strict permissions, since that would also affect
+		 * the mapping attributes of the adjacent regions.
+		 */
+		return pgprot_val(PAGE_KERNEL_EXEC);
+
+	/* R-- */
+	if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
+	    (EFI_MEMORY_XP | EFI_MEMORY_RO))
+		return pgprot_val(PAGE_KERNEL_RO);
+
+	/* R-X */
+	if (attr & EFI_MEMORY_RO)
+		return pgprot_val(PAGE_KERNEL_ROX);
+
+	/* RW- */
+	if (attr & EFI_MEMORY_XP || type != EFI_RUNTIME_SERVICES_CODE)
+		return pgprot_val(PAGE_KERNEL);
+
+	/* RWX */
+	return pgprot_val(PAGE_KERNEL_EXEC);
+}
+
+int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
+{
+	pteval_t prot_val = create_mapping_protection(md);
 
 	create_pgd_mapping(mm, md->phys_addr, md->virt_addr,
 			   md->num_pages << EFI_PAGE_SHIFT,