linux-kernel - [PATCH v4 4/4] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Date:   Sun,  9 Jul 2017 20:37:42 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, keescook@...omium.org, matt@...eblueprint.co.uk,
        tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
        izumi.taku@...fujitsu.com, fanc.fnst@...fujitsu.com,
        thgarnie@...gle.com, Baoquan He <bhe@...hat.com>
Subject: [PATCH v4 4/4] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

Kernel text may be located in non-mirror regions (movable zone) when both
address range mirroring feature and KASLR are enabled.

The address range mirroring feature arranges such mirror region into
normal zone and other region into movable zone in order to locate
kernel code and data in mirror region. The physical memory region
whose descriptors in EFI memory map has EFI_MEMORY_MORE_RELIABLE
attribute (bit: 16) are mirrored.

If efi is detected, iterate efi memory map and pick the mirror region to
process for adding candidate of randomization slot. If efi is disabled
or no mirror region found, still process e820 memory map.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/boot/compressed/kaslr.c | 60 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 99c7194f7ea6..7376b3473758 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -37,7 +37,9 @@
 #include <linux/uts.h>
 #include <linux/utsname.h>
 #include <linux/ctype.h>
+#include <linux/efi.h>
 #include <generated/utsrelease.h>
+#include <asm/efi.h>
 
 /* Macros used by the included decompressor code below. */
 #define STATIC
@@ -558,6 +560,54 @@ static void process_mem_region(struct mem_vector *entry,
 	}
 }
 
+/* Marks if efi mirror regions have been found and handled. */
+static bool efi_mirror_found;
+
+static void process_efi_entries(unsigned long minimum,
+				unsigned long image_size)
+{
+	struct efi_info *e = &boot_params->efi_info;
+	struct mem_vector region;
+	efi_memory_desc_t *md;
+	unsigned long pmap;
+	char *signature;
+	u32 nr_desc;
+	int i;
+
+
+	signature = (char *)&boot_params->efi_info.efi_loader_signature;
+	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
+	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
+		return;
+
+#ifdef CONFIG_X86_32
+	/* Can't handle data above 4GB at this time */
+	if (e->efi_memmap_hi) {
+		warn("Memory map is above 4GB, EFI should be disabled.\n");
+		return;
+	}
+	pmap =  e->efi_memmap;
+#else
+	pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
+#endif
+
+	nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
+	for (i = 0; i < nr_desc; i++) {
+		md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
+		if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
+			region.start = md->phys_addr;
+			region.size = md->num_pages << EFI_PAGE_SHIFT;
+			process_mem_region(&region, minimum, image_size);
+			efi_mirror_found = true;
+
+			if (slot_area_index == MAX_SLOT_AREA) {
+				debug_putstr("Aborted efi scan (slot_areas full)!\n");
+				break;
+			}
+		}
+	}
+}
+
 static void process_e820_entries(unsigned long minimum,
 				 unsigned long image_size)
 {
@@ -586,13 +636,19 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
 {
 	/* Check if we had too many memmaps. */
 	if (memmap_too_large) {
-		debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
+		debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
 		return 0;
 	}
 
 	/* Make sure minimum is aligned. */
 	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
 
+#ifdef CONFIG_EFI
+	process_efi_entries(minimum, image_size);
+	if (efi_mirror_found)
+		return slots_fetch_random();
+#endif
+
 	process_e820_entries(minimum, image_size);
 	return slots_fetch_random();
 }
@@ -652,7 +708,7 @@ void choose_random_location(unsigned long input,
 	 */
 	min_addr = min(*output, 512UL << 20);
 
-	/* Walk e820 and find a random address. */
+	/* Walk available memory entries to find a random address. */
 	random_addr = find_random_phys_addr(min_addr, output_size);
 	if (!random_addr) {
 		warn("Physical KASLR disabled: no suitable memory region!");
-- 
2.5.5