Skip to contentSkip to conversation

x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

PATCH Superseded Baoquan He 2 participants 8 messages Jul 13, 2017 – Jul 18, 2017 x86

v5 of 10 Superseded Latest is v10 →

lore
Share & tools
lore

Baoquan He

author
#0 lore raw

v5 cover x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

Our customer reported that Kernel text may be located on non-mirror region (movable zone) when both address range mirroring feature and KASLR are enabled.

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

So we need restrict kernel to be located inside mirror regions if it is existed.

The method is very simple. If efi is enabled, just iterate all efi memory map and pick mirror region to process for adding candidate of slot. No matter how many mirror regions or what size of mirror region are found, as long as mirror region is found, we won't enter into e820 processing code though mirror region might not big enough to provide different position for kernel. If efi disabled or no mirror region existed, still process e820 memory map. This won't bring much efficiency loss, at worst we just go through all efi memory maps and found no mirror.

Changelog:
v4->v5:
Refactor process_efi_entries code according to Kees's suggestion.

v3->v4:
Rearrange the old patch 1/2 to make it be done in three steps for easier review addcording to Kees's suggestion.

v2->v3:
Put process_efi_entry invocation inside the #ifdef CONFIG_EFI according to tglx's suggestion. Since the efi related code is meaningful only if CONFIG_EFI=y.

v1->v2:
Removed debug code.

Taku suggested that we should put kernel to mirrored region always whether or not "kernelcore=mirror" is specified since kernel text is important and mirrored region is reliable.

Change code according to kbuild report and Chao Fan's comment.

Baoquan He (4):
x86/boot/KASLR: Wrap e820 entries walking code into new function

    process_e820_entries()
  x86/boot/KASLR: Switch to pass struct mem_vector to
    process_e820_entry()

x86/boot/KASLR: Rename process_e820_entry() into process_mem_region() x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

 arch/x86/boot/compressed/kaslr.c | 125 ++++++++++++++++++++++++++++++---------
 1 file changed, 98 insertions(+), 27 deletions(-)
Signature · 1 line
2.5.5
author
#1 lore raw

PATCH v5 1/4 x86/boot/KASLR: Wrap e820 entries walking code into new function process_e820_entries()

The original function process_e820_entry() only takes care of each e820 entry passed.

And move the E820_TYPE_RAM checking logic into process_e820_entries().

And remove the redundent local variable 'addr' definition in find_random_phys_addr().

Signed-off-by Baoquan He <[email protected]>
Acked-by Kees Cook <[email protected]>
---
 arch/x86/boot/compressed/kaslr.c | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)
arch/x86/boot/compressed/kaslr.c +21 -17
index 91f27ab970ef..1485f48aeda1 100644
@@ -488,10 +488,6 @@ static void process_e820_entry(struct boot_e820_entry *entry,
 	unsigned long start_orig, end;
 	struct boot_e820_entry cur_entry;
 
-	/* Skip non-RAM entries. */
-	if (entry->type != E820_TYPE_RAM)
-		return;
-
 	/* On 32-bit, ignore entries entirely above our maximum. */
 	if (IS_ENABLED(CONFIG_X86_32) && entry->addr >= KERNEL_IMAGE_SIZE)
 		return;

@@ -562,12 +558,29 @@ static void process_e820_entry(struct boot_e820_entry *entry,
 	}
 }
 
-static unsigned long find_random_phys_addr(unsigned long minimum,
-					   unsigned long image_size)
+static void process_e820_entries(unsigned long minimum,
+				 unsigned long image_size)
 {
 	int i;
-	unsigned long addr;
+	struct boot_e820_entry *entry;
+
+	/* Verify potential e820 positions, appending to slots list. */
+	for (i = 0; i < boot_params->e820_entries; i++) {
+		entry = &boot_params->e820_table[i];
+		/* Skip non-RAM entries. */
+		if (entry->type != E820_TYPE_RAM)
+			continue;
+		process_e820_entry(entry, minimum, image_size);
+		if (slot_area_index == MAX_SLOT_AREA) {
+			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
+			break;
+		}
+	}
+}
 
+static unsigned long find_random_phys_addr(unsigned long minimum,
+					   unsigned long image_size)
+{
 	/* Check if we had too many memmaps. */
 	if (memmap_too_large) {
 		debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");

@@ -577,16 +590,7 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
 	/* Make sure minimum is aligned. */
 	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
 
-	/* Verify potential e820 positions, appending to slots list. */
-	for (i = 0; i < boot_params->e820_entries; i++) {
-		process_e820_entry(&boot_params->e820_table[i], minimum,
-				   image_size);
-		if (slot_area_index == MAX_SLOT_AREA) {
-			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
-			break;
-		}
-	}
-
+	process_e820_entries(minimum, image_size);
 	return slots_fetch_random();
 }
Signature · 1 line
2.5.5
author
#2 lore raw

PATCH v5 2/4 x86/boot/KASLR: Switch to pass struct mem_vector to process_e820_entry()

In reply to Baoquan He

This makes process_e820_entry() be able to process any kind of memory region.

Signed-off-by Baoquan He <[email protected]>
Acked-by Kees Cook <[email protected]>
---
 arch/x86/boot/compressed/kaslr.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)
arch/x86/boot/compressed/kaslr.c +14 -11
index 1485f48aeda1..36ff9f729c43 100644
@@ -479,31 +479,31 @@ static unsigned long slots_fetch_random(void)
 	return 0;
 }
 
-static void process_e820_entry(struct boot_e820_entry *entry,
+static void process_e820_entry(struct mem_vector *entry,
 			       unsigned long minimum,
 			       unsigned long image_size)
 {
 	struct mem_vector region, overlap;
 	struct slot_area slot_area;
 	unsigned long start_orig, end;
-	struct boot_e820_entry cur_entry;
+	struct mem_vector cur_entry;
 
 	/* On 32-bit, ignore entries entirely above our maximum. */
-	if (IS_ENABLED(CONFIG_X86_32) && entry->addr >= KERNEL_IMAGE_SIZE)
+	if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
 		return;
 
 	/* Ignore entries entirely below our minimum. */
-	if (entry->addr + entry->size < minimum)
+	if (entry->start + entry->size < minimum)
 		return;
 
 	/* Ignore entries above memory limit */
-	end = min(entry->size + entry->addr, mem_limit);
-	if (entry->addr >= end)
+	end = min(entry->size + entry->start, mem_limit);
+	if (entry->start >= end)
 		return;
-	cur_entry.addr = entry->addr;
-	cur_entry.size = end - entry->addr;
+	cur_entry.start = entry->start;
+	cur_entry.size = end - entry->start;
 
-	region.start = cur_entry.addr;
+	region.start = cur_entry.start;
 	region.size = cur_entry.size;
 
 	/* Give up if slot area array is full. */

@@ -518,7 +518,7 @@ static void process_e820_entry(struct boot_e820_entry *entry,
 		region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
 
 		/* Did we raise the address above this e820 region? */
-		if (region.start > cur_entry.addr + cur_entry.size)
+		if (region.start > cur_entry.start + cur_entry.size)
 			return;
 
 		/* Reduce size by any delta from the original address. */

@@ -562,6 +562,7 @@ static void process_e820_entries(unsigned long minimum,
 				 unsigned long image_size)
 {
 	int i;
+	struct mem_vector region;
 	struct boot_e820_entry *entry;
 
 	/* Verify potential e820 positions, appending to slots list. */

@@ -570,7 +571,9 @@ static void process_e820_entries(unsigned long minimum,
 		/* Skip non-RAM entries. */
 		if (entry->type != E820_TYPE_RAM)
 			continue;
-		process_e820_entry(entry, minimum, image_size);
+		region.start = entry->addr;
+		region.size = entry->size;
+		process_e820_entry(&region, minimum, image_size);
 		if (slot_area_index == MAX_SLOT_AREA) {
 			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
 			break;
Signature · 1 line
2.5.5
author
#3 lore raw

PATCH v5 3/4 x86/boot/KASLR: Rename process_e820_entry() into process_mem_region()

In reply to Baoquan He

Now process_e820_entry() is not limited to e820 entry processing, rename it to process_mem_region(). And adjust the code comment accordingly.

Signed-off-by Baoquan He <[email protected]>
Acked-by Kees Cook <[email protected]>
---
 arch/x86/boot/compressed/kaslr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
arch/x86/boot/compressed/kaslr.c +3 -3
index 36ff9f729c43..99c7194f7ea6 100644
@@ -479,7 +479,7 @@ static unsigned long slots_fetch_random(void)
 	return 0;
 }
 
-static void process_e820_entry(struct mem_vector *entry,
+static void process_mem_region(struct mem_vector *entry,
 			       unsigned long minimum,
 			       unsigned long image_size)
 {

@@ -517,7 +517,7 @@ static void process_e820_entry(struct mem_vector *entry,
 		/* Potentially raise address to meet alignment needs. */
 		region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
 
-		/* Did we raise the address above this e820 region? */
+		/* Did we raise the address above the passed in memory entry? */
 		if (region.start > cur_entry.start + cur_entry.size)
 			return;
 

@@ -573,7 +573,7 @@ static void process_e820_entries(unsigned long minimum,
 			continue;
 		region.start = entry->addr;
 		region.size = entry->size;
-		process_e820_entry(&region, minimum, image_size);
+		process_mem_region(&region, minimum, image_size);
 		if (slot_area_index == MAX_SLOT_AREA) {
 			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
 			break;
Signature · 1 line
2.5.5
author
#4 lore raw

PATCH v5 4/4 x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

In reply to Baoquan He

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 <[email protected]>
---
 arch/x86/boot/compressed/kaslr.c | 68 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 66 insertions(+), 2 deletions(-)
arch/x86/boot/compressed/kaslr.c +66 -2
index 99c7194f7ea6..9059b571eca1 100644
@@ -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 +560,65 @@ static void process_mem_region(struct mem_vector *entry,
 	}
 }
 
+#ifdef CONFIG_EFI
+/*
+ * Returns true if mirror region found (and must have been processed
+ * for slots adding)
+ */
+static bool process_efi_entries(unsigned long minimum,
+				unsigned long image_size)
+{
+	struct efi_info *e = &boot_params->efi_info;
+	bool efi_mirror_found = false;
+	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 false;
+
+#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 false;
+	}
+	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;
+			}
+		}
+	}
+
+	return efi_mirror_found;
+}
+#else
+static inline bool process_efi_entries(unsigned long minimum,
+				       unsigned long image_size)
+{
+	return false;
+}
+#endif
+
 static void process_e820_entries(unsigned long minimum,
 				 unsigned long image_size)
 {

@@ -586,13 +647,16 @@ 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);
 
+	if(process_efi_entries(minimum, image_size))
+		return slots_fetch_random();
+
 	process_e820_entries(minimum, image_size);
 	return slots_fetch_random();
 }

@@ -652,7 +716,7 @@ 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!");
Signature · 1 line
2.5.5
Reviewed-by on v5 4/4
#5 lore raw
Quoted 70 lines · Baoquan He

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 <[email protected]>
---
 arch/x86/boot/compressed/kaslr.c | 68 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 66 insertions(+), 2 deletions(-)
arch/x86/boot/compressed/kaslr.c +36 -0
index 99c7194f7ea6..9059b571eca1 100644
@@ -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 +560,65 @@ static void process_mem_region(struct mem_vector *entry,
        }
 }
 
+#ifdef CONFIG_EFI
+/*
+ * Returns true if mirror region found (and must have been processed
+ * for slots adding)
+ */
+static bool process_efi_entries(unsigned long minimum,
+                               unsigned long image_size)
+{
+       struct efi_info *e = &boot_params->efi_info;
+       bool efi_mirror_found = false;
+       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 false;
+
+#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 false;
+       }
+       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;

arch/x86/boot/compressed/kaslr.c static void process_mem_region(struct mem_vector *entry, · line 606

Quoted 10 lines
arch/x86/boot/compressed/kaslr.c +10 -0
+       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");

Should this text be capitalized to "EFI" or expanded to "EFI mirror"?

Quoted 21 lines
arch/x86/boot/compressed/kaslr.c +15 -0
+                               break;
+                       }
+               }
+       }
+
+       return efi_mirror_found;
+}
+#else
+static inline bool process_efi_entries(unsigned long minimum,
+                                      unsigned long image_size)
+{
+       return false;
+}
+#endif
+
 static void process_e820_entries(unsigned long minimum,
                                 unsigned long image_size)
 {

@@ -586,13 +647,16 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
 {
        /* Check if we had too many memmaps. */

arch/x86/boot/compressed/kaslr.c static unsigned long find_random_phys_addr(unsigned long minimum, · line 657

Quoted 10 lines
arch/x86/boot/compressed/kaslr.c +2 -1
        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);
 
+       if(process_efi_entries(minimum, image_size))

Style nit: space between "if" and "(".

Quoted 15 lines
arch/x86/boot/compressed/kaslr.c +3 -2
+               return slots_fetch_random();
+
        process_e820_entries(minimum, image_size);
        return slots_fetch_random();
 }

@@ -652,7 +716,7 @@ 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!");
--
Quoted 2 lines

2.5.5

Otherwise, looks fine to me for the KASLR piece; I can't speak specifically to the EFI logic. :)

Reviewed-by Kees Cook <[email protected]>

-Kees

Signature · 2 lines
Kees Cook
Pixel Security
author
#6 lore raw
Quoted 38 lines · Kees Cook
Quoted 38 lines
arch/x86/boot/compressed/kaslr.c +38 -0
+#ifdef CONFIG_EFI
+/*
+ * Returns true if mirror region found (and must have been processed
+ * for slots adding)
+ */
+static bool process_efi_entries(unsigned long minimum,
+                               unsigned long image_size)
+{
+       struct efi_info *e = &boot_params->efi_info;
+       bool efi_mirror_found = false;
+       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 false;
+
+#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 false;
+       }
+       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;
Quoted 8 lines

arch/x86/boot/compressed/kaslr.c static void process_mem_region(struct mem_vector *entry, · line 606

Quoted 6 lines
arch/x86/boot/compressed/kaslr.c +6 -0
+                       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");

Should this text be capitalized to "EFI" or expanded to "EFI mirror"?

Yeah, this should be capitalized. And it should be EFI mirror here, just later Naoya will add other features about EFI, not only EFI mirror. Let me change it to EFI mirror, and Naoya can rebase on it.

Many thanks for your reviewing, Kees!

Quoted 28 lines
Quoted 28 lines
arch/x86/boot/compressed/kaslr.c +16 -1
+                               break;
+                       }
+               }
+       }
+
+       return efi_mirror_found;
+}
+#else
+static inline bool process_efi_entries(unsigned long minimum,
+                                      unsigned long image_size)
+{
+       return false;
+}
+#endif
+
 static void process_e820_entries(unsigned long minimum,
                                 unsigned long image_size)
 {

@@ -586,13 +647,16 @@ 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;
        }
Quoted 6 lines

arch/x86/boot/compressed/kaslr.c static unsigned long find_random_phys_addr(unsigned long minimum, · line 657

Quoted 4 lines
arch/x86/boot/compressed/kaslr.c +1 -0
        /* Make sure minimum is aligned. */
        minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
 
+       if(process_efi_entries(minimum, image_size))

Style nit: space between "if" and "(".

Will change, could I forget running checkpatch script.

Quoted 22 lines
Quoted 16 lines
arch/x86/boot/compressed/kaslr.c +3 -2
+               return slots_fetch_random();
+
        process_e820_entries(minimum, image_size);
        return slots_fetch_random();
 }

@@ -652,7 +716,7 @@ 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!");
--
Quoted 2 lines

2.5.5

Otherwise, looks fine to me for the KASLR piece; I can't speak specifically to the EFI logic. :)

Quoted 1 line
Reviewed-by Kees Cook <[email protected]>

I will repost with the clean up change and adding your Reviewed-by since no functionality change. Will see if there will be any EFI related comment.

Thanks again for reviewing and great suggestions!

Thanks
Baoquan

author
#7 lore raw

PATCH v6 4/4 x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

In reply to Baoquan He

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 <[email protected]>
Reviewed-by Kees Cook <[email protected]>

---
v5->v6:
Code style clean up according to Kees's comment.

 arch/x86/boot/compressed/kaslr.c | 68 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 66 insertions(+), 2 deletions(-)
arch/x86/boot/compressed/kaslr.c +66 -2
index 99c7194f7ea6..271b9632dd95 100644
@@ -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 +560,65 @@ static void process_mem_region(struct mem_vector *entry,
 	}
 }
 
+#ifdef CONFIG_EFI
+/*
+ * Returns true if mirror region found (and must have been processed
+ * for slots adding)
+ */
+static bool process_efi_entries(unsigned long minimum,
+				unsigned long image_size)
+{
+	struct efi_info *e = &boot_params->efi_info;
+	bool efi_mirror_found = false;
+	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 false;
+
+#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 false;
+	}
+	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;
+			}
+		}
+	}
+
+	return efi_mirror_found;
+}
+#else
+static inline bool process_efi_entries(unsigned long minimum,
+				       unsigned long image_size)
+{
+	return false;
+}
+#endif
+
 static void process_e820_entries(unsigned long minimum,
 				 unsigned long image_size)
 {

@@ -586,13 +647,16 @@ 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);
 
+	if (process_efi_entries(minimum, image_size))
+		return slots_fetch_random();
+
 	process_e820_entries(minimum, image_size);
 	return slots_fetch_random();
 }

@@ -652,7 +716,7 @@ 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!");
Signature · 1 line
2.5.5