arm64: kdump: protect crash dump kernel memory

arch_kexec_protect_crashkres() and arch_kexec_unprotect_crashkres()
are meant to be called by kexec_load() in order to protect the memory
allocated for crash dump kernel once the image is loaded.

The protection is implemented by unmapping the relevant segments in crash
dump kernel memory, rather than making it read-only as other archs do,
to prevent coherency issues due to potential cache aliasing (with
mismatched attributes).

Page-level mappings are consistently used here so that we can change
the attributes of segments in page granularity as well as shrink the region
also in page granularity through /sys/kernel/kexec_crash_size, putting
the freed memory back to buddy system.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/machine_kexec.c

@@ -14,16 +14,16 @@
 
 #include <asm/cacheflush.h>
 #include <asm/cpu_ops.h>
+#include <asm/mmu.h>
 #include <asm/mmu_context.h>
+#include <asm/page.h>
 
 #include "cpu-reset.h"
 
 /* Global variables for the arm64_relocate_new_kernel routine. */
 extern const unsigned char arm64_relocate_new_kernel[];
 extern const unsigned long arm64_relocate_new_kernel_size;
 
-static unsigned long kimage_start;
-
 /**
  * kexec_image_info - For debugging output.
  */
@@ -64,8 +64,6 @@ void machine_kexec_cleanup(struct kimage *kimage)
  */
 int machine_kexec_prepare(struct kimage *kimage)
 {
-	kimage_start = kimage->start;
-
 	kexec_image_info(kimage);
 
 	if (kimage->type != KEXEC_TYPE_CRASH && cpus_are_stuck_in_kernel()) {
@@ -183,7 +181,7 @@ void machine_kexec(struct kimage *kimage)
 	kexec_list_flush(kimage);
 
 	/* Flush the new image if already in place. */
-	if (kimage->head & IND_DONE)
+	if ((kimage != kexec_crash_image) && (kimage->head & IND_DONE))
 		kexec_segment_flush(kimage);
 
 	pr_info("Bye!\n");
@@ -201,7 +199,7 @@ void machine_kexec(struct kimage *kimage)
 	 */
 
 	cpu_soft_restart(1, reboot_code_buffer_phys, kimage->head,
-		kimage_start, 0);
+		kimage->start, 0);
 
 	BUG(); /* Should never get here. */
 }
@@ -210,3 +208,25 @@ void machine_crash_shutdown(struct pt_regs *regs)
 {
 	/* Empty routine needed to avoid build errors. */
 }
+
+void arch_kexec_protect_crashkres(void)
+{
+	int i;
+
+	kexec_segment_flush(kexec_crash_image);
+
+	for (i = 0; i < kexec_crash_image->nr_segments; i++)
+		set_memory_valid(
+			__phys_to_virt(kexec_crash_image->segment[i].mem),
+			kexec_crash_image->segment[i].memsz >> PAGE_SHIFT, 0);
+}
+
+void arch_kexec_unprotect_crashkres(void)
+{
+	int i;
+
+	for (i = 0; i < kexec_crash_image->nr_segments; i++)
+		set_memory_valid(
+			__phys_to_virt(kexec_crash_image->segment[i].mem),
+			kexec_crash_image->segment[i].memsz >> PAGE_SHIFT, 1);
+}

arch/arm64/mm/mmu.c

@@ -22,6 +22,8 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/init.h>
+#include <linux/ioport.h>
+#include <linux/kexec.h>
 #include <linux/libfdt.h>
 #include <linux/mman.h>
 #include <linux/nodemask.h>
@@ -393,10 +395,28 @@ static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
 	flush_tlb_kernel_range(virt, virt + size);
 }
 
-static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end)
+static void __init __map_memblock(pgd_t *pgd, phys_addr_t start,
+				  phys_addr_t end, pgprot_t prot, int flags)
+{
+	__create_pgd_mapping(pgd, start, __phys_to_virt(start), end - start,
+			     prot, early_pgtable_alloc, flags);
+}
+
+void __init mark_linear_text_alias_ro(void)
+{
+	/*
+	 * Remove the write permissions from the linear alias of .text/.rodata
+	 */
+	update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text),
+			    (unsigned long)__init_begin - (unsigned long)_text,
+			    PAGE_KERNEL_RO);
+}
+
+static void __init map_mem(pgd_t *pgd)
 {
 	phys_addr_t kernel_start = __pa_symbol(_text);
 	phys_addr_t kernel_end = __pa_symbol(__init_begin);
+	struct memblock_region *reg;
 	int flags = 0;
 
 	if (debug_pagealloc_enabled())
@@ -405,30 +425,28 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
 	/*
 	 * Take care not to create a writable alias for the
 	 * read-only text and rodata sections of the kernel image.
+	 * So temporarily mark them as NOMAP to skip mappings in
+	 * the following for-loop
 	 */
+	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
+#ifdef CONFIG_KEXEC_CORE
+	if (crashk_res.end)
+		memblock_mark_nomap(crashk_res.start,
+				    resource_size(&crashk_res));
+#endif
 
-	/* No overlap with the kernel text/rodata */
-	if (end < kernel_start || start >= kernel_end) {
-		__create_pgd_mapping(pgd, start, __phys_to_virt(start),
-				     end - start, PAGE_KERNEL,
-				     early_pgtable_alloc, flags);
-		return;
-	}
+	/* map all the memory banks */
+	for_each_memblock(memory, reg) {
+		phys_addr_t start = reg->base;
+		phys_addr_t end = start + reg->size;
 
-	/*
-	 * This block overlaps the kernel text/rodata mappings.
-	 * Map the portion(s) which don't overlap.
-	 */
-	if (start < kernel_start)
-		__create_pgd_mapping(pgd, start,
-				     __phys_to_virt(start),
-				     kernel_start - start, PAGE_KERNEL,
-				     early_pgtable_alloc, flags);
-	if (kernel_end < end)
-		__create_pgd_mapping(pgd, kernel_end,
-				     __phys_to_virt(kernel_end),
-				     end - kernel_end, PAGE_KERNEL,
-				     early_pgtable_alloc, flags);
+		if (start >= end)
+			break;
+		if (memblock_is_nomap(reg))
+			continue;
+
+		__map_memblock(pgd, start, end, PAGE_KERNEL, flags);
+	}
 
 	/*
 	 * Map the linear alias of the [_text, __init_begin) interval
@@ -440,37 +458,24 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
 	 * Note that contiguous mappings cannot be remapped in this way,
 	 * so we should avoid them here.
 	 */
-	__create_pgd_mapping(pgd, kernel_start, __phys_to_virt(kernel_start),
-			     kernel_end - kernel_start, PAGE_KERNEL,
-			     early_pgtable_alloc, NO_CONT_MAPPINGS);
-}
+	__map_memblock(pgd, kernel_start, kernel_end,
+		       PAGE_KERNEL, NO_CONT_MAPPINGS);
+	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
 
-void __init mark_linear_text_alias_ro(void)
-{
+#ifdef CONFIG_KEXEC_CORE
 	/*
-	 * Remove the write permissions from the linear alias of .text/.rodata
+	 * Use page-level mappings here so that we can shrink the region
+	 * in page granularity and put back unused memory to buddy system
+	 * through /sys/kernel/kexec_crash_size interface.
 	 */
-	update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text),
-			    (unsigned long)__init_begin - (unsigned long)_text,
-			    PAGE_KERNEL_RO);
-}
-
-static void __init map_mem(pgd_t *pgd)
-{
-	struct memblock_region *reg;
-
-	/* map all the memory banks */
-	for_each_memblock(memory, reg) {
-		phys_addr_t start = reg->base;
-		phys_addr_t end = start + reg->size;
-
-		if (start >= end)
-			break;
-		if (memblock_is_nomap(reg))
-			continue;
-
-		__map_memblock(pgd, start, end);
+	if (crashk_res.end) {
+		__map_memblock(pgd, crashk_res.start, crashk_res.end + 1,
+			       PAGE_KERNEL,
+			       NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
+		memblock_clear_nomap(crashk_res.start,
+				     resource_size(&crashk_res));
 	}
+#endif
 }
 
 void mark_rodata_ro(void)