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>

1 files changed, 26 insertions, 6 deletions

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index bc96c8a7fc79..b63baa749609 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -14,7 +14,9 @@
 
 #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"
 
@@ -22,8 +24,6 @@
 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);
+}