Commit 98d2e153 authored by Takahiro Akashi's avatar Takahiro Akashi Committed by Catalin Marinas
Browse files

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: default avatarAKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 9b0aa14e

arch/arm64/kernel/machine_kexec.c

+26 −6
Original line number Diff line number Diff line
@@ -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);

}

arch/arm64/mm/mmu.c

+54 −49
Original line number Diff line number Diff line
@@ -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>
@@ -393,56 +395,11 @@ 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)

{

	phys_addr_t kernel_start = __pa_symbol(_text);

	phys_addr_t kernel_end = __pa_symbol(__init_begin);

	int flags = 0;



	if (debug_pagealloc_enabled())

		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;



	/*

	 * Take care not to create a writable alias for the

	 * read-only text and rodata sections of the kernel image.

	 */



	/* 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;

	}



	/*

	 * 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);



	/*

	 * Map the linear alias of the [_text, __init_begin) interval

	 * as non-executable now, and remove the write permission in

	 * mark_linear_text_alias_ro() below (which will be called after

	 * alternative patching has completed). This makes the contents

	 * of the region accessible to subsystems such as hibernate,

	 * but protects it from inadvertent modification or execution.

	 * 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);

	__create_pgd_mapping(pgd, start, __phys_to_virt(start), end - start,

			     prot, early_pgtable_alloc, flags);

}



void __init mark_linear_text_alias_ro(void)
@@ -457,7 +414,26 @@ void __init mark_linear_text_alias_ro(void) 


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())

		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;



	/*

	 * 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



	/* map all the memory banks */

	for_each_memblock(memory, reg) {
@@ -469,8 +445,37 @@ static void __init map_mem(pgd_t *pgd) 
		if (memblock_is_nomap(reg))

			continue;



		__map_memblock(pgd, start, end);

		__map_memblock(pgd, start, end, PAGE_KERNEL, flags);

	}



	/*

	 * Map the linear alias of the [_text, __init_begin) interval

	 * as non-executable now, and remove the write permission in

	 * mark_linear_text_alias_ro() below (which will be called after

	 * alternative patching has completed). This makes the contents

	 * of the region accessible to subsystems such as hibernate,

	 * but protects it from inadvertent modification or execution.

	 * Note that contiguous mappings cannot be remapped in this way,

	 * so we should avoid them here.

	 */

	__map_memblock(pgd, kernel_start, kernel_end,

		       PAGE_KERNEL, NO_CONT_MAPPINGS);

	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);



#ifdef CONFIG_KEXEC_CORE

	/*

	 * 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.

	 */

	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)

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