Commit 2f0e8aae authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Vasily Gorbik
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s390/mm: rework memcpy_real() to avoid DAT-off mode 



Function memcpy_real() is an univeral data mover that does not
require DAT mode to be able reading from a physical address.
Its advantage is an ability to read from any address, even
those for which no kernel virtual mapping exists.

Although memcpy_real() is interrupt-safe, there are no handlers
that make use of this function. The compiler instrumentation
have to be disabled and separate no-DAT stack used to allow
execution of the function once DAT mode is disabled.

Rework memcpy_real() to overcome these shortcomings. As result,
data copying (which is primarily reading out a crashed system
memory by a user process) is executed on a regular stack with
enabled interrupts. Also, use of memcpy_real_buf swap buffer
becomes unnecessary and the swapping is eliminated.

The above is achieved by using a fixed virtual address range
that spans a single page and remaps that page repeatedly when
memcpy_real() is called for a particular physical address.

Reviewed-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent 14a3a262

arch/s390/boot/startup.c

+4 −1
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 


unsigned long __bootdata_preserved(__kaslr_offset);

unsigned long __bootdata_preserved(__abs_lowcore);

unsigned long __bootdata_preserved(__memcpy_real_area);

unsigned long __bootdata(__amode31_base);

unsigned long __bootdata_preserved(VMALLOC_START);

unsigned long __bootdata_preserved(VMALLOC_END);
@@ -182,7 +183,9 @@ static void setup_kernel_memory_layout(void) 
	/* force vmalloc and modules below kasan shadow */

	vmax = min(vmax, KASAN_SHADOW_START);

#endif

	__abs_lowcore = round_down(vmax - ABS_LOWCORE_MAP_SIZE, sizeof(struct lowcore));

	__memcpy_real_area = round_down(vmax - PAGE_SIZE, PAGE_SIZE);

	__abs_lowcore = round_down(__memcpy_real_area - ABS_LOWCORE_MAP_SIZE,

				   sizeof(struct lowcore));

	MODULES_END = round_down(__abs_lowcore, _SEGMENT_SIZE);

	MODULES_VADDR = MODULES_END - MODULES_LEN;

	VMALLOC_END = MODULES_VADDR;

arch/s390/include/asm/maccess.h

0 → 100644
+14 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef __ASM_S390_MACCESS_H

#define __ASM_S390_MACCESS_H



#include <linux/types.h>



struct iov_iter;



extern unsigned long __memcpy_real_area;

void memcpy_real_init(void);

size_t memcpy_real_iter(struct iov_iter *iter, unsigned long src, size_t count);

int memcpy_real(void *dest, unsigned long src, size_t count);



#endif /* __ASM_S390_MACCESS_H */

arch/s390/include/asm/pgtable.h

+1 −0
Original line number Diff line number Diff line
@@ -1780,6 +1780,7 @@ extern void vmem_remove_mapping(unsigned long start, unsigned long size); 
extern int __vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot, bool alloc);

extern int vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot);

extern void vmem_unmap_4k_page(unsigned long addr);

extern pte_t *vmem_get_alloc_pte(unsigned long addr, bool alloc);

extern int s390_enable_sie(void);

extern int s390_enable_skey(void);

extern void s390_reset_cmma(struct mm_struct *mm);

arch/s390/include/asm/processor.h

+0 −2
Original line number Diff line number Diff line
@@ -306,8 +306,6 @@ static __always_inline void __noreturn disabled_wait(void) 


#define ARCH_LOW_ADDRESS_LIMIT	0x7fffffffUL



extern int memcpy_real(void *, unsigned long, size_t);



extern int s390_isolate_bp(void);

extern int s390_isolate_bp_guest(void);

arch/s390/kernel/crash_dump.c

+2 −23
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
#include <asm/elf.h>

#include <asm/ipl.h>

#include <asm/sclp.h>

#include <asm/maccess.h>



#define PTR_ADD(x, y) (((char *) (x)) + ((unsigned long) (y)))

#define PTR_SUB(x, y) (((char *) (x)) - ((unsigned long) (y)))
@@ -53,8 +54,6 @@ struct save_area { 
};



static LIST_HEAD(dump_save_areas);

static DEFINE_MUTEX(memcpy_real_mutex);

static char memcpy_real_buf[PAGE_SIZE];



/*

 * Allocate a save area
@@ -116,26 +115,6 @@ void __init save_area_add_vxrs(struct save_area *sa, __vector128 *vxrs) 
	memcpy(sa->vxrs_high, vxrs + 16, 16 * sizeof(__vector128));

}



static size_t copy_to_iter_real(struct iov_iter *iter, unsigned long src, size_t count)

{

	size_t len, copied, res = 0;



	mutex_lock(&memcpy_real_mutex);

	while (count) {

		len = min(PAGE_SIZE, count);

		if (memcpy_real(memcpy_real_buf, src, len))

			break;

		copied = copy_to_iter(memcpy_real_buf, len, iter);

		count -= copied;

		src += copied;

		res += copied;

		if (copied < len)

			break;

	}

	mutex_unlock(&memcpy_real_mutex);

	return res;

}



size_t copy_oldmem_iter(struct iov_iter *iter, unsigned long src, size_t count)

{

	size_t len, copied, res = 0;
@@ -156,7 +135,7 @@ size_t copy_oldmem_iter(struct iov_iter *iter, unsigned long src, size_t count) 
			} else {

				len = count;

			}

			copied = copy_to_iter_real(iter, src, len);

			copied = memcpy_real_iter(iter, src, len);

		}

		count -= copied;

		src += copied;