Commit b61e1f32 authored by Heiko Carstens's avatar Heiko Carstens Committed by Vasily Gorbik
Browse files

s390/kprobes: move insn_page to text segment 



Move the in-kernel kprobes insn page to text segment. Rationale:
having that page in rw data segment is suboptimal, since as soon as a
kprobe is set, this will split the 1:1 kernel mapping for a single
page which get new permissions.

Note: there is always at least one kprobe present for the kretprobe
trampoline; so the mapping will always be split into smaller 4k
mappings because of this.

Moving the kprobes insn page into text segment makes sure that the
page is mapped RO/X in any case, and avoids that the 1:1 mapping is
split.

The kprobe insn_page is defined as a dummy function which is filled
with "br %r14" instructions.

Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent eefc69a0

arch/s390/kernel/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ obj-$(CONFIG_COMPAT) += $(compat-obj-y) 
obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o

obj-$(CONFIG_STACKTRACE)	+= stacktrace.o

obj-$(CONFIG_KPROBES)		+= kprobes.o

obj-$(CONFIG_KPROBES)		+= kprobes_insn_page.o

obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o

obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o

obj-$(CONFIG_UPROBES)		+= uprobes.o

arch/s390/kernel/entry.h

+2 −0
Original line number Diff line number Diff line
@@ -87,4 +87,6 @@ void set_fs_fixup(void); 
unsigned long stack_alloc(void);

void stack_free(unsigned long stack);



extern char kprobes_insn_page[];



#endif /* _ENTRY_H */

arch/s390/kernel/kprobes.c

+2 −4
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <asm/set_memory.h>

#include <asm/sections.h>

#include <asm/dis.h>

#include "entry.h"



DEFINE_PER_CPU(struct kprobe *, current_kprobe);

DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
@@ -31,7 +32,6 @@ struct kretprobe_blackpoint kretprobe_blacklist[] = { }; 
DEFINE_INSN_CACHE_OPS(s390_insn);



static int insn_page_in_use;

static char insn_page[PAGE_SIZE] __aligned(PAGE_SIZE);



void *alloc_insn_page(void)

{
@@ -53,13 +53,11 @@ static void *alloc_s390_insn_page(void) 
{

	if (xchg(&insn_page_in_use, 1) == 1)

		return NULL;

	__set_memory((unsigned long) &insn_page, 1, SET_MEMORY_RO | SET_MEMORY_X);

	return &insn_page;

	return &kprobes_insn_page;

}



static void free_s390_insn_page(void *page)

{

	__set_memory((unsigned long) page, 1, SET_MEMORY_RW | SET_MEMORY_NX);

	xchg(&insn_page_in_use, 0);

}

arch/s390/kernel/kprobes_insn_page.S

0 → 100644
+22 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */



#include <linux/linkage.h>



/*

 * insn_page is a special 4k aligned dummy function for kprobes.

 * It will contain all kprobed instructions that are out-of-line executed.

 * The page must be within the kernel image to guarantee that the

 * out-of-line instructions are within 2GB distance of their original

 * location. Using a dummy function ensures that the insn_page is within

 * the text section of the kernel and mapped read-only/executable from

 * the beginning on, thus avoiding to split large mappings if the page

 * would be in the data section instead.

 */

	.section .kprobes.text, "ax"

	.align 4096

ENTRY(kprobes_insn_page)

	.rept 2048

	.word 0x07fe

	.endr

ENDPROC(kprobes_insn_page)

	.previous

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