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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: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2020-09-18 10:26:19 +02:00 committed by Vasily Gorbik
parent eefc69a09c
commit b61e1f3281
4 changed files with 27 additions and 4 deletions
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1
arch/s390/kernel/Makefile
View File

@ -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

2
arch/s390/kernel/entry.h
View File

@ -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 */

6
arch/s390/kernel/kprobes.c
View File

@ -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);
}

22
arch/s390/kernel/kprobes_insn_page.S Normal file
View File

@ -0,0 +1,22 @@
/* 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