linux/arch/s390/kernel/kprobes_insn_page.S

/* 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
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> 2020-09-18 08:26:19 +00:00			`/* 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`