[linux-block.git] / arch / s390 / kernel / nospec-branch.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <asm/nospec-branch.h>

static int __init nobp_setup_early(char *str)
{
	bool enabled;
	int rc;

	rc = kstrtobool(str, &enabled);
	if (rc)
		return rc;
	if (enabled && test_facility(82)) {
		/*
		 * The user explicitly requested nobp=1, enable it and
		 * disable the expoline support.
		 */
		__set_facility(82, alt_stfle_fac_list);
		if (IS_ENABLED(CONFIG_EXPOLINE))
			nospec_disable = 1;
	} else {
		__clear_facility(82, alt_stfle_fac_list);
	}
	return 0;
}
early_param("nobp", nobp_setup_early);

static int __init nospec_setup_early(char *str)
{
	__clear_facility(82, alt_stfle_fac_list);
	return 0;
}
early_param("nospec", nospec_setup_early);

static int __init nospec_report(void)
{
	if (test_facility(156))
		pr_info("Spectre V2 mitigation: etokens\n");
	if (nospec_uses_trampoline())
		pr_info("Spectre V2 mitigation: execute trampolines\n");
	if (__test_facility(82, alt_stfle_fac_list))
		pr_info("Spectre V2 mitigation: limited branch prediction\n");
	return 0;
}
arch_initcall(nospec_report);

#ifdef CONFIG_EXPOLINE

int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);

static int __init nospectre_v2_setup_early(char *str)
{
	nospec_disable = 1;
	return 0;
}
early_param("nospectre_v2", nospectre_v2_setup_early);

void __init nospec_auto_detect(void)
{
	if (test_facility(156) || cpu_mitigations_off()) {
		/*
		 * The machine supports etokens.
		 * Disable expolines and disable nobp.
		 */
		if (__is_defined(CC_USING_EXPOLINE))
			nospec_disable = 1;
		__clear_facility(82, alt_stfle_fac_list);
	} else if (__is_defined(CC_USING_EXPOLINE)) {
		/*
		 * The kernel has been compiled with expolines.
		 * Keep expolines enabled and disable nobp.
		 */
		nospec_disable = 0;
		__clear_facility(82, alt_stfle_fac_list);
	}
	/*
	 * If the kernel has not been compiled with expolines the
	 * nobp setting decides what is done, this depends on the
	 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
	 */
}

static int __init spectre_v2_setup_early(char *str)
{
	if (str && !strncmp(str, "on", 2)) {
		nospec_disable = 0;
		__clear_facility(82, alt_stfle_fac_list);
	}
	if (str && !strncmp(str, "off", 3))
		nospec_disable = 1;
	if (str && !strncmp(str, "auto", 4))
		nospec_auto_detect();
	return 0;
}
early_param("spectre_v2", spectre_v2_setup_early);

static void __init_or_module __nospec_revert(s32 *start, s32 *end)
{
	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
	static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
	u8 *instr, *thunk, *br;
	u8 insnbuf[6];
	s32 *epo;

	/* Second part of the instruction replace is always a nop */
	memcpy(insnbuf + 2, branch, sizeof(branch));
	for (epo = start; epo < end; epo++) {
		instr = (u8 *) epo + *epo;
		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
			type = BRCL_EXPOLINE;	/* brcl instruction */
		else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
			type = BRASL_EXPOLINE;	/* brasl instruction */
		else
			continue;
		thunk = instr + (*(int *)(instr + 2)) * 2;
		if (thunk[0] == 0xc6 && thunk[1] == 0x00)
			/* exrl %r0,<target-br> */
			br = thunk + (*(int *)(thunk + 2)) * 2;
		else
			continue;
		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
			continue;
		switch (type) {
		case BRCL_EXPOLINE:
			/* brcl to thunk, replace with br + nop */
			insnbuf[0] = br[0];
			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
			break;
		case BRASL_EXPOLINE:
			/* brasl to thunk, replace with basr + nop */
			insnbuf[0] = 0x0d;
			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
			break;
		}

		s390_kernel_write(instr, insnbuf, 6);
	}
}

void __init_or_module nospec_revert(s32 *start, s32 *end)
{
	if (nospec_disable)
		__nospec_revert(start, end);
}

extern s32 __nospec_call_start[], __nospec_call_end[];
extern s32 __nospec_return_start[], __nospec_return_end[];
void __init nospec_init_branches(void)
{
	nospec_revert(__nospec_call_start, __nospec_call_end);
	nospec_revert(__nospec_return_start, __nospec_return_end);
}

#endif /* CONFIG_EXPOLINE */
Commit	Line	Data
f19fbd5e MS	1	// SPDX-License-Identifier: GPL-2.0
f19fbd5e MS	2	#include <linux/module.h>
d424986f	3	#include <linux/device.h>
0336e04a	4	#include <linux/cpu.h>
f19fbd5e MS	5	#include <asm/nospec-branch.h>
f19fbd5e MS	6
b2e2f43a MS	7	static int __init nobp_setup_early(char *str)
	8	{
	9	bool enabled;
	10	int rc;
	11
	12	rc = kstrtobool(str, &enabled);
	13	if (rc)
	14	return rc;
6e179d64 MS	15	if (enabled && test_facility(82)) {
6e179d64 MS	16	/*
cada938a	17	* The user explicitly requested nobp=1, enable it and
6e179d64 MS	18	* disable the expoline support.
6e179d64 MS	19	*/
17e89e13	20	__set_facility(82, alt_stfle_fac_list);
6e179d64 MS	21	if (IS_ENABLED(CONFIG_EXPOLINE))
	22	nospec_disable = 1;
	23	} else {
17e89e13	24	__clear_facility(82, alt_stfle_fac_list);
6e179d64	25	}
b2e2f43a MS	26	return 0;
	27	}
	28	early_param("nobp", nobp_setup_early);
	29
	30	static int __init nospec_setup_early(char *str)
	31	{
17e89e13	32	__clear_facility(82, alt_stfle_fac_list);
b2e2f43a MS	33	return 0;
	34	}
	35	early_param("nospec", nospec_setup_early);
	36
bc035599 MS	37	static int __init nospec_report(void)
bc035599 MS	38	{
aeaf7002 MS	39	if (test_facility(156))
aeaf7002 MS	40	pr_info("Spectre V2 mitigation: etokens\n");
5d17d4ed	41	if (nospec_uses_trampoline())
b7e7f505	42	pr_info("Spectre V2 mitigation: execute trampolines\n");
17e89e13	43	if (__test_facility(82, alt_stfle_fac_list))
b7e7f505	44	pr_info("Spectre V2 mitigation: limited branch prediction\n");
bc035599 MS	45	return 0;
	46	}
	47	arch_initcall(nospec_report);
	48
b2e2f43a MS	49	#ifdef CONFIG_EXPOLINE
b2e2f43a MS	50
6e179d64	51	int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
f19fbd5e MS	52
	53	static int __init nospectre_v2_setup_early(char *str)
	54	{
6e179d64	55	nospec_disable = 1;
f19fbd5e MS	56	return 0;
	57	}
	58	early_param("nospectre_v2", nospectre_v2_setup_early);
	59
6a3d1e81	60	void __init nospec_auto_detect(void)
6e179d64	61	{
0336e04a	62	if (test_facility(156) \|\| cpu_mitigations_off()) {
aeaf7002 MS	63	/*
	64	* The machine supports etokens.
	65	* Disable expolines and disable nobp.
	66	*/
475c8e9e	67	if (__is_defined(CC_USING_EXPOLINE))
aeaf7002	68	nospec_disable = 1;
17e89e13	69	__clear_facility(82, alt_stfle_fac_list);
475c8e9e	70	} else if (__is_defined(CC_USING_EXPOLINE)) {
6e179d64 MS	71	/*
	72	* The kernel has been compiled with expolines.
	73	* Keep expolines enabled and disable nobp.
	74	*/
	75	nospec_disable = 0;
17e89e13	76	__clear_facility(82, alt_stfle_fac_list);
6e179d64 MS	77	}
	78	/*
	79	* If the kernel has not been compiled with expolines the
	80	* nobp setting decides what is done, this depends on the
	81	* CONFIG_KERNEL_NP option and the nobp/nospec parameters.
	82	*/
6e179d64	83	}
6e179d64	84
f19fbd5e MS	85	static int __init spectre_v2_setup_early(char *str)
	86	{
	87	if (str && !strncmp(str, "on", 2)) {
6e179d64	88	nospec_disable = 0;
17e89e13	89	__clear_facility(82, alt_stfle_fac_list);
f19fbd5e	90	}
6e179d64 MS	91	if (str && !strncmp(str, "off", 3))
	92	nospec_disable = 1;
	93	if (str && !strncmp(str, "auto", 4))
6a3d1e81	94	nospec_auto_detect();
f19fbd5e MS	95	return 0;
	96	}
	97	early_param("spectre_v2", spectre_v2_setup_early);
	98
	99	static void __init_or_module __nospec_revert(s32 start, s32 end)
	100	{
	101	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
c74d3c18	102	static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
f19fbd5e MS	103	u8 instr, thunk, *br;
	104	u8 insnbuf[6];
	105	s32 *epo;
	106
	107	/* Second part of the instruction replace is always a nop */
2268169c	108	memcpy(insnbuf + 2, branch, sizeof(branch));
f19fbd5e MS	109	for (epo = start; epo < end; epo++) {
	110	instr = (u8 ) epo + epo;
	111	if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
	112	type = BRCL_EXPOLINE; /* brcl instruction */
	113	else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
	114	type = BRASL_EXPOLINE; /* brasl instruction */
	115	else
	116	continue;
	117	thunk = instr + ((int )(instr + 2)) * 2;
	118	if (thunk[0] == 0xc6 && thunk[1] == 0x00)
	119	/* exrl %r0,<target-br> */
	120	br = thunk + ((int )(thunk + 2)) * 2;
f19fbd5e MS	121	else
f19fbd5e MS	122	continue;
2268169c	123	if (br[0] != 0x07 \|\| (br[1] & 0xf0) != 0xf0)
f19fbd5e MS	124	continue;
	125	switch (type) {
	126	case BRCL_EXPOLINE:
2268169c	127	/* brcl to thunk, replace with br + nop */
f19fbd5e MS	128	insnbuf[0] = br[0];
	129	insnbuf[1] = (instr[1] & 0xf0) \| (br[1] & 0x0f);
	130	break;
	131	case BRASL_EXPOLINE:
2268169c VG	132	/* brasl to thunk, replace with basr + nop */
2268169c VG	133	insnbuf[0] = 0x0d;
f19fbd5e MS	134	insnbuf[1] = (instr[1] & 0xf0) \| (br[1] & 0x0f);
	135	break;
	136	}
	137
	138	s390_kernel_write(instr, insnbuf, 6);
	139	}
	140	}
	141
6e179d64	142	void __init_or_module nospec_revert(s32 start, s32 end)
f19fbd5e	143	{
6e179d64	144	if (nospec_disable)
f19fbd5e MS	145	__nospec_revert(start, end);
	146	}
	147
	148	extern s32 __nospec_call_start[], __nospec_call_end[];
	149	extern s32 __nospec_return_start[], __nospec_return_end[];
	150	void __init nospec_init_branches(void)
	151	{
6e179d64 MS	152	nospec_revert(__nospec_call_start, __nospec_call_end);
6e179d64 MS	153	nospec_revert(__nospec_return_start, __nospec_return_end);
f19fbd5e	154	}
b2e2f43a MS	155
b2e2f43a MS	156	#endif /* CONFIG_EXPOLINE */