[linux-2.6-block.git] / arch / s390 / kernel / nospec-branch.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <linux/device.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 explicitely requested nobp=1, enable it and
		 * disable the expoline support.
		 */
		__set_facility(82, S390_lowcore.alt_stfle_fac_list);
		if (IS_ENABLED(CONFIG_EXPOLINE))
			nospec_disable = 1;
	} else {
		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
	}
	return 0;
}
early_param("nobp", nobp_setup_early);

static int __init nospec_setup_early(char *str)
{
	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
	return 0;
}
early_param("nospec", nospec_setup_early);

static int __init nospec_report(void)
{
	if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
		pr_info("Spectre V2 mitigation: execute trampolines\n");
	if (__test_facility(82, S390_lowcore.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 (IS_ENABLED(CC_USING_EXPOLINE)) {
		/*
		 * The kernel has been compiled with expolines.
		 * Keep expolines enabled and disable nobp.
		 */
		nospec_disable = 0;
		__clear_facility(82, S390_lowcore.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, S390_lowcore.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;
	u8 *instr, *thunk, *br;
	u8 insnbuf[6];
	s32 *epo;

	/* Second part of the instruction replace is always a nop */
	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 if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
			 thunk[6] == 0x44 && thunk[7] == 0x00 &&
			 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
			 (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
			/* larl %rx,<target br> + ex %r0,0(%rx) */
			br = thunk + (*(int *)(thunk + 2)) * 2;
		else
			continue;
		/* Check for unconditional branch 0x07f? or 0x47f???? */
		if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
			continue;

		memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
		switch (type) {
		case BRCL_EXPOLINE:
			insnbuf[0] = br[0];
			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
			if (br[0] == 0x47) {
				/* brcl to b, replace with bc + nopr */
				insnbuf[2] = br[2];
				insnbuf[3] = br[3];
			} else {
				/* brcl to br, replace with bcr + nop */
			}
			break;
		case BRASL_EXPOLINE:
			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
			if (br[0] == 0x47) {
				/* brasl to b, replace with bas + nopr */
				insnbuf[0] = 0x4d;
				insnbuf[2] = br[2];
				insnbuf[3] = br[3];
			} else {
				/* brasl to br, replace with basr + nop */
				insnbuf[0] = 0x0d;
			}
			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>
f19fbd5e MS	4	#include <asm/nospec-branch.h>
f19fbd5e MS	5
b2e2f43a MS	6	static int __init nobp_setup_early(char *str)
	7	{
	8	bool enabled;
	9	int rc;
	10
	11	rc = kstrtobool(str, &enabled);
	12	if (rc)
	13	return rc;
6e179d64 MS	14	if (enabled && test_facility(82)) {
	15	/*
	16	* The user explicitely requested nobp=1, enable it and
	17	* disable the expoline support.
	18	*/
b2e2f43a	19	__set_facility(82, S390_lowcore.alt_stfle_fac_list);
6e179d64 MS	20	if (IS_ENABLED(CONFIG_EXPOLINE))
	21	nospec_disable = 1;
	22	} else {
b2e2f43a	23	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
6e179d64	24	}
b2e2f43a MS	25	return 0;
	26	}
	27	early_param("nobp", nobp_setup_early);
	28
	29	static int __init nospec_setup_early(char *str)
	30	{
	31	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
	32	return 0;
	33	}
	34	early_param("nospec", nospec_setup_early);
	35
bc035599 MS	36	static int __init nospec_report(void)
	37	{
	38	if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
b7e7f505	39	pr_info("Spectre V2 mitigation: execute trampolines\n");
bc035599	40	if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
b7e7f505	41	pr_info("Spectre V2 mitigation: limited branch prediction\n");
bc035599 MS	42	return 0;
	43	}
	44	arch_initcall(nospec_report);
	45
b2e2f43a MS	46	#ifdef CONFIG_EXPOLINE
b2e2f43a MS	47
6e179d64	48	int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
f19fbd5e MS	49
	50	static int __init nospectre_v2_setup_early(char *str)
	51	{
6e179d64	52	nospec_disable = 1;
f19fbd5e MS	53	return 0;
	54	}
	55	early_param("nospectre_v2", nospectre_v2_setup_early);
	56
6a3d1e81	57	void __init nospec_auto_detect(void)
6e179d64 MS	58	{
	59	if (IS_ENABLED(CC_USING_EXPOLINE)) {
	60	/*
	61	* The kernel has been compiled with expolines.
	62	* Keep expolines enabled and disable nobp.
	63	*/
	64	nospec_disable = 0;
	65	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
	66	}
	67	/*
	68	* If the kernel has not been compiled with expolines the
	69	* nobp setting decides what is done, this depends on the
	70	* CONFIG_KERNEL_NP option and the nobp/nospec parameters.
	71	*/
6e179d64	72	}
6e179d64	73
f19fbd5e MS	74	static int __init spectre_v2_setup_early(char *str)
	75	{
	76	if (str && !strncmp(str, "on", 2)) {
6e179d64 MS	77	nospec_disable = 0;
6e179d64 MS	78	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
f19fbd5e	79	}
6e179d64 MS	80	if (str && !strncmp(str, "off", 3))
	81	nospec_disable = 1;
	82	if (str && !strncmp(str, "auto", 4))
6a3d1e81	83	nospec_auto_detect();
f19fbd5e MS	84	return 0;
	85	}
	86	early_param("spectre_v2", spectre_v2_setup_early);
	87
	88	static void __init_or_module __nospec_revert(s32 start, s32 end)
	89	{
	90	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
	91	u8 instr, thunk, *br;
	92	u8 insnbuf[6];
	93	s32 *epo;
	94
	95	/* Second part of the instruction replace is always a nop */
f19fbd5e MS	96	for (epo = start; epo < end; epo++) {
	97	instr = (u8 ) epo + epo;
	98	if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
	99	type = BRCL_EXPOLINE; /* brcl instruction */
	100	else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
	101	type = BRASL_EXPOLINE; /* brasl instruction */
	102	else
	103	continue;
	104	thunk = instr + ((int )(instr + 2)) * 2;
	105	if (thunk[0] == 0xc6 && thunk[1] == 0x00)
	106	/* exrl %r0,<target-br> */
	107	br = thunk + ((int )(thunk + 2)) * 2;
	108	else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
	109	thunk[6] == 0x44 && thunk[7] == 0x00 &&
	110	(thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
	111	(thunk[1] & 0xf0) == (thunk[8] & 0xf0))
	112	/* larl %rx,<target br> + ex %r0,0(%rx) */
	113	br = thunk + ((int )(thunk + 2)) * 2;
	114	else
	115	continue;
6deaa3bb MS	116	/* Check for unconditional branch 0x07f? or 0x47f???? */
6deaa3bb MS	117	if ((br[0] & 0xbf) != 0x07 \|\| (br[1] & 0xf0) != 0xf0)
f19fbd5e	118	continue;
6deaa3bb MS	119
6deaa3bb MS	120	memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
f19fbd5e MS	121	switch (type) {
f19fbd5e MS	122	case BRCL_EXPOLINE:
f19fbd5e MS	123	insnbuf[0] = br[0];
f19fbd5e MS	124	insnbuf[1] = (instr[1] & 0xf0) \| (br[1] & 0x0f);
6deaa3bb MS	125	if (br[0] == 0x47) {
	126	/* brcl to b, replace with bc + nopr */
	127	insnbuf[2] = br[2];
	128	insnbuf[3] = br[3];
	129	} else {
	130	/* brcl to br, replace with bcr + nop */
	131	}
f19fbd5e MS	132	break;
f19fbd5e MS	133	case BRASL_EXPOLINE:
f19fbd5e	134	insnbuf[1] = (instr[1] & 0xf0) \| (br[1] & 0x0f);
6deaa3bb MS	135	if (br[0] == 0x47) {
	136	/* brasl to b, replace with bas + nopr */
	137	insnbuf[0] = 0x4d;
	138	insnbuf[2] = br[2];
	139	insnbuf[3] = br[3];
	140	} else {
	141	/* brasl to br, replace with basr + nop */
	142	insnbuf[0] = 0x0d;
	143	}
f19fbd5e MS	144	break;
	145	}
	146
	147	s390_kernel_write(instr, insnbuf, 6);
	148	}
	149	}
	150
6e179d64	151	void __init_or_module nospec_revert(s32 start, s32 end)
f19fbd5e	152	{
6e179d64	153	if (nospec_disable)
f19fbd5e MS	154	__nospec_revert(start, end);
	155	}
	156
	157	extern s32 __nospec_call_start[], __nospec_call_end[];
	158	extern s32 __nospec_return_start[], __nospec_return_end[];
	159	void __init nospec_init_branches(void)
	160	{
6e179d64 MS	161	nospec_revert(__nospec_call_start, __nospec_call_end);
6e179d64 MS	162	nospec_revert(__nospec_return_start, __nospec_return_end);
f19fbd5e	163	}
b2e2f43a MS	164
b2e2f43a MS	165	#endif /* CONFIG_EXPOLINE */