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// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <linux/device.h>
#include <asm/facility.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_SYSFS
ssize_t cpu_show_spectre_v1(struct device *dev,
struct device_attribute *attr, char *buf)
{
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
}
ssize_t cpu_show_spectre_v2(struct device *dev,
struct device_attribute *attr, char *buf)
{
if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
return sprintf(buf, "Mitigation: execute trampolines\n");
if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
return sprintf(buf, "Mitigation: limited branch prediction.\n");
return sprintf(buf, "Vulnerable\n");
}
#endif
#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);
static int __init spectre_v2_auto_early(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.
*/
return 0;
}
#ifdef CONFIG_EXPOLINE_AUTO
early_initcall(spectre_v2_auto_early);
#endif
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))
spectre_v2_auto_early();
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 */
memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4);
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;
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 */
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