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arm64: proton-pack: Report Spectre-BHB vulnerabilities as part of Spectre-v2

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Speculation attacks against some high-performance processors can
make use of branch history to influence future speculation as part of
a spectre-v2 attack. This is not mitigated by CSV2, meaning CPUs that
previously reported 'Not affected' are now moderately mitigated by CSV2.

Update the value in /sys/devices/system/cpu/vulnerabilities/spectre_v2
to also show the state of the BHB mitigation.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
This commit is contained in:
James Morse 2022-02-08 16:08:13 +00:00
parent bd09128d16
commit dee435be76
2 changed files with 36 additions and 2 deletions
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2
arch/arm64/include/asm/spectre.h
View File

@ -93,5 +93,7 @@ void spectre_v4_enable_task_mitigation(struct task_struct *tsk);
enum mitigation_state arm64_get_meltdown_state(void);
enum mitigation_state arm64_get_spectre_bhb_state(void);
#endif /* __ASSEMBLY__ */
#endif /* __ASM_SPECTRE_H */

36
arch/arm64/kernel/proton-pack.c
View File

@ -96,14 +96,39 @@ static bool spectre_v2_mitigations_off(void)
return ret;
}
static const char *get_bhb_affected_string(enum mitigation_state bhb_state)
{
switch (bhb_state) {
case SPECTRE_UNAFFECTED:
return "";
default:
case SPECTRE_VULNERABLE:
return ", but not BHB";
case SPECTRE_MITIGATED:
return ", BHB";
}
}
ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
char *buf)
{
enum mitigation_state bhb_state = arm64_get_spectre_bhb_state();
const char *bhb_str = get_bhb_affected_string(bhb_state);
const char *v2_str = "Branch predictor hardening";
switch (spectre_v2_state) {
case SPECTRE_UNAFFECTED:
return sprintf(buf, "Not affected\n");
if (bhb_state == SPECTRE_UNAFFECTED)
return sprintf(buf, "Not affected\n");
/*
* Platforms affected by Spectre-BHB can't report
* "Not affected" for Spectre-v2.
*/
v2_str = "CSV2";
fallthrough;
case SPECTRE_MITIGATED:
return sprintf(buf, "Mitigation: Branch predictor hardening\n");
return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str);
case SPECTRE_VULNERABLE:
fallthrough;
default:
@ -771,6 +796,13 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
}
}
static enum mitigation_state spectre_bhb_state;
enum mitigation_state arm64_get_spectre_bhb_state(void)
{
return spectre_bhb_state;
}
/* Patched to NOP when enabled */
void noinstr spectre_bhb_patch_loop_mitigation_enable(struct alt_instr *alt,
__le32 *origptr,