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

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commit dee435be76f4117410bbd90573a881fd33488f37 upstream.

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>
[ code move to cpu_errata.c for backport ]
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
James Morse 2022-03-18 17:48:37 +00:00 committed by Greg Kroah-Hartman
parent 5b5ca2608f
commit 7b012f6597
2 changed files with 43 additions and 3 deletions
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8
arch/arm64/include/asm/cpufeature.h
View File

@ -527,6 +527,14 @@ static inline int arm64_get_ssbd_state(void)
void arm64_set_ssbd_mitigation(bool state);
/* Watch out, ordering is important here. */
enum mitigation_state {
SPECTRE_UNAFFECTED,
SPECTRE_MITIGATED,
SPECTRE_VULNERABLE,
};
enum mitigation_state arm64_get_spectre_bhb_state(void);
#endif /* __ASSEMBLY__ */
#endif

38
arch/arm64/kernel/cpu_errata.c
View File

@ -875,14 +875,39 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
}
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)
{
if (__spectrev2_safe)
return sprintf(buf, "Not affected\n");
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";
if (__spectrev2_safe) {
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";
}
if (__hardenbp_enab)
return sprintf(buf, "Mitigation: Branch predictor hardening\n");
return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str);
return sprintf(buf, "Vulnerable\n");
}
@ -903,3 +928,10 @@ ssize_t cpu_show_spec_store_bypass(struct device *dev,
return sprintf(buf, "Vulnerable\n");
}
static enum mitigation_state spectre_bhb_state;
enum mitigation_state arm64_get_spectre_bhb_state(void)
{
return spectre_bhb_state;
}