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Commit 7b012f65 authored by James Morse's avatar James Morse Committed by Greg Kroah-Hartman
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arm64: proton-pack: Report Spectre-BHB vulnerabilities as part of Spectre-v2 



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: default avatarCatalin Marinas <catalin.marinas@arm.com>
[ code move to cpu_errata.c for backport ]
Signed-off-by: default avatarJames Morse <james.morse@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5b5ca260

arch/arm64/include/asm/cpufeature.h

+8 −0
Original line number Diff line number Diff line
@@ -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

arch/arm64/kernel/cpu_errata.c

+35 −3
Original line number Diff line number Diff line
@@ -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)

	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;

}