Commit dee435be authored by James Morse's avatar James Morse
Browse files

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



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>
Signed-off-by: default avatarJames Morse <james.morse@arm.com>
parent bd09128d

arch/arm64/include/asm/spectre.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

arch/arm64/kernel/proton-pack.c

+34 −2
Original line number Diff line number Diff line
@@ -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:

		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,