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Commit 3a64e6a9 authored by Marc Zyngier's avatar Marc Zyngier Committed by Greg Kroah-Hartman
Browse files

arm64: Add 'ssbd' command-line option 



commit a43ae4dfe56a01f5b98ba0cb2f784b6a43bafcc6 upstream.

On a system where the firmware implements ARCH_WORKAROUND_2,
it may be useful to either permanently enable or disable the
workaround for cases where the user decides that they'd rather
not get a trap overhead, and keep the mitigation permanently
on or off instead of switching it on exception entry/exit.

In any case, default to the mitigation being enabled.

Reviewed-by: default avatarJulien Grall <julien.grall@arm.com>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e7037bd9

Documentation/kernel-parameters.txt

+17 −0
Original line number Diff line number Diff line
@@ -4023,6 +4023,23 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
	spia_pedr=

	spia_peddr=



	ssbd=		[ARM64,HW]

			Speculative Store Bypass Disable control



			On CPUs that are vulnerable to the Speculative

			Store Bypass vulnerability and offer a

			firmware based mitigation, this parameter

			indicates how the mitigation should be used:



			force-on:  Unconditionally enable mitigation for

				   for both kernel and userspace

			force-off: Unconditionally disable mitigation for

				   for both kernel and userspace

			kernel:    Always enable mitigation in the

				   kernel, and offer a prctl interface

				   to allow userspace to register its

				   interest in being mitigated too.



	stack_guard_gap=	[MM]

			override the default stack gap protection. The value

			is in page units and it defines how many pages prior

arch/arm64/include/asm/cpufeature.h

+6 −0
Original line number Diff line number Diff line
@@ -221,6 +221,12 @@ static inline bool system_supports_mixed_endian_el0(void) 
	return id_aa64mmfr0_mixed_endian_el0(read_system_reg(SYS_ID_AA64MMFR0_EL1));

}



#define ARM64_SSBD_UNKNOWN		-1

#define ARM64_SSBD_FORCE_DISABLE	0

#define ARM64_SSBD_KERNEL		1

#define ARM64_SSBD_FORCE_ENABLE		2

#define ARM64_SSBD_MITIGATED		3



#endif /* __ASSEMBLY__ */



#endif

arch/arm64/kernel/cpu_errata.c

+87 −16
Original line number Diff line number Diff line
@@ -190,6 +190,38 @@ static int enable_smccc_arch_workaround_1(void *data) 
#ifdef CONFIG_ARM64_SSBD

DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);



int ssbd_state __read_mostly = ARM64_SSBD_KERNEL;



static const struct ssbd_options {

	const char	*str;

	int		state;

} ssbd_options[] = {

	{ "force-on",	ARM64_SSBD_FORCE_ENABLE, },

	{ "force-off",	ARM64_SSBD_FORCE_DISABLE, },

	{ "kernel",	ARM64_SSBD_KERNEL, },

};



static int __init ssbd_cfg(char *buf)

{

	int i;



	if (!buf || !buf[0])

		return -EINVAL;



	for (i = 0; i < ARRAY_SIZE(ssbd_options); i++) {

		int len = strlen(ssbd_options[i].str);



		if (strncmp(buf, ssbd_options[i].str, len))

			continue;



		ssbd_state = ssbd_options[i].state;

		return 0;

	}



	return -EINVAL;

}

early_param("ssbd", ssbd_cfg);



void __init arm64_update_smccc_conduit(struct alt_instr *alt,

				       __le32 *origptr, __le32 *updptr,

				       int nr_inst)
@@ -233,44 +265,83 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, 
				    int scope)

{

	struct arm_smccc_res res;

	bool supported = true;

	bool required = true;

	s32 val;



	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());



	if (psci_ops.smccc_version == SMCCC_VERSION_1_0)

	if (psci_ops.smccc_version == SMCCC_VERSION_1_0) {

		ssbd_state = ARM64_SSBD_UNKNOWN;

		return false;

	}



	/*

	 * The probe function return value is either negative

	 * (unsupported or mitigated), positive (unaffected), or zero

	 * (requires mitigation). We only need to do anything in the

	 * last case.

	 */

	switch (psci_ops.conduit) {

	case PSCI_CONDUIT_HVC:

		arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,

				  ARM_SMCCC_ARCH_WORKAROUND_2, &res);

		if ((int)res.a0 != 0)

			supported = false;

		break;



	case PSCI_CONDUIT_SMC:

		arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,

				  ARM_SMCCC_ARCH_WORKAROUND_2, &res);

		if ((int)res.a0 != 0)

			supported = false;

		break;



	default:

		supported = false;

		ssbd_state = ARM64_SSBD_UNKNOWN;

		return false;

	}



	if (supported) {

	val = (s32)res.a0;



	switch (val) {

	case SMCCC_RET_NOT_SUPPORTED:

		ssbd_state = ARM64_SSBD_UNKNOWN;

		return false;



	case SMCCC_RET_NOT_REQUIRED:

		pr_info_once("%s mitigation not required\n", entry->desc);

		ssbd_state = ARM64_SSBD_MITIGATED;

		return false;



	case SMCCC_RET_SUCCESS:

		required = true;

		break;



	case 1:	/* Mitigation not required on this CPU */

		required = false;

		break;



	default:

		WARN_ON(1);

		return false;

	}



	switch (ssbd_state) {

	case ARM64_SSBD_FORCE_DISABLE:

		pr_info_once("%s disabled from command-line\n", entry->desc);

		arm64_set_ssbd_mitigation(false);

		required = false;

		break;



	case ARM64_SSBD_KERNEL:

		if (required) {

			__this_cpu_write(arm64_ssbd_callback_required, 1);

			arm64_set_ssbd_mitigation(true);

		}

		break;



	case ARM64_SSBD_FORCE_ENABLE:

		pr_info_once("%s forced from command-line\n", entry->desc);

		arm64_set_ssbd_mitigation(true);

		required = true;

		break;



	default:

		WARN_ON(1);

		break;

	}



	return supported;

	return required;

}

#endif	/* CONFIG_ARM64_SSBD */