linux_kernel/arch/powerpc/kernel/security.c

// SPDX-License-Identifier: GPL-2.0+
//
// Security related flags and so on.
//
// Copyright 2018, Michael Ellerman, IBM Corporation.

#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/seq_buf.h>

#include <asm/debugfs.h>
#include <asm/security_features.h>
#include <asm/setup.h>


unsigned long powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;

bool barrier_nospec_enabled;

static void enable_barrier_nospec(bool enable)
{
	barrier_nospec_enabled = enable;
	do_barrier_nospec_fixups(enable);
}

void setup_barrier_nospec(void)
{
	bool enable;

	/*
	 * It would make sense to check SEC_FTR_SPEC_BAR_ORI31 below as well.
	 * But there's a good reason not to. The two flags we check below are
	 * both are enabled by default in the kernel, so if the hcall is not
	 * functional they will be enabled.
	 * On a system where the host firmware has been updated (so the ori
	 * functions as a barrier), but on which the hypervisor (KVM/Qemu) has
	 * not been updated, we would like to enable the barrier. Dropping the
	 * check for SEC_FTR_SPEC_BAR_ORI31 achieves that. The only downside is
	 * we potentially enable the barrier on systems where the host firmware
	 * is not updated, but that's harmless as it's a no-op.
	 */
	enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
		 security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);

	enable_barrier_nospec(enable);
}

#ifdef CONFIG_DEBUG_FS
static int barrier_nospec_set(void *data, u64 val)
{
	switch (val) {
	case 0:
	case 1:
		break;
	default:
		return -EINVAL;
	}

	if (!!val == !!barrier_nospec_enabled)
		return 0;

	enable_barrier_nospec(!!val);

	return 0;
}

static int barrier_nospec_get(void *data, u64 *val)
{
	*val = barrier_nospec_enabled ? 1 : 0;
	return 0;
}

DEFINE_SIMPLE_ATTRIBUTE(fops_barrier_nospec,
			barrier_nospec_get, barrier_nospec_set, "%llu\n");

static __init int barrier_nospec_debugfs_init(void)
{
	debugfs_create_file("barrier_nospec", 0600, powerpc_debugfs_root, NULL,
			    &fops_barrier_nospec);
	return 0;
}
device_initcall(barrier_nospec_debugfs_init);
#endif /* CONFIG_DEBUG_FS */

ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
{
	bool thread_priv;

	thread_priv = security_ftr_enabled(SEC_FTR_L1D_THREAD_PRIV);

	if (rfi_flush || thread_priv) {
		struct seq_buf s;
		seq_buf_init(&s, buf, PAGE_SIZE - 1);

		seq_buf_printf(&s, "Mitigation: ");

		if (rfi_flush)
			seq_buf_printf(&s, "RFI Flush");

		if (rfi_flush && thread_priv)
			seq_buf_printf(&s, ", ");

		if (thread_priv)
			seq_buf_printf(&s, "L1D private per thread");

		seq_buf_printf(&s, "\n");

		return s.len;
	}

	if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
	    !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
		return sprintf(buf, "Not affected\n");

	return sprintf(buf, "Vulnerable\n");
}

ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf)
{
	if (!security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR))
		return sprintf(buf, "Not affected\n");

	if (barrier_nospec_enabled)
		return sprintf(buf, "Mitigation: __user pointer sanitization\n");

	return sprintf(buf, "Vulnerable\n");
}

ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
{
	bool bcs, ccd, ori;
	struct seq_buf s;

	seq_buf_init(&s, buf, PAGE_SIZE - 1);

	bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
	ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
	ori = security_ftr_enabled(SEC_FTR_SPEC_BAR_ORI31);

	if (bcs || ccd) {
		seq_buf_printf(&s, "Mitigation: ");

		if (bcs)
			seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");

		if (bcs && ccd)
			seq_buf_printf(&s, ", ");

		if (ccd)
			seq_buf_printf(&s, "Indirect branch cache disabled");
	} else
		seq_buf_printf(&s, "Vulnerable");

	if (ori)
		seq_buf_printf(&s, ", ori31 speculation barrier enabled");

	seq_buf_printf(&s, "\n");

	return s.len;
}

/*
 * Store-forwarding barrier support.
 */

static enum stf_barrier_type stf_enabled_flush_types;
static bool no_stf_barrier;
bool stf_barrier;

static int __init handle_no_stf_barrier(char *p)
{
	pr_info("stf-barrier: disabled on command line.");
	no_stf_barrier = true;
	return 0;
}

early_param("no_stf_barrier", handle_no_stf_barrier);

/* This is the generic flag used by other architectures */
static int __init handle_ssbd(char *p)
{
	if (!p || strncmp(p, "auto", 5) == 0 || strncmp(p, "on", 2) == 0 ) {
		/* Until firmware tells us, we have the barrier with auto */
		return 0;
	} else if (strncmp(p, "off", 3) == 0) {
		handle_no_stf_barrier(NULL);
		return 0;
	} else
		return 1;

	return 0;
}
early_param("spec_store_bypass_disable", handle_ssbd);

/* This is the generic flag used by other architectures */
static int __init handle_no_ssbd(char *p)
{
	handle_no_stf_barrier(NULL);
	return 0;
}
early_param("nospec_store_bypass_disable", handle_no_ssbd);

static void stf_barrier_enable(bool enable)
{
	if (enable)
		do_stf_barrier_fixups(stf_enabled_flush_types);
	else
		do_stf_barrier_fixups(STF_BARRIER_NONE);

	stf_barrier = enable;
}

void setup_stf_barrier(void)
{
	enum stf_barrier_type type;
	bool enable, hv;

	hv = cpu_has_feature(CPU_FTR_HVMODE);

	/* Default to fallback in case fw-features are not available */
	if (cpu_has_feature(CPU_FTR_ARCH_300))
		type = STF_BARRIER_EIEIO;
	else if (cpu_has_feature(CPU_FTR_ARCH_207S))
		type = STF_BARRIER_SYNC_ORI;
	else if (cpu_has_feature(CPU_FTR_ARCH_206))
		type = STF_BARRIER_FALLBACK;
	else
		type = STF_BARRIER_NONE;

	enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
		(security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR) ||
		 (security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) && hv));

	if (type == STF_BARRIER_FALLBACK) {
		pr_info("stf-barrier: fallback barrier available\n");
	} else if (type == STF_BARRIER_SYNC_ORI) {
		pr_info("stf-barrier: hwsync barrier available\n");
	} else if (type == STF_BARRIER_EIEIO) {
		pr_info("stf-barrier: eieio barrier available\n");
	}

	stf_enabled_flush_types = type;

	if (!no_stf_barrier)
		stf_barrier_enable(enable);
}

ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
{
	if (stf_barrier && stf_enabled_flush_types != STF_BARRIER_NONE) {
		const char *type;
		switch (stf_enabled_flush_types) {
		case STF_BARRIER_EIEIO:
			type = "eieio";
			break;
		case STF_BARRIER_SYNC_ORI:
			type = "hwsync";
			break;
		case STF_BARRIER_FALLBACK:
			type = "fallback";
			break;
		default:
			type = "unknown";
		}
		return sprintf(buf, "Mitigation: Kernel entry/exit barrier (%s)\n", type);
	}

	if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
	    !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
		return sprintf(buf, "Not affected\n");

	return sprintf(buf, "Vulnerable\n");
}

#ifdef CONFIG_DEBUG_FS
static int stf_barrier_set(void *data, u64 val)
{
	bool enable;

	if (val == 1)
		enable = true;
	else if (val == 0)
		enable = false;
	else
		return -EINVAL;

	/* Only do anything if we're changing state */
	if (enable != stf_barrier)
		stf_barrier_enable(enable);

	return 0;
}

static int stf_barrier_get(void *data, u64 *val)
{
	*val = stf_barrier ? 1 : 0;
	return 0;
}

DEFINE_SIMPLE_ATTRIBUTE(fops_stf_barrier, stf_barrier_get, stf_barrier_set, "%llu\n");

static __init int stf_barrier_debugfs_init(void)
{
	debugfs_create_file("stf_barrier", 0600, powerpc_debugfs_root, NULL, &fops_stf_barrier);
	return 0;
}
device_initcall(stf_barrier_debugfs_init);
#endif /* CONFIG_DEBUG_FS */