af2e8c68b9
On some systems that are vulnerable to Spectre v2, it is up to software to flush the link stack (return address stack), in order to protect against Spectre-RSB. When exiting from a guest we do some house keeping and then potentially exit to C code which is several stack frames deep in the host kernel. We will then execute a series of returns without preceeding calls, opening up the possiblity that the guest could have poisoned the link stack, and direct speculative execution of the host to a gadget of some sort. To prevent this we add a flush of the link stack on exit from a guest. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
506 lines
13 KiB
C
506 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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//
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// Security related flags and so on.
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//
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// Copyright 2018, Michael Ellerman, IBM Corporation.
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#include <linux/cpu.h>
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#include <linux/kernel.h>
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#include <linux/device.h>
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#include <linux/seq_buf.h>
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#include <asm/asm-prototypes.h>
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#include <asm/code-patching.h>
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#include <asm/debugfs.h>
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#include <asm/security_features.h>
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#include <asm/setup.h>
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unsigned long powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;
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enum count_cache_flush_type {
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COUNT_CACHE_FLUSH_NONE = 0x1,
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COUNT_CACHE_FLUSH_SW = 0x2,
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COUNT_CACHE_FLUSH_HW = 0x4,
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};
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static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NONE;
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static bool link_stack_flush_enabled;
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bool barrier_nospec_enabled;
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static bool no_nospec;
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static bool btb_flush_enabled;
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#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
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static bool no_spectrev2;
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#endif
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static void enable_barrier_nospec(bool enable)
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{
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barrier_nospec_enabled = enable;
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do_barrier_nospec_fixups(enable);
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}
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void setup_barrier_nospec(void)
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{
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bool enable;
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/*
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* It would make sense to check SEC_FTR_SPEC_BAR_ORI31 below as well.
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* But there's a good reason not to. The two flags we check below are
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* both are enabled by default in the kernel, so if the hcall is not
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* functional they will be enabled.
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* On a system where the host firmware has been updated (so the ori
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* functions as a barrier), but on which the hypervisor (KVM/Qemu) has
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* not been updated, we would like to enable the barrier. Dropping the
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* check for SEC_FTR_SPEC_BAR_ORI31 achieves that. The only downside is
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* we potentially enable the barrier on systems where the host firmware
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* is not updated, but that's harmless as it's a no-op.
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*/
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enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
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security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);
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if (!no_nospec && !cpu_mitigations_off())
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enable_barrier_nospec(enable);
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}
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static int __init handle_nospectre_v1(char *p)
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{
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no_nospec = true;
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return 0;
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}
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early_param("nospectre_v1", handle_nospectre_v1);
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#ifdef CONFIG_DEBUG_FS
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static int barrier_nospec_set(void *data, u64 val)
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{
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switch (val) {
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case 0:
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case 1:
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break;
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default:
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return -EINVAL;
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}
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if (!!val == !!barrier_nospec_enabled)
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return 0;
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enable_barrier_nospec(!!val);
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return 0;
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}
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static int barrier_nospec_get(void *data, u64 *val)
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{
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*val = barrier_nospec_enabled ? 1 : 0;
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return 0;
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}
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DEFINE_SIMPLE_ATTRIBUTE(fops_barrier_nospec,
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barrier_nospec_get, barrier_nospec_set, "%llu\n");
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static __init int barrier_nospec_debugfs_init(void)
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{
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debugfs_create_file("barrier_nospec", 0600, powerpc_debugfs_root, NULL,
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&fops_barrier_nospec);
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return 0;
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}
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device_initcall(barrier_nospec_debugfs_init);
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static __init int security_feature_debugfs_init(void)
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{
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debugfs_create_x64("security_features", 0400, powerpc_debugfs_root,
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(u64 *)&powerpc_security_features);
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return 0;
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}
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device_initcall(security_feature_debugfs_init);
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#endif /* CONFIG_DEBUG_FS */
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#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
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static int __init handle_nospectre_v2(char *p)
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{
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no_spectrev2 = true;
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return 0;
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}
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early_param("nospectre_v2", handle_nospectre_v2);
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#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */
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#ifdef CONFIG_PPC_FSL_BOOK3E
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void setup_spectre_v2(void)
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{
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if (no_spectrev2 || cpu_mitigations_off())
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do_btb_flush_fixups();
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else
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btb_flush_enabled = true;
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}
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#endif /* CONFIG_PPC_FSL_BOOK3E */
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#ifdef CONFIG_PPC_BOOK3S_64
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ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
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{
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bool thread_priv;
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thread_priv = security_ftr_enabled(SEC_FTR_L1D_THREAD_PRIV);
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if (rfi_flush || thread_priv) {
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struct seq_buf s;
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seq_buf_init(&s, buf, PAGE_SIZE - 1);
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seq_buf_printf(&s, "Mitigation: ");
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if (rfi_flush)
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seq_buf_printf(&s, "RFI Flush");
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if (rfi_flush && thread_priv)
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seq_buf_printf(&s, ", ");
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if (thread_priv)
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seq_buf_printf(&s, "L1D private per thread");
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seq_buf_printf(&s, "\n");
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return s.len;
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}
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if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
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!security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
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return sprintf(buf, "Not affected\n");
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return sprintf(buf, "Vulnerable\n");
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}
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#endif
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ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf)
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{
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struct seq_buf s;
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seq_buf_init(&s, buf, PAGE_SIZE - 1);
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if (security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR)) {
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if (barrier_nospec_enabled)
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seq_buf_printf(&s, "Mitigation: __user pointer sanitization");
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else
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seq_buf_printf(&s, "Vulnerable");
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if (security_ftr_enabled(SEC_FTR_SPEC_BAR_ORI31))
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seq_buf_printf(&s, ", ori31 speculation barrier enabled");
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seq_buf_printf(&s, "\n");
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} else
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seq_buf_printf(&s, "Not affected\n");
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return s.len;
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}
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ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
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{
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struct seq_buf s;
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bool bcs, ccd;
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seq_buf_init(&s, buf, PAGE_SIZE - 1);
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bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
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ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
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if (bcs || ccd) {
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seq_buf_printf(&s, "Mitigation: ");
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if (bcs)
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seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");
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if (bcs && ccd)
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seq_buf_printf(&s, ", ");
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if (ccd)
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seq_buf_printf(&s, "Indirect branch cache disabled");
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if (link_stack_flush_enabled)
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seq_buf_printf(&s, ", Software link stack flush");
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} else if (count_cache_flush_type != COUNT_CACHE_FLUSH_NONE) {
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seq_buf_printf(&s, "Mitigation: Software count cache flush");
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if (count_cache_flush_type == COUNT_CACHE_FLUSH_HW)
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seq_buf_printf(&s, " (hardware accelerated)");
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if (link_stack_flush_enabled)
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seq_buf_printf(&s, ", Software link stack flush");
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} else if (btb_flush_enabled) {
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seq_buf_printf(&s, "Mitigation: Branch predictor state flush");
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} else {
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seq_buf_printf(&s, "Vulnerable");
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}
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seq_buf_printf(&s, "\n");
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return s.len;
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}
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#ifdef CONFIG_PPC_BOOK3S_64
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/*
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* Store-forwarding barrier support.
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*/
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static enum stf_barrier_type stf_enabled_flush_types;
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static bool no_stf_barrier;
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bool stf_barrier;
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static int __init handle_no_stf_barrier(char *p)
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{
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pr_info("stf-barrier: disabled on command line.");
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no_stf_barrier = true;
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return 0;
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}
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early_param("no_stf_barrier", handle_no_stf_barrier);
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/* This is the generic flag used by other architectures */
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static int __init handle_ssbd(char *p)
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{
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if (!p || strncmp(p, "auto", 5) == 0 || strncmp(p, "on", 2) == 0 ) {
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/* Until firmware tells us, we have the barrier with auto */
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return 0;
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} else if (strncmp(p, "off", 3) == 0) {
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handle_no_stf_barrier(NULL);
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return 0;
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} else
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return 1;
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return 0;
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}
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early_param("spec_store_bypass_disable", handle_ssbd);
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/* This is the generic flag used by other architectures */
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static int __init handle_no_ssbd(char *p)
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{
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handle_no_stf_barrier(NULL);
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return 0;
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}
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early_param("nospec_store_bypass_disable", handle_no_ssbd);
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static void stf_barrier_enable(bool enable)
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{
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if (enable)
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do_stf_barrier_fixups(stf_enabled_flush_types);
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else
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do_stf_barrier_fixups(STF_BARRIER_NONE);
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stf_barrier = enable;
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}
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void setup_stf_barrier(void)
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{
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enum stf_barrier_type type;
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bool enable, hv;
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hv = cpu_has_feature(CPU_FTR_HVMODE);
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/* Default to fallback in case fw-features are not available */
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if (cpu_has_feature(CPU_FTR_ARCH_300))
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type = STF_BARRIER_EIEIO;
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else if (cpu_has_feature(CPU_FTR_ARCH_207S))
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type = STF_BARRIER_SYNC_ORI;
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else if (cpu_has_feature(CPU_FTR_ARCH_206))
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type = STF_BARRIER_FALLBACK;
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else
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type = STF_BARRIER_NONE;
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enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
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(security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR) ||
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(security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) && hv));
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if (type == STF_BARRIER_FALLBACK) {
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pr_info("stf-barrier: fallback barrier available\n");
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} else if (type == STF_BARRIER_SYNC_ORI) {
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pr_info("stf-barrier: hwsync barrier available\n");
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} else if (type == STF_BARRIER_EIEIO) {
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pr_info("stf-barrier: eieio barrier available\n");
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}
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stf_enabled_flush_types = type;
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if (!no_stf_barrier && !cpu_mitigations_off())
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stf_barrier_enable(enable);
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}
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ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
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{
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if (stf_barrier && stf_enabled_flush_types != STF_BARRIER_NONE) {
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const char *type;
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switch (stf_enabled_flush_types) {
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case STF_BARRIER_EIEIO:
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type = "eieio";
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break;
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case STF_BARRIER_SYNC_ORI:
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type = "hwsync";
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break;
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case STF_BARRIER_FALLBACK:
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type = "fallback";
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break;
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default:
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type = "unknown";
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}
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return sprintf(buf, "Mitigation: Kernel entry/exit barrier (%s)\n", type);
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}
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if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
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!security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
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return sprintf(buf, "Not affected\n");
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return sprintf(buf, "Vulnerable\n");
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}
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#ifdef CONFIG_DEBUG_FS
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static int stf_barrier_set(void *data, u64 val)
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{
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bool enable;
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if (val == 1)
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enable = true;
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else if (val == 0)
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enable = false;
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else
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return -EINVAL;
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/* Only do anything if we're changing state */
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if (enable != stf_barrier)
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stf_barrier_enable(enable);
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return 0;
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}
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static int stf_barrier_get(void *data, u64 *val)
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{
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*val = stf_barrier ? 1 : 0;
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return 0;
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}
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DEFINE_SIMPLE_ATTRIBUTE(fops_stf_barrier, stf_barrier_get, stf_barrier_set, "%llu\n");
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static __init int stf_barrier_debugfs_init(void)
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{
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debugfs_create_file("stf_barrier", 0600, powerpc_debugfs_root, NULL, &fops_stf_barrier);
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return 0;
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}
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device_initcall(stf_barrier_debugfs_init);
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#endif /* CONFIG_DEBUG_FS */
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static void no_count_cache_flush(void)
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{
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count_cache_flush_type = COUNT_CACHE_FLUSH_NONE;
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pr_info("count-cache-flush: software flush disabled.\n");
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}
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static void toggle_count_cache_flush(bool enable)
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{
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if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE) &&
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!security_ftr_enabled(SEC_FTR_FLUSH_LINK_STACK))
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enable = false;
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if (!enable) {
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patch_instruction_site(&patch__call_flush_count_cache, PPC_INST_NOP);
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#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
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patch_instruction_site(&patch__call_kvm_flush_link_stack, PPC_INST_NOP);
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#endif
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pr_info("link-stack-flush: software flush disabled.\n");
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link_stack_flush_enabled = false;
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no_count_cache_flush();
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return;
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}
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// This enables the branch from _switch to flush_count_cache
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patch_branch_site(&patch__call_flush_count_cache,
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(u64)&flush_count_cache, BRANCH_SET_LINK);
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#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
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// This enables the branch from guest_exit_cont to kvm_flush_link_stack
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patch_branch_site(&patch__call_kvm_flush_link_stack,
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(u64)&kvm_flush_link_stack, BRANCH_SET_LINK);
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#endif
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pr_info("link-stack-flush: software flush enabled.\n");
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link_stack_flush_enabled = true;
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// If we just need to flush the link stack, patch an early return
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if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE)) {
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patch_instruction_site(&patch__flush_link_stack_return, PPC_INST_BLR);
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no_count_cache_flush();
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return;
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}
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if (!security_ftr_enabled(SEC_FTR_BCCTR_FLUSH_ASSIST)) {
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count_cache_flush_type = COUNT_CACHE_FLUSH_SW;
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pr_info("count-cache-flush: full software flush sequence enabled.\n");
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return;
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}
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patch_instruction_site(&patch__flush_count_cache_return, PPC_INST_BLR);
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count_cache_flush_type = COUNT_CACHE_FLUSH_HW;
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pr_info("count-cache-flush: hardware assisted flush sequence enabled\n");
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}
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void setup_count_cache_flush(void)
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{
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bool enable = true;
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if (no_spectrev2 || cpu_mitigations_off()) {
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if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) ||
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security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED))
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pr_warn("Spectre v2 mitigations not fully under software control, can't disable\n");
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enable = false;
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}
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/*
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* There's no firmware feature flag/hypervisor bit to tell us we need to
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* flush the link stack on context switch. So we set it here if we see
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* either of the Spectre v2 mitigations that aim to protect userspace.
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*/
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if (security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED) ||
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security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE))
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security_ftr_set(SEC_FTR_FLUSH_LINK_STACK);
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toggle_count_cache_flush(enable);
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}
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#ifdef CONFIG_DEBUG_FS
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static int count_cache_flush_set(void *data, u64 val)
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{
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bool enable;
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if (val == 1)
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enable = true;
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else if (val == 0)
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enable = false;
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else
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return -EINVAL;
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toggle_count_cache_flush(enable);
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return 0;
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}
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static int count_cache_flush_get(void *data, u64 *val)
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{
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if (count_cache_flush_type == COUNT_CACHE_FLUSH_NONE)
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*val = 0;
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else
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*val = 1;
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return 0;
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}
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DEFINE_SIMPLE_ATTRIBUTE(fops_count_cache_flush, count_cache_flush_get,
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count_cache_flush_set, "%llu\n");
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static __init int count_cache_flush_debugfs_init(void)
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{
|
|
debugfs_create_file("count_cache_flush", 0600, powerpc_debugfs_root,
|
|
NULL, &fops_count_cache_flush);
|
|
return 0;
|
|
}
|
|
device_initcall(count_cache_flush_debugfs_init);
|
|
#endif /* CONFIG_DEBUG_FS */
|
|
#endif /* CONFIG_PPC_BOOK3S_64 */
|