[PATCH v3 22/39] x86/ibt: Add IBT feature, MSR and #CP handling

Peter Zijlstra
2022-03-03T11:31:57Z

The bits required to make the hardware go.. Of note is that, provided
the syscall entry points are covered with ENDBR, #CP doesn't need to
be an IST because we'll never hit the syscall gap.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/cpu.h | 4 +
arch/x86/include/asm/cpufeatures.h | 1
arch/x86/include/asm/idtentry.h | 5 ++
arch/x86/include/asm/msr-index.h | 20 ++++++++-
arch/x86/include/asm/traps.h | 2
arch/x86/include/uapi/asm/processor-flags.h | 2
arch/x86/kernel/cpu/common.c | 31 +++++++++++++-
arch/x86/kernel/idt.c | 4 +
arch/x86/kernel/machine_kexec_64.c | 2
arch/x86/kernel/relocate_kernel_64.S | 8 +++
arch/x86/kernel/traps.c | 61 ++++++++++++++++++++++++++++
11 files changed, 138 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -7,6 +7,7 @@
#include <linux/topology.h>
#include <linux/nodemask.h>
#include <linux/percpu.h>
+#include <asm/ibt.h>

#ifdef CONFIG_SMP

@@ -72,4 +73,7 @@ void init_ia32_feat_ctl(struct cpuinfo_x
#else
static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
#endif
+
+extern __noendbr void cet_disable(void);
+
#endif /* _ASM_X86_CPU_H */
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -387,6 +387,7 @@
#define X86_FEATURE_TSXLDTRK (18*32+16) /* TSX Suspend Load Address Tracking */
#define X86_FEATURE_PCONFIG (18*32+18) /* Intel PCONFIG */
#define X86_FEATURE_ARCH_LBR (18*32+19) /* Intel ARCH LBR */
+#define X86_FEATURE_IBT (18*32+20) /* Indirect Branch Tracking */
#define X86_FEATURE_AMX_BF16 (18*32+22) /* AMX bf16 Support */
#define X86_FEATURE_AVX512_FP16 (18*32+23) /* AVX512 FP16 */
#define X86_FEATURE_AMX_TILE (18*32+24) /* AMX tile Support */
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -617,6 +617,11 @@ DECLARE_IDTENTRY_DF(X86_TRAP_DF, exc_dou
DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_DF, xenpv_exc_double_fault);
#endif

+/* #CP */
+#ifdef CONFIG_X86_KERNEL_IBT
+DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_CP, exc_control_protection);
+#endif
+
/* #VC */
#ifdef CONFIG_AMD_MEM_ENCRYPT
DECLARE_IDTENTRY_VC(X86_TRAP_VC, exc_vmm_communication);
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -362,11 +362,29 @@
#define MSR_ATOM_CORE_TURBO_RATIOS 0x0000066c
#define MSR_ATOM_CORE_TURBO_VIDS 0x0000066d

-
#define MSR_CORE_PERF_LIMIT_REASONS 0x00000690
#define MSR_GFX_PERF_LIMIT_REASONS 0x000006B0
#define MSR_RING_PERF_LIMIT_REASONS 0x000006B1

+/* Control-flow Enforcement Technology MSRs */
+#define MSR_IA32_U_CET 0x000006a0 /* user mode cet */
+#define MSR_IA32_S_CET 0x000006a2 /* kernel mode cet */
+#define CET_SHSTK_EN BIT_ULL(0)
+#define CET_WRSS_EN BIT_ULL(1)
+#define CET_ENDBR_EN BIT_ULL(2)
+#define CET_LEG_IW_EN BIT_ULL(3)
+#define CET_NO_TRACK_EN BIT_ULL(4)
+#define CET_SUPPRESS_DISABLE BIT_ULL(5)
+#define CET_RESERVED (BIT_ULL(6) | BIT_ULL(7) | BIT_ULL(8) | BIT_ULL(9))
+#define CET_SUPPRESS BIT_ULL(10)
+#define CET_WAIT_ENDBR BIT_ULL(11)
+
+#define MSR_IA32_PL0_SSP 0x000006a4 /* ring-0 shadow stack pointer */
+#define MSR_IA32_PL1_SSP 0x000006a5 /* ring-1 shadow stack pointer */
+#define MSR_IA32_PL2_SSP 0x000006a6 /* ring-2 shadow stack pointer */
+#define MSR_IA32_PL3_SSP 0x000006a7 /* ring-3 shadow stack pointer */
+#define MSR_IA32_INT_SSP_TAB 0x000006a8 /* exception shadow stack table */
+
/* Hardware P state interface */
#define MSR_PPERF 0x0000064e
#define MSR_PERF_LIMIT_REASONS 0x0000064f
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -18,6 +18,8 @@ void __init trap_init(void);
asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *eregs);
#endif

+extern bool ibt_selftest(void);
+
#ifdef CONFIG_X86_F00F_BUG
/* For handling the FOOF bug */
void handle_invalid_op(struct pt_regs *regs);
--- a/arch/x86/include/uapi/asm/processor-flags.h
+++ b/arch/x86/include/uapi/asm/processor-flags.h
@@ -130,6 +130,8 @@
#define X86_CR4_SMAP _BITUL(X86_CR4_SMAP_BIT)
#define X86_CR4_PKE_BIT 22 /* enable Protection Keys support */
#define X86_CR4_PKE _BITUL(X86_CR4_PKE_BIT)
+#define X86_CR4_CET_BIT 23 /* enable Control-flow Enforcement Technology */
+#define X86_CR4_CET _BITUL(X86_CR4_CET_BIT)

/*
* x86-64 Task Priority Register, CR8
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -59,6 +59,7 @@
#include <asm/cpu_device_id.h>
#include <asm/uv/uv.h>
#include <asm/sigframe.h>
+#include <asm/traps.h>

#include "cpu.h"

@@ -438,7 +439,8 @@ static __always_inline void setup_umip(s

/* These bits should not change their value after CPU init is finished. */
static const unsigned long cr4_pinned_mask =
- X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP | X86_CR4_FSGSBASE;
+ X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
+ X86_CR4_FSGSBASE | X86_CR4_CET;
static DEFINE_STATIC_KEY_FALSE_RO(cr_pinning);
static unsigned long cr4_pinned_bits __ro_after_init;

@@ -592,6 +594,30 @@ static __init int setup_disable_pku(char
__setup("nopku", setup_disable_pku);
#endif /* CONFIG_X86_64 */

+static __always_inline void setup_cet(struct cpuinfo_x86 *c)
+{
+ u64 msr = CET_ENDBR_EN;
+
+ if (!HAS_KERNEL_IBT ||
+ !cpu_feature_enabled(X86_FEATURE_IBT))
+ return;
+
+ wrmsrl(MSR_IA32_S_CET, msr);
+ cr4_set_bits(X86_CR4_CET);
+
+ if (!ibt_selftest()) {
+ pr_err("IBT selftest: Failed!\n");
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+ return;
+ }
+}
+
+__noendbr void cet_disable(void)
+{
+ if (cpu_feature_enabled(X86_FEATURE_IBT))
+ wrmsrl(MSR_IA32_S_CET, 0);
+}
+
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
@@ -1709,6 +1735,7 @@ static void identify_cpu(struct cpuinfo_

x86_init_rdrand(c);
setup_pku(c);
+ setup_cet(c);

/*
* Clear/Set all flags overridden by options, need do it
@@ -1777,6 +1804,8 @@ void enable_sep_cpu(void)
void __init identify_boot_cpu(void)
{
identify_cpu(&boot_cpu_data);
+ if (HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT))
+ pr_info("CET detected: Indirect Branch Tracking enabled\n");
#ifdef CONFIG_X86_32
sysenter_setup();
enable_sep_cpu();
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -104,6 +104,10 @@ static const __initconst struct idt_data
ISTG(X86_TRAP_MC, asm_exc_machine_check, IST_INDEX_MCE),
#endif

+#ifdef CONFIG_X86_KERNEL_IBT
+ INTG(X86_TRAP_CP, asm_exc_control_protection),
+#endif
+
#ifdef CONFIG_AMD_MEM_ENCRYPT
ISTG(X86_TRAP_VC, asm_exc_vmm_communication, IST_INDEX_VC),
#endif
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -27,6 +27,7 @@
#include <asm/kexec-bzimage64.h>
#include <asm/setup.h>
#include <asm/set_memory.h>
+#include <asm/cpu.h>

#ifdef CONFIG_ACPI
/*
@@ -310,6 +311,7 @@ void machine_kexec(struct kimage *image)
/* Interrupts aren't acceptable while we reboot */
local_irq_disable();
hw_breakpoint_disable();
+ cet_disable();

if (image->preserve_context) {
#ifdef CONFIG_X86_IO_APIC
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -115,6 +115,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_ma
pushq %rdx

/*
+ * Clear X86_CR4_CET (if it was set) such that we can clear CR0_WP
+ * below.
+ */
+ movq %cr4, %rax
+ andq $~(X86_CR4_CET), %rax
+ movq %rax, %cr4
+
+ /*
* Set cr0 to a known state:
* - Paging enabled
* - Alignment check disabled
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -210,6 +210,67 @@ DEFINE_IDTENTRY(exc_overflow)
do_error_trap(regs, 0, "overflow", X86_TRAP_OF, SIGSEGV, 0, NULL);
}

+#ifdef CONFIG_X86_KERNEL_IBT
+
+static __ro_after_init bool ibt_fatal = true;
+
+void ibt_selftest_ip(void); /* code label defined in asm below */
+
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+ if (!cpu_feature_enabled(X86_FEATURE_IBT)) {
+ pr_err("Unexpected #CP\n");
+ BUG();
+ }
+
+ if (WARN_ON_ONCE(user_mode(regs) || error_code != 3))
+ return;
+
+ if (unlikely(regs->ip == (unsigned long)ibt_selftest_ip)) {
+ regs->ax = 0;
+ return;
+ }
+
+ pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
+ if (!ibt_fatal) {
+ printk(KERN_DEFAULT CUT_HERE);
+ __warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);
+ return;
+ }
+ BUG();
+}
+
+bool ibt_selftest(void)
+{
+ unsigned long ret;
+
+ asm (" lea ibt_selftest_ip(%%rip), %%rax\n\t"
+ ANNOTATE_RETPOLINE_SAFE
+ " jmp *%%rax\n\t"
+ ASM_REACHABLE
+ ANNOTATE_NOENDBR
+ "ibt_selftest_ip: nop\n\t"
+
+ : "=a" (ret) : : "memory");
+
+ return !ret;
+}
+
+static int __init ibt_setup(char *str)
+{
+ if (!strcmp(str, "off"))
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+
+ if (!strcmp(str, "warn"))
+ ibt_fatal = false;
+
+ return 1;
+}
+
+__setup("ibt=", ibt_setup);
+
+#endif /* CONFIG_X86_KERNEL_IBT */
+
#ifdef CONFIG_X86_F00F_BUG
void handle_invalid_op(struct pt_regs *regs)
#else