[PATCH v23 04/28] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions

Yu-cheng Yu
2021-03-16T15:12:28Z

Introduce a software-defined X86_FEATURE_CET, which indicates either Shadow
Stack or Indirect Branch Tracking (or both) is present. Also introduce
related cpu init/setup functions.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
arch/x86/include/asm/cpufeatures.h | 2 +-
arch/x86/include/asm/disabled-features.h | 5 ++++-
arch/x86/include/uapi/asm/processor-flags.h | 2 ++
arch/x86/kernel/cpu/common.c | 14 ++++++++++++++
arch/x86/kernel/cpu/intel.c | 3 +++
5 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index bf861fc89fef..d771e62677de 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -108,7 +108,7 @@
#define X86_FEATURE_EXTD_APICID ( 3*32+26) /* Extended APICID (8 bits) */
#define X86_FEATURE_AMD_DCM ( 3*32+27) /* AMD multi-node processor */
#define X86_FEATURE_APERFMPERF ( 3*32+28) /* P-State hardware coordination feedback capability (APERF/MPERF MSRs) */
-/* free ( 3*32+29) */
+#define X86_FEATURE_CET ( 3*32+29) /* Control-flow enforcement */
#define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
#define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */

diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 914b353fe75c..b9a73b882cf9 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -71,9 +71,11 @@
#ifdef CONFIG_X86_CET
#define DISABLE_SHSTK 0
#define DISABLE_IBT 0
+#define DISABLE_CET 0
#else
#define DISABLE_SHSTK (1 << (X86_FEATURE_SHSTK & 31))
#define DISABLE_IBT (1 << (X86_FEATURE_IBT & 31))
+#define DISABLE_CET (1 << (X86_FEATURE_CET & 31))
#endif

/*
@@ -82,7 +84,8 @@
#define DISABLED_MASK0 (DISABLE_VME)
#define DISABLED_MASK1 0
#define DISABLED_MASK2 0
-#define DISABLED_MASK3 (DISABLE_CYRIX_ARR|DISABLE_CENTAUR_MCR|DISABLE_K6_MTRR)
+#define DISABLED_MASK3 (DISABLE_CYRIX_ARR|DISABLE_CENTAUR_MCR|DISABLE_K6_MTRR| \
+ DISABLE_CET)
#define DISABLED_MASK4 (DISABLE_PCID)
#define DISABLED_MASK5 0
#define DISABLED_MASK6 0
diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
index bcba3c643e63..a8df907e8017 100644
--- 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 */
+#define X86_CR4_CET _BITUL(X86_CR4_CET_BIT)

/*
* x86-64 Task Priority Register, CR8
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index ab640abe26b6..6bd07727089e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -510,6 +510,14 @@ static __init int setup_disable_pku(char *arg)
__setup("nopku", setup_disable_pku);
#endif /* CONFIG_X86_64 */

+static __always_inline void setup_cet(struct cpuinfo_x86 *c)
+{
+ if (!cpu_feature_enabled(X86_FEATURE_CET))
+ return;
+
+ cr4_set_bits(X86_CR4_CET);
+}
+
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
@@ -1255,6 +1263,11 @@ static void __init cpu_parse_early_param(void)
if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
setup_clear_cpu_cap(X86_FEATURE_XSAVES);

+ if (cmdline_find_option_bool(boot_command_line, "no_user_shstk"))
+ setup_clear_cpu_cap(X86_FEATURE_SHSTK);
+ if (cmdline_find_option_bool(boot_command_line, "no_user_ibt"))
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+
arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
if (arglen <= 0)
return;
@@ -1594,6 +1607,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)

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

/*
* Clear/Set all flags overridden by options, need do it
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 0e422a544835..2e11d9555e9b 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -334,6 +334,9 @@ static void early_init_intel(struct cpuinfo_x86 *c)

static void bsp_init_intel(struct cpuinfo_x86 *c)
{
+ if (cpu_has(c, X86_FEATURE_SHSTK) || cpu_has(c, X86_FEATURE_IBT))
+ setup_force_cpu_cap(X86_FEATURE_CET);
+
resctrl_cpu_detect(c);
}

--
2.21.0