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Subject[RFC PATCH v2 22/27] x86/cet/ibt: User-mode indirect branch tracking support
Date
Add user-mode indirect branch tracking enabling/disabling
and supporting routines.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/cet.h | 8 +++
arch/x86/include/asm/disabled-features.h | 8 ++-
arch/x86/kernel/cet.c | 73 ++++++++++++++++++++++++
arch/x86/kernel/cpu/common.c | 20 ++++++-
arch/x86/kernel/elf.c | 16 +++++-
arch/x86/kernel/process.c | 1 +
6 files changed, 123 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index d9ae3d86cdd7..71da2cccba16 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -12,7 +12,10 @@ struct task_struct;
struct cet_status {
unsigned long shstk_base;
unsigned long shstk_size;
+ unsigned long ibt_bitmap_addr;
+ unsigned long ibt_bitmap_size;
unsigned int shstk_enabled:1;
+ unsigned int ibt_enabled:1;
};

#ifdef CONFIG_X86_INTEL_CET
@@ -21,6 +24,9 @@ void cet_disable_shstk(void);
void cet_disable_free_shstk(struct task_struct *p);
int cet_restore_signal(unsigned long ssp);
int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp);
+int cet_setup_ibt(void);
+int cet_setup_ibt_bitmap(void);
+void cet_disable_ibt(void);
#else
static inline int cet_setup_shstk(void) { return 0; }
static inline void cet_disable_shstk(void) {}
@@ -28,6 +34,8 @@ static inline void cet_disable_free_shstk(struct task_struct *p) {}
static inline int cet_restore_signal(unsigned long ssp) { return 0; }
static inline int cet_setup_signal(bool ia32, unsigned long rstor,
unsigned long *new_ssp) { return 0; }
+static inline int cet_setup_ibt(void) { return 0; }
+static inline void cet_disable_ibt(void) {}
#endif

#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 3624a11e5ba6..ce5bdaf0f1ff 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -62,6 +62,12 @@
#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31))
#endif

+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+#define DISABLE_IBT 0
+#else
+#define DISABLE_IBT (1<<(X86_FEATURE_IBT & 31))
+#endif
+
/*
* Make sure to add features to the correct mask
*/
@@ -72,7 +78,7 @@
#define DISABLED_MASK4 (DISABLE_PCID)
#define DISABLED_MASK5 0
#define DISABLED_MASK6 0
-#define DISABLED_MASK7 (DISABLE_PTI)
+#define DISABLED_MASK7 (DISABLE_PTI|DISABLE_IBT)
#define DISABLED_MASK8 0
#define DISABLED_MASK9 (DISABLE_MPX)
#define DISABLED_MASK10 0
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index 4eba7790c4e4..8bbd63e1a2ba 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -12,6 +12,8 @@
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/sched/signal.h>
+#include <linux/vmalloc.h>
+#include <linux/bitops.h>
#include <asm/msr.h>
#include <asm/user.h>
#include <asm/fpu/xstate.h>
@@ -241,3 +243,74 @@ int cet_setup_signal(bool ia32, unsigned long rstor_addr,
set_shstk_ptr(ssp);
return 0;
}
+
+static unsigned long ibt_mmap(unsigned long addr, unsigned long len)
+{
+ struct mm_struct *mm = current->mm;
+ unsigned long populate;
+
+ down_write(&mm->mmap_sem);
+ addr = do_mmap(NULL, addr, len, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE,
+ VM_DONTDUMP, 0, &populate, NULL);
+ up_write(&mm->mmap_sem);
+
+ if (populate)
+ mm_populate(addr, populate);
+
+ return addr;
+}
+
+int cet_setup_ibt(void)
+{
+ u64 r;
+
+ if (!cpu_feature_enabled(X86_FEATURE_IBT))
+ return -EOPNOTSUPP;
+
+ rdmsrl(MSR_IA32_U_CET, r);
+ r |= (MSR_IA32_CET_ENDBR_EN | MSR_IA32_CET_NO_TRACK_EN);
+ wrmsrl(MSR_IA32_U_CET, r);
+ current->thread.cet.ibt_enabled = 1;
+ return 0;
+}
+
+int cet_setup_ibt_bitmap(void)
+{
+ u64 r;
+ unsigned long bitmap;
+ unsigned long size;
+
+ if (!cpu_feature_enabled(X86_FEATURE_IBT))
+ return -EOPNOTSUPP;
+
+ size = TASK_SIZE_MAX / PAGE_SIZE / BITS_PER_BYTE;
+ bitmap = ibt_mmap(0, size);
+
+ if (bitmap >= TASK_SIZE_MAX)
+ return -ENOMEM;
+
+ bitmap &= PAGE_MASK;
+
+ rdmsrl(MSR_IA32_U_CET, r);
+ r |= (MSR_IA32_CET_LEG_IW_EN | bitmap);
+ wrmsrl(MSR_IA32_U_CET, r);
+
+ current->thread.cet.ibt_bitmap_addr = bitmap;
+ current->thread.cet.ibt_bitmap_size = size;
+ return 0;
+}
+
+void cet_disable_ibt(void)
+{
+ u64 r;
+
+ if (!cpu_feature_enabled(X86_FEATURE_IBT))
+ return;
+
+ rdmsrl(MSR_IA32_U_CET, r);
+ r &= ~(MSR_IA32_CET_ENDBR_EN | MSR_IA32_CET_LEG_IW_EN |
+ MSR_IA32_CET_NO_TRACK_EN);
+ wrmsrl(MSR_IA32_U_CET, r);
+ current->thread.cet.ibt_enabled = 0;
+}
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 705467839ce8..c609c9ce5691 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -413,7 +413,8 @@ __setup("nopku", setup_disable_pku);

static __always_inline void setup_cet(struct cpuinfo_x86 *c)
{
- if (cpu_feature_enabled(X86_FEATURE_SHSTK))
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) ||
+ cpu_feature_enabled(X86_FEATURE_IBT))
cr4_set_bits(X86_CR4_CET);
}

@@ -434,6 +435,23 @@ static __init int setup_disable_shstk(char *s)
__setup("no_cet_shstk", setup_disable_shstk);
#endif

+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+static __init int setup_disable_ibt(char *s)
+{
+ /* require an exact match without trailing characters */
+ if (strlen(s))
+ return 0;
+
+ if (!boot_cpu_has(X86_FEATURE_IBT))
+ return 1;
+
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+ pr_info("x86: 'no_cet_ibt' specified, disabling Branch Tracking\n");
+ return 1;
+}
+__setup("no_cet_ibt", setup_disable_ibt);
+#endif
+
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c
index 233f6dad9c1f..42e08d3b573e 100644
--- a/arch/x86/kernel/elf.c
+++ b/arch/x86/kernel/elf.c
@@ -15,6 +15,7 @@
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/string.h>
+#include <linux/compat.h>

/*
* The .note.gnu.property layout:
@@ -222,7 +223,8 @@ int arch_setup_features(void *ehdr_p, void *phdr_p,

struct elf64_hdr *ehdr64 = ehdr_p;

- if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK) &&
+ !cpu_feature_enabled(X86_FEATURE_IBT))
return 0;

if (ehdr64->e_ident[EI_CLASS] == ELFCLASS64) {
@@ -250,6 +252,9 @@ int arch_setup_features(void *ehdr_p, void *phdr_p,
current->thread.cet.shstk_enabled = 0;
current->thread.cet.shstk_base = 0;
current->thread.cet.shstk_size = 0;
+ current->thread.cet.ibt_enabled = 0;
+ current->thread.cet.ibt_bitmap_addr = 0;
+ current->thread.cet.ibt_bitmap_size = 0;
if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
if (shstk) {
err = cet_setup_shstk();
@@ -257,6 +262,15 @@ int arch_setup_features(void *ehdr_p, void *phdr_p,
goto out;
}
}
+
+ if (cpu_feature_enabled(X86_FEATURE_IBT)) {
+ if (ibt) {
+ err = cet_setup_ibt();
+ if (err < 0)
+ goto out;
+ }
+ }
+
out:
return err;
}
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b3b0b482983a..309ebb7f9d8d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -138,6 +138,7 @@ void flush_thread(void)
memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));

cet_disable_shstk();
+ cet_disable_ibt();
fpu__clear(&tsk->thread.fpu);
}

--
2.17.1
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