[RFC PATCH v4 6/9] x86/cet/ibt: Add arch_prctl functions for IBT

[Yu-cheng Yu]

Update ARCH_CET_STATUS and ARCH_CET_DISABLE to include Indirect
Branch Tracking features.

Introduce:

arch_prctl(ARCH_CET_LEGACY_BITMAP, unsigned long *addr)
    Enable the Indirect Branch Tracking legacy code bitmap.

    The parameter 'addr' is a pointer to a user buffer.
    On returning to the caller, the kernel fills the following:

    *addr = IBT bitmap base address
    *(addr + 1) = IBT bitmap size

Signed-off-by: H.J. Lu <hjl.to...@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng...@intel.com>
---
 arch/x86/include/uapi/asm/prctl.h |  1 +
 arch/x86/kernel/cet_prctl.c       | 38 ++++++++++++++++++++++++++++++-
 arch/x86/kernel/process.c         |  1 +
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/prctl.h 
b/arch/x86/include/uapi/asm/prctl.h
index 3aec1088e01d..31d2465f9caf 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -18,5 +18,6 @@
 #define ARCH_CET_DISABLE       0x3002
 #define ARCH_CET_LOCK          0x3003
 #define ARCH_CET_ALLOC_SHSTK   0x3004
+#define ARCH_CET_LEGACY_BITMAP 0x3005
 
 #endif /* _ASM_X86_PRCTL_H */
diff --git a/arch/x86/kernel/cet_prctl.c b/arch/x86/kernel/cet_prctl.c
index c4b7c19f5040..df47b5ebc3f4 100644
--- a/arch/x86/kernel/cet_prctl.c
+++ b/arch/x86/kernel/cet_prctl.c
@@ -20,6 +20,8 @@ static int handle_get_status(unsigned long arg2)
 
        if (current->thread.cet.shstk_enabled)
                features |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
+       if (current->thread.cet.ibt_enabled)
+               features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
 
        shstk_base = current->thread.cet.shstk_base;
        shstk_size = current->thread.cet.shstk_size;
@@ -49,9 +51,35 @@ static int handle_alloc_shstk(unsigned long arg2)
        return 0;
 }
 
+static int handle_bitmap(unsigned long arg2)
+{
+       unsigned long addr, size;
+
+       if (current->thread.cet.ibt_enabled) {
+               int err;
+
+               err  = cet_setup_ibt_bitmap();
+               if (err)
+                       return err;
+
+               addr = current->thread.cet.ibt_bitmap_addr;
+               size = current->thread.cet.ibt_bitmap_size;
+       } else {
+               addr = 0;
+               size = 0;
+       }
+
+       if (put_user(addr, (unsigned long __user *)arg2) ||
+           put_user(size, (unsigned long __user *)arg2 + 1))
+               return -EFAULT;
+
+       return 0;
+}
+
 int prctl_cet(int option, unsigned long arg2)
 {
-       if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+       if (!cpu_feature_enabled(X86_FEATURE_SHSTK) &&
+           !cpu_feature_enabled(X86_FEATURE_IBT))
                return -EINVAL;
 
        switch (option) {
@@ -63,6 +91,8 @@ int prctl_cet(int option, unsigned long arg2)
                        return -EPERM;
                if (arg2 & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
                        cet_disable_free_shstk(current);
+               if (arg2 & GNU_PROPERTY_X86_FEATURE_1_IBT)
+                       cet_disable_ibt();
 
                return 0;
 
@@ -73,6 +103,12 @@ int prctl_cet(int option, unsigned long arg2)
        case ARCH_CET_ALLOC_SHSTK:
                return handle_alloc_shstk(arg2);
 
+       /*
+        * Allocate legacy bitmap and return address & size to user.
+        */
+       case ARCH_CET_LEGACY_BITMAP:
+               return handle_bitmap(arg2);
+
        default:
                return -EINVAL;
        }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ac0ea9c7e89f..aea15a9b6a3e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -797,6 +797,7 @@ long do_arch_prctl_common(struct task_struct *task, int 
option,
        case ARCH_CET_DISABLE:
        case ARCH_CET_LOCK:
        case ARCH_CET_ALLOC_SHSTK:
+       case ARCH_CET_LEGACY_BITMAP:
                return prctl_cet(option, cpuid_enabled);
        }
 
-- 
2.17.1