x86/mm: Provide arch_prctl() interface for LAM

Add a few of arch_prctl() handles:

 - ARCH_ENABLE_TAGGED_ADDR enabled LAM. The argument is required number
   of tag bits. It is rounded up to the nearest LAM mode that can
   provide it. For now only LAM_U57 is supported, with 6 tag bits.

 - ARCH_GET_UNTAG_MASK returns untag mask. It can indicates where tag
   bits located in the address.

 - ARCH_GET_MAX_TAG_BITS returns the maximum tag bits user can request.
   Zero if LAM is not supported.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/all/20230312112612.31869-9-kirill.shutemov%40linux.intel.com

diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 9cac8c4..e80762e 100644 (file)
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -12,6 +12,8 @@
 #define MM_CONTEXT_UPROBE_IA32         0
 /* vsyscall page is accessible on this MM */
 #define MM_CONTEXT_HAS_VSYSCALL                1
+/* Do not allow changing LAM mode */
+#define MM_CONTEXT_LOCK_LAM            2
 
 /*
  * x86 has arch-specific MMU state beyond what lives in mm_struct.

diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 500b96e..a31e27b 100644 (file)
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -20,4 +20,8 @@
 #define ARCH_MAP_VDSO_32               0x2002
 #define ARCH_MAP_VDSO_64               0x2003
 
+#define ARCH_GET_UNTAG_MASK            0x4001
+#define ARCH_ENABLE_TAGGED_ADDR                0x4002
+#define ARCH_GET_MAX_TAG_BITS          0x4003
+
 #endif /* _ASM_X86_PRCTL_H */

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index bbc8c4c..50d9507 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -163,6 +163,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
        savesegment(es, p->thread.es);
        savesegment(ds, p->thread.ds);
+
+       if (p->mm && (clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM)
+               set_bit(MM_CONTEXT_LOCK_LAM, &p->mm->context.flags);
 #else
        p->thread.sp0 = (unsigned long) (childregs + 1);
        savesegment(gs, p->thread.gs);

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index cd34bcf..186f34a 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -743,6 +743,48 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
 }
 #endif
 
+#ifdef CONFIG_ADDRESS_MASKING
+
+#define LAM_U57_BITS 6
+
+static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
+{
+       if (!cpu_feature_enabled(X86_FEATURE_LAM))
+               return -ENODEV;
+
+       /* PTRACE_ARCH_PRCTL */
+       if (current->mm != mm)
+               return -EINVAL;
+
+       if (mmap_write_lock_killable(mm))
+               return -EINTR;
+
+       if (test_bit(MM_CONTEXT_LOCK_LAM, &mm->context.flags)) {
+               mmap_write_unlock(mm);
+               return -EBUSY;
+       }
+
+       if (!nr_bits) {
+               mmap_write_unlock(mm);
+               return -EINVAL;
+       } else if (nr_bits <= LAM_U57_BITS) {
+               mm->context.lam_cr3_mask = X86_CR3_LAM_U57;
+               mm->context.untag_mask =  ~GENMASK(62, 57);
+       } else {
+               mmap_write_unlock(mm);
+               return -EINVAL;
+       }
+
+       write_cr3(__read_cr3() | mm->context.lam_cr3_mask);
+       set_tlbstate_lam_mode(mm);
+       set_bit(MM_CONTEXT_LOCK_LAM, &mm->context.flags);
+
+       mmap_write_unlock(mm);
+
+       return 0;
+}
+#endif
+
 long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
 {
        int ret = 0;
@@ -830,7 +872,18 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
        case ARCH_MAP_VDSO_64:
                return prctl_map_vdso(&vdso_image_64, arg2);
 #endif
-
+#ifdef CONFIG_ADDRESS_MASKING
+       case ARCH_GET_UNTAG_MASK:
+               return put_user(task->mm->context.untag_mask,
+                               (unsigned long __user *)arg2);
+       case ARCH_ENABLE_TAGGED_ADDR:
+               return prctl_enable_tagged_addr(task->mm, arg2);
+       case ARCH_GET_MAX_TAG_BITS:
+               if (!cpu_feature_enabled(X86_FEATURE_LAM))
+                       return put_user(0, (unsigned long __user *)arg2);
+               else
+                       return put_user(LAM_U57_BITS, (unsigned long __user *)arg2);
+#endif
        default:
                ret = -EINVAL;
                break;