Commit 2f8794bd authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Dave Hansen
Browse files

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarAlexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/all/20230312112612.31869-9-kirill.shutemov%40linux.intel.com
parent e0bddc19

arch/x86/include/asm/mmu.h

+2 −0
Original line number Diff line number Diff line
@@ -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.

arch/x86/include/uapi/asm/prctl.h

+4 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/process.c

+3 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/process_64.c

+54 −1
Original line number Diff line number Diff line
@@ -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;