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x86/mm: Provide arch_prctl() interface for LAM

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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
This commit is contained in:
Kirill A. Shutemov 2023-03-12 14:26:03 +03:00 committed by Dave Hansen
parent e0bddc19ba
commit 2f8794bd08
4 changed files with 63 additions and 1 deletions
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2
arch/x86/include/asm/mmu.h
View File

@ -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.

4
arch/x86/include/uapi/asm/prctl.h
View File

@ -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 */

3
arch/x86/kernel/process.c
View File

@ -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);

55
arch/x86/kernel/process_64.c
View File

@ -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;