[PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR

Kirill A. Shutemov
2022-06-10T14:36:22Z

Add a couple 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.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/uapi/asm/prctl.h | 3 +++
arch/x86/kernel/process_64.c | 32 ++++++++++++++++++++++++++++++-
2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 500b96e71f18..38164a05c23c 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -20,4 +20,7 @@
#define ARCH_MAP_VDSO_32 0x2002
#define ARCH_MAP_VDSO_64 0x2003

+#define ARCH_GET_UNTAG_MASK 0x4001
+#define ARCH_ENABLE_TAGGED_ADDR 0x4002
+
#endif /* _ASM_X86_PRCTL_H */
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 1962008fe743..93c8eba1a66d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -742,6 +742,32 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
}
#endif

+static int prctl_enable_tagged_addr(unsigned long nr_bits)
+{
+ struct mm_struct *mm = current->mm;
+
+ /* Already enabled? */
+ if (mm->context.lam_cr3_mask)
+ return -EBUSY;
+
+ /* LAM has to be enabled before spawning threads */
+ if (get_nr_threads(current) > 1)
+ return -EBUSY;
+
+ if (!nr_bits) {
+ return -EINVAL;
+ } else if (nr_bits <= 6) {
+ mm->context.lam_cr3_mask = X86_CR3_LAM_U57;
+ mm->context.untag_mask = ~GENMASK(62, 57);
+ } else {
+ return -EINVAL;
+ }
+
+ /* Update CR3 to get LAM active */
+ switch_mm(current->mm, current->mm, current);
+ return 0;
+}
+
long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
{
int ret = 0;
@@ -829,7 +855,11 @@ 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
-
+ case ARCH_GET_UNTAG_MASK:
+ return put_user(current->mm->context.untag_mask,
+ (unsigned long __user *)arg2);
+ case ARCH_ENABLE_TAGGED_ADDR:
+ return prctl_enable_tagged_addr(arg2);
default:
ret = -EINVAL;
break;
--
2.35.1