ptrace() may request an update to task->fpu that has not yet been
allocated. Detect this case and allocate task->fpu to support the request.
Also, disable the (now unnecessary) associated first-use fault.
No functional change until the kernel supports dynamic user states.
Signed-off-by: Chang S. Bae <chang.seok....@intel.com>
Reviewed-by: Len Brown <len.br...@intel.com>
Cc: x...@kernel.org
Cc: linux-kernel@vger.kernel.org
---
arch/x86/kernel/fpu/regset.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 8d863240b9c6..6b9d0c0a266d 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -125,6 +125,35 @@ int xstateregs_set(struct task_struct *target, const
struct user_regset *regset,
xsave = __xsave(fpu);
+ /*
+ * When a ptracer attempts to write any state in task->fpu but not
allocated,
+ * it dynamically expands the xstate area of fpu->state_ptr.
+ */
+ if (count > get_xstate_size(fpu->state_mask)) {
+ unsigned int offset, size;
+ struct xstate_header hdr;
+ u64 mask;
+
+ offset = offsetof(struct xregs_state, header);
+ size = sizeof(hdr);
+
+ /* Retrieve XSTATE_BV */
+ if (kbuf) {
+ memcpy(&hdr, kbuf + offset, size);
+ } else {
+ ret = __copy_from_user(&hdr, ubuf + offset, size);
+ if (ret)
+ return ret;
+ }
+
+ mask = hdr.xfeatures & xfeatures_mask_user_dynamic;
+ if (!mask) {
+ ret = alloc_xstate_area(fpu, mask, NULL);
+ if (ret)
+ return ret;
+ }
+ }
+
fpu__prepare_write(fpu);
if (using_compacted_format()) {
--
2.17.1
