[PATCH v4 06/10] x86/fpu/xstate: Update sanitize_restored_xstate() for supervisor xstates

[Yu-cheng Yu]

The function sanitize_restored_xstate() sanitizes user xstates of an XSAVE
buffer by clearing bits not in the input 'xfeatures' from the buffer's
header->xfeatures, effectively resetting those features back to the init
state.

When supervisor xstates are introduced, it is necessary to make sure only
user xstates are sanitized.  Ensure supervisor bits in header->xfeatures
stay set and supervisor states are not modified.

To make names clear, also:

- Rename the function to sanitize_restored_user_xstate().
- Rename input parameter 'xfeatures' to 'user_xfeatures'.
- In __fpu__restore_sig(), rename 'xfeatures' to 'user_xfeatures'.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
v3:
- Change xfeatures_user to user_xfeatures.

 arch/x86/kernel/fpu/signal.c | 37 +++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index cd6eafba12da..40583487883e 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -211,9 +211,9 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 }
 
 static inline void
-sanitize_restored_xstate(union fpregs_state *state,
-			 struct user_i387_ia32_struct *ia32_env,
-			 u64 xfeatures, int fx_only)
+sanitize_restored_user_xstate(union fpregs_state *state,
+			      struct user_i387_ia32_struct *ia32_env,
+			      u64 user_xfeatures, int fx_only)
 {
 	struct xregs_state *xsave = &state->xsave;
 	struct xstate_header *header = &xsave->header;
@@ -226,13 +226,22 @@ sanitize_restored_xstate(union fpregs_state *state,
 		 */
 
 		/*
-		 * Init the state that is not present in the memory
-		 * layout and not enabled by the OS.
+		 * 'user_xfeatures' might have bits clear which are
+		 * set in header->xfeatures. This represents features that
+		 * were in init state prior to a signal delivery, and need
+		 * to be reset back to the init state.  Clear any user
+		 * feature bits which are set in the kernel buffer to get
+		 * them back to the init state.
+		 *
+		 * Supervisor state is unchanged by input from userspace.
+		 * Ensure supervisor state bits stay set and supervisor
+		 * state is not modified.
 		 */
 		if (fx_only)
 			header->xfeatures = XFEATURE_MASK_FPSSE;
 		else
-			header->xfeatures &= xfeatures;
+			header->xfeatures &= user_xfeatures |
+					     xfeatures_mask_supervisor();
 	}
 
 	if (use_fxsr()) {
@@ -281,7 +290,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 	struct task_struct *tsk = current;
 	struct fpu *fpu = &tsk->thread.fpu;
 	struct user_i387_ia32_struct env;
-	u64 xfeatures = 0;
+	u64 user_xfeatures = 0;
 	int fx_only = 0;
 	int ret = 0;
 
@@ -314,7 +323,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 			trace_x86_fpu_xstate_check_failed(fpu);
 		} else {
 			state_size = fx_sw_user.xstate_size;
-			xfeatures = fx_sw_user.xfeatures;
+			user_xfeatures = fx_sw_user.xfeatures;
 		}
 	}
 
@@ -349,7 +358,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		 */
 		fpregs_lock();
 		pagefault_disable();
-		ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
+		ret = copy_user_to_fpregs_zeroing(buf_fx, user_xfeatures, fx_only);
 		pagefault_enable();
 		if (!ret) {
 			fpregs_mark_activate();
@@ -362,7 +371,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 
 
 	if (use_xsave() && !fx_only) {
-		u64 init_bv = xfeatures_mask_user() & ~xfeatures;
+		u64 init_bv = xfeatures_mask_user() & ~user_xfeatures;
 
 		if (using_compacted_format()) {
 			ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
@@ -375,12 +384,13 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		if (ret)
 			goto err_out;
 
-		sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
+		sanitize_restored_user_xstate(&fpu->state, envp, user_xfeatures,
+					      fx_only);
 
 		fpregs_lock();
 		if (unlikely(init_bv))
 			copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
-		ret = copy_kernel_to_xregs_err(&fpu->state.xsave, xfeatures);
+		ret = copy_kernel_to_xregs_err(&fpu->state.xsave, user_xfeatures);
 
 	} else if (use_fxsr()) {
 		ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
@@ -389,7 +399,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 			goto err_out;
 		}
 
-		sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
+		sanitize_restored_user_xstate(&fpu->state, envp,
+					      user_xfeatures, fx_only);
 
 		fpregs_lock();
 		if (use_xsave()) {
-- 
2.21.0