x86/fpu: Get rid of copy_supervisor_to_kernel()

If the fast path of restoring the FPU state on sigreturn fails or is not
taken and the current task's FPU is active then the FPU has to be
deactivated for the slow path to allow a safe update of the tasks FPU
memory state.

With supervisor states enabled, this requires to save the supervisor state
in the memory state first. Supervisor states require XSAVES so saving only
the supervisor state requires to reshuffle the memory buffer because XSAVES
uses the compacted format and therefore stores the supervisor states at the
beginning of the memory state. That's just an overengineered optimization.

Get rid of it and save the full state for this case.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121453.734561971@linutronix.de

1 files changed, 0 insertions, 55 deletions

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 579e343e6654..427977b52c6c 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1204,61 +1204,6 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
 	return 0;
 }
 
-/*
- * Save only supervisor states to the kernel buffer.  This blows away all
- * old states, and is intended to be used only in __fpu__restore_sig(), where
- * user states are restored from the user buffer.
- */
-void copy_supervisor_to_kernel(struct xregs_state *xstate)
-{
-	struct xstate_header *header;
-	u64 max_bit, min_bit;
-	u32 lmask, hmask;
-	int err, i;
-
-	if (WARN_ON(!boot_cpu_has(X86_FEATURE_XSAVES)))
-		return;
-
-	if (!xfeatures_mask_supervisor())
-		return;
-
-	max_bit = __fls(xfeatures_mask_supervisor());
-	min_bit = __ffs(xfeatures_mask_supervisor());
-
-	lmask = xfeatures_mask_supervisor();
-	hmask = xfeatures_mask_supervisor() >> 32;
-	XSTATE_OP(XSAVES, xstate, lmask, hmask, err);
-
-	/* We should never fault when copying to a kernel buffer: */
-	if (WARN_ON_FPU(err))
-		return;
-
-	/*
-	 * At this point, the buffer has only supervisor states and must be
-	 * converted back to normal kernel format.
-	 */
-	header = &xstate->header;
-	header->xcomp_bv |= xfeatures_mask_all;
-
-	/*
-	 * This only moves states up in the buffer.  Start with
-	 * the last state and move backwards so that states are
-	 * not overwritten until after they are moved.  Note:
-	 * memmove() allows overlapping src/dst buffers.
-	 */
-	for (i = max_bit; i >= min_bit; i--) {
-		u8 *xbuf = (u8 *)xstate;
-
-		if (!((header->xfeatures >> i) & 1))
-			continue;
-
-		/* Move xfeature 'i' into its normal location */
-		memmove(xbuf + xstate_comp_offsets[i],
-			xbuf + xstate_supervisor_only_offsets[i],
-			xstate_sizes[i]);
-	}
-}
-
 /**
  * copy_dynamic_supervisor_to_kernel() - Save dynamic supervisor states to
  *                                       an xsave area