powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

Co-developed-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210227011259.11992-10-cmr@codefail.de

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 0575071..e7d612e 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -822,11 +822,11 @@ SYSCALL_DEFINE0(rt_sigreturn)
                 */
                current->thread.regs->msr &= ~MSR_TS_MASK;
                if (!user_read_access_begin(&uc->uc_mcontext, sizeof(uc->uc_mcontext)))
-                       return -EFAULT;
-               if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
-                       user_read_access_end();
                        goto badframe;
-               }
+
+               unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext,
+                                         badframe_block);
+
                user_read_access_end();
        }
 
@@ -836,6 +836,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
        set_thread_flag(TIF_RESTOREALL);
        return 0;
 
+badframe_block:
+       user_read_access_end();
 badframe:
        signal_fault(current, regs, "rt_sigreturn", uc);