powerpc/signal64: Rewrite handle_rt_signal64() 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.

There is no 'unsafe' version of copy_siginfo_to_user, so move it
slightly to allow for a "longer" uaccess block.

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/20210227011259.11992-9-cmr@codefail.de

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 23a44ec3ac01b9f60f3871a786b98b57f48ec599..057507138320fd54bab041256ec7af02b6f8a7f2 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -854,45 +854,53 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
        unsigned long msr = regs->msr;
 
        frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
-       if (!access_ok(frame, sizeof(*frame)))
-               goto badframe;
 
-       err |= __put_user(&frame->info, &frame->pinfo);
-       err |= __put_user(&frame->uc, &frame->puc);
-       err |= copy_siginfo_to_user(&frame->info, &ksig->info);
-       if (err)
+       /*
+        * This only applies when calling unsafe_setup_sigcontext() and must be
+        * called before opening the uaccess window.
+        */
+       if (!MSR_TM_ACTIVE(msr))
+               prepare_setup_sigcontext(tsk);
+
+       if (!user_write_access_begin(frame, sizeof(*frame)))
                goto badframe;
 
+       unsafe_put_user(&frame->info, &frame->pinfo, badframe_block);
+       unsafe_put_user(&frame->uc, &frame->puc, badframe_block);
+
        /* Create the ucontext.  */
-       err |= __put_user(0, &frame->uc.uc_flags);
-       err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
+       unsafe_put_user(0, &frame->uc.uc_flags, badframe_block);
+       unsafe_save_altstack(&frame->uc.uc_stack, regs->gpr[1], badframe_block);
 
        if (MSR_TM_ACTIVE(msr)) {
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
                /* The ucontext_t passed to userland points to the second
                 * ucontext_t (for transactional state) with its uc_link ptr.
                 */
-               err |= __put_user(&frame->uc_transact, &frame->uc.uc_link);
+               unsafe_put_user(&frame->uc_transact, &frame->uc.uc_link, badframe_block);
+
+               user_write_access_end();
+
                err |= setup_tm_sigcontexts(&frame->uc.uc_mcontext,
                                            &frame->uc_transact.uc_mcontext,
                                            tsk, ksig->sig, NULL,
                                            (unsigned long)ksig->ka.sa.sa_handler,
                                            msr);
+
+               if (!user_write_access_begin(&frame->uc.uc_sigmask,
+                                            sizeof(frame->uc.uc_sigmask)))
+                       goto badframe;
+
 #endif
        } else {
-               err |= __put_user(0, &frame->uc.uc_link);
-               prepare_setup_sigcontext(tsk);
-               if (!user_write_access_begin(&frame->uc.uc_mcontext,
-                                            sizeof(frame->uc.uc_mcontext)))
-                       return -EFAULT;
-               err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
-                                               ksig->sig, NULL,
-                                               (unsigned long)ksig->ka.sa.sa_handler, 1);
-               user_write_access_end();
+               unsafe_put_user(0, &frame->uc.uc_link, badframe_block);
+               unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
+                                       NULL, (unsigned long)ksig->ka.sa.sa_handler,
+                                       1, badframe_block);
        }
-       err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
-       if (err)
-               goto badframe;
+
+       unsafe_copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set), badframe_block);
+       user_write_access_end();
 
        /* Make sure signal handler doesn't get spurious FP exceptions */
        tsk->thread.fp_state.fpscr = 0;
@@ -907,6 +915,11 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
                regs->nip = (unsigned long) &frame->tramp[0];
        }
 
+
+       /* Save the siginfo outside of the unsafe block. */
+       if (copy_siginfo_to_user(&frame->info, &ksig->info))
+               goto badframe;
+
        /* Allocate a dummy caller frame for the signal handler. */
        newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
        err |= put_user(regs->gpr[1], (unsigned long __user *)newsp);
@@ -946,6 +959,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 
        return 0;
 
+badframe_block:
+       user_write_access_end();
 badframe:
        signal_fault(current, regs, "handle_rt_signal64", frame);