ARC: Signal handling

Includes following fixes courtesy review by Al-Viro

* Tracer poke to Callee-regs were lost

  Before going off into do_signal( ) we save the user-mode callee regs
  (as they are not saved by default as part of pt_regs). This is to make
  sure that that a Tracer (if tracing related signal) is able to do likes
  of PEEKUSR(callee-reg).

  However in return path we were simply discarding the user-mode callee
  regs, which would break a POKEUSR(callee-reg) from a tracer.

* Issue related to multiple syscall restarts are addressed in next patch

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Acked-by: Jonas Bonn <jonas@southpole.se>

6 files changed, 449 insertions, 3 deletions

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index a4e9806ace23..756beffd20cb 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -20,6 +20,7 @@ config ARC
         select GENERIC_KERNEL_EXECVE
         select GENERIC_KERNEL_THREAD
         select GENERIC_PENDING_IRQ if SMP
+        select GENERIC_SIGALTSTACK
         select GENERIC_SMP_IDLE_THREAD
         select HAVE_GENERIC_HARDIRQS
         select MODULES_USE_ELF_RELA
diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 63705b12d911..6b42bf5c45ec 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -166,6 +166,41 @@
 .endm
 
 /*--------------------------------------------------------------
+ * RESTORE_CALLEE_SAVED_USER:
+ * This is called after do_signal where tracer might have changed callee regs
+ * thus we need to restore the reg file.
+ * Special case handling is required for r25 in case it is used by kernel
+ *  for caching task ptr. Ptrace would have modified on-kernel-stack value of
+ *  r25, which needs to be shoved back into task->thread.user_r25 where from
+ *  Low level exception/ISR return code will retrieve to populate with rest of
+ *  callee reg-file.
+ *-------------------------------------------------------------*/
+.macro RESTORE_CALLEE_SAVED_USER
+
+        add     sp, sp, 4   /* skip "callee_regs->stack_place_holder" */
+
+#ifdef CONFIG_ARC_CURR_IN_REG
+        ld.ab   r12, [sp, 4]
+        st      r12, [r25, TASK_THREAD + THREAD_USER_R25]
+#else
+        ld.ab   r25, [sp, 4]
+#endif
+
+        ld.ab   r24, [sp, 4]
+        ld.ab   r23, [sp, 4]
+        ld.ab   r22, [sp, 4]
+        ld.ab   r21, [sp, 4]
+        ld.ab   r20, [sp, 4]
+        ld.ab   r19, [sp, 4]
+        ld.ab   r18, [sp, 4]
+        ld.ab   r17, [sp, 4]
+        ld.ab   r16, [sp, 4]
+        ld.ab   r15, [sp, 4]
+        ld.ab   r14, [sp, 4]
+        ld.ab   r13, [sp, 4]
+.endm
+
+/*--------------------------------------------------------------
  * Super FAST Restore callee saved regs by simply re-adjusting SP
  *-------------------------------------------------------------*/
 .macro DISCARD_CALLEE_SAVED_USER
diff --git a/arch/arc/include/asm/sigcontext.h b/arch/arc/include/asm/sigcontext.h
new file mode 100644
index 000000000000..9678a11fc158
--- /dev/null
+++ b/arch/arc/include/asm/sigcontext.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _ASM_ARC_SIGCONTEXT_H
+#define _ASM_ARC_SIGCONTEXT_H
+
+#include <asm/ptrace.h>
+
+/*
+ * Signal context structure - contains all info to do with the state
+ * before the signal handler was invoked.
+ */
+struct sigcontext {
+        struct user_regs_struct regs;
+};
+
+#endif /* _ASM_ARC_SIGCONTEXT_H */
diff --git a/arch/arc/include/asm/signal.h b/arch/arc/include/asm/signal.h
new file mode 100644
index 000000000000..fad62f7f42d6
--- /dev/null
+++ b/arch/arc/include/asm/signal.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Amit Bhor, Sameer Dhavale: Codito Technologies 2004
+ */
+
+#ifndef _ASM_ARC_SIGNAL_H
+#define _ASM_ARC_SIGNAL_H
+
+/*
+ * This is much needed for ARC sigreturn optimization.
+ * This allows uClibc to piggback the addr of a sigreturn stub in sigaction,
+ * which allows sigreturn based re-entry into kernel after handling signal.
+ * W/o this kernel needs to "synthesize" the sigreturn trampoline on user
+ * mode stack which in turn forces the following:
+ * -TLB Flush (after making the stack page executable)
+ * -Cache line Flush (to make I/D Cache lines coherent)
+ */
+#define SA_RESTORER     0x04000000
+
+#include <asm-generic/signal.h>
+
+#endif /* _ASM_ARC_SIGNAL_H */
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index ed08ac14fbc4..d625b77c14bd 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -470,7 +470,11 @@ resume_user_mode_begin:
 
         bbit0  r9, TIF_SIGPENDING, .Lchk_notify_resume
 
-        ; save CALLEE Regs.
+        ; Normal Trap/IRQ entry only saves Scratch (caller-saved) regs
+        ; in pt_reg since the "C" ABI (kernel code) will automatically
+        ; save/restore callee-saved regs.
+        ;
+        ; However, here we need to explicitly save callee regs because
         ; (i)  If this signal causes coredump - full regfile needed
         ; (ii) If signal is SIGTRAP/SIGSTOP, task is being traced thus
         ;      tracer might call PEEKUSR(CALLEE reg)
@@ -484,8 +488,9 @@ resume_user_mode_begin:
 
         bl  @do_signal
 
-        ; unwind SP for cheap discard of Callee saved Regs
-        DISCARD_CALLEE_SAVED_USER
+        ; Ideally we want to discard the Callee reg above, however if this was
+        ; a tracing signal, tracer could have done a POKEUSR(CALLEE reg)
+        RESTORE_CALLEE_SAVED_USER
 
         b      resume_user_mode_begin   ; loop back to start of U mode ret
 
diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
new file mode 100644
index 000000000000..ab8ed5a55461
--- /dev/null
+++ b/arch/arc/kernel/signal.c
@@ -0,0 +1,356 @@
+/*
+ * Signal Handling for ARC
+ *
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * vineetg: Jan 2010 (Restarting of timer related syscalls)
+ *
+ * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
+ *  -do_signal() supports TIF_RESTORE_SIGMASK
+ *  -do_signal() no loner needs oldset, required by OLD sys_sigsuspend
+ *  -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen
+ *  -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed
+ *  -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves
+ *   the job to do_signal()
+ *
+ * vineetg: July 2009
+ *  -Modified Code to support the uClibc provided userland sigreturn stub
+ *   to avoid kernel synthesing it on user stack at runtime, costing TLB
+ *   probes and Cache line flushes.
+ *
+ * vineetg: July 2009
+ *  -In stash_usr_regs( ) and restore_usr_regs( ), save/restore of user regs
+ *   in done in block copy rather than one word at a time.
+ *   This saves around 2K of code and improves LMBench lat_sig <catch>
+ *
+ * rajeshwarr: Feb 2009
+ *  - Support for Realtime Signals
+ *
+ * vineetg: Aug 11th 2008: Bug #94183
+ *  -ViXS were still seeing crashes when using insmod to load drivers.
+ *   It turned out that the code to change Execute permssions for TLB entries
+ *   of user was not guarded for interrupts (mod_tlb_permission)
+ *   This was cauing TLB entries to be overwritten on unrelated indexes
+ *
+ * Vineetg: July 15th 2008: Bug #94183
+ *  -Exception happens in Delay slot of a JMP, and before user space resumes,
+ *   Signal is delivered (Ctrl + C) = >SIGINT.
+ *   setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler
+ *   to run, but doesn't clear the Delay slot bit from status32. As a result,
+ *   on resuming user mode, signal handler branches off to BTA of orig JMP
+ *  -FIX: clear the DE bit from status32 in setup_frame( )
+ *
+ * Rahul Trivedi, Kanika Nema: Codito Technologies 2004
+ */
+
+#include <linux/signal.h>
+#include <linux/ptrace.h>
+#include <linux/personality.h>
+#include <linux/uaccess.h>
+#include <linux/syscalls.h>
+#include <linux/tracehook.h>
+#include <asm/ucontext.h>
+
+struct rt_sigframe {
+        struct siginfo info;
+        struct ucontext uc;
+#define MAGIC_SIGALTSTK         0x07302004
+        unsigned int sigret_magic;
+};
+
+static int
+stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
+               sigset_t *set)
+{
+        int err;
+        err = __copy_to_user(&(sf->uc.uc_mcontext.regs), regs,
+                             sizeof(sf->uc.uc_mcontext.regs.scratch));
+        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
+
+        return err;
+}
+
+static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
+{
+        sigset_t set;
+        int err;
+
+        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
+        if (!err)
+                set_current_blocked(&set);
+
+        err |= __copy_from_user(regs, &(sf->uc.uc_mcontext.regs),
+                                sizeof(sf->uc.uc_mcontext.regs.scratch));
+
+        return err;
+}
+
+static inline int is_do_ss_needed(unsigned int magic)
+{
+        if (MAGIC_SIGALTSTK == magic)
+                return 1;
+        else
+                return 0;
+}
+
+SYSCALL_DEFINE0(rt_sigreturn)
+{
+        struct rt_sigframe __user *sf;
+        unsigned int magic;
+        int err;
+        struct pt_regs *regs = current_pt_regs();
+
+        /* Always make any pending restarted system calls return -EINTR */
+        current_thread_info()->restart_block.fn = do_no_restart_syscall;
+
+        /* Since we stacked the signal on a word boundary,
+         * then 'sp' should be word aligned here.  If it's
+         * not, then the user is trying to mess with us.
+         */
+        if (regs->sp & 3)
+                goto badframe;
+
+        sf = (struct rt_sigframe __force __user *)(regs->sp);
+
+        if (!access_ok(VERIFY_READ, sf, sizeof(*sf)))
+                goto badframe;
+
+        err = restore_usr_regs(regs, sf);
+        err |= __get_user(magic, &sf->sigret_magic);
+        if (err)
+                goto badframe;
+
+        if (unlikely(is_do_ss_needed(magic)))
+                if (restore_altstack(&sf->uc.uc_stack))
+                        goto badframe;
+
+        return regs->r0;
+
+badframe:
+        force_sig(SIGSEGV, current);
+        return 0;
+}
+
+/*
+ * Determine which stack to use..
+ */
+static inline void __user *get_sigframe(struct k_sigaction *ka,
+                                        struct pt_regs *regs,
+                                        unsigned long framesize)
+{
+        unsigned long sp = regs->sp;
+        void __user *frame;
+
+        /* This is the X/Open sanctioned signal stack switching */
+        if ((ka->sa.sa_flags & SA_ONSTACK) && !sas_ss_flags(sp))
+                sp = current->sas_ss_sp + current->sas_ss_size;
+
+        /* No matter what happens, 'sp' must be word
+         * aligned otherwise nasty things could happen
+         */
+
+        /* ATPCS B01 mandates 8-byte alignment */
+        frame = (void __user *)((sp - framesize) & ~7);
+
+        /* Check that we can actually write to the signal frame */
+        if (!access_ok(VERIFY_WRITE, frame, framesize))
+                frame = NULL;
+
+        return frame;
+}
+
+/*
+ * translate the signal
+ */
+static inline int map_sig(int sig)
+{
+        struct thread_info *thread = current_thread_info();
+        if (thread->exec_domain && thread->exec_domain->signal_invmap
+            && sig < 32)
+                sig = thread->exec_domain->signal_invmap[sig];
+        return sig;
+}
+
+static int
+setup_rt_frame(int signo, struct k_sigaction *ka, siginfo_t *info,
+               sigset_t *set, struct pt_regs *regs)
+{
+        struct rt_sigframe __user *sf;
+        unsigned int magic = 0;
+        int err = 0;
+
+        sf = get_sigframe(ka, regs, sizeof(struct rt_sigframe));
+        if (!sf)
+                return 1;
+
+        /*
+         * SA_SIGINFO requires 3 args to signal handler:
+         *  #1: sig-no (common to any handler)
+         *  #2: struct siginfo
+         *  #3: struct ucontext (completely populated)
+         */
+        if (unlikely(ka->sa.sa_flags & SA_SIGINFO)) {
+                err |= copy_siginfo_to_user(&sf->info, info);
+                err |= __put_user(0, &sf->uc.uc_flags);
+                err |= __put_user(NULL, &sf->uc.uc_link);
+                err |= __save_altstack(&sf->uc.uc_stack, regs->sp);
+
+                /* setup args 2 and 3 for user mode handler */
+                regs->r1 = (unsigned long)&sf->info;
+                regs->r2 = (unsigned long)&sf->uc;
+
+                /*
+                 * small optim to avoid unconditonally calling do_sigaltstack
+                 * in sigreturn path, now that we only have rt_sigreturn
+                 */
+                magic = MAGIC_SIGALTSTK;
+        }
+
+        /*
+         * w/o SA_SIGINFO, struct ucontext is partially populated (only
+         * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
+         * during signal handler execution. This works for SA_SIGINFO as well
+         * although the semantics are now overloaded (the same reg state can be
+         * inspected by userland: but are they allowed to fiddle with it ?
+         */
+        err |= stash_usr_regs(sf, regs, set);
+        err |= __put_user(magic, &sf->sigret_magic);
+        if (err)
+                return err;
+
+        /* #1 arg to the user Signal handler */
+        regs->r0 = map_sig(signo);
+
+        /* setup PC of user space signal handler */
+        regs->ret = (unsigned long)ka->sa.sa_handler;
+
+        /*
+         * handler returns using sigreturn stub provided already by userpsace
+         */
+        BUG_ON(!(ka->sa.sa_flags & SA_RESTORER));
+        regs->blink = (unsigned long)ka->sa.sa_restorer;
+
+        /* User Stack for signal handler will be above the frame just carved */
+        regs->sp = (unsigned long)sf;
+
+        /*
+         * Bug 94183, Clear the DE bit, so that when signal handler
+         * starts to run, it doesn't use BTA
+         */
+        regs->status32 &= ~STATUS_DE_MASK;
+        regs->status32 |= STATUS_L_MASK;
+
+        return err;
+}
+
+static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
+{
+        switch (regs->r0) {
+        case -ERESTART_RESTARTBLOCK:
+        case -ERESTARTNOHAND:
+                /*
+                 * ERESTARTNOHAND means that the syscall should
+                 * only be restarted if there was no handler for
+                 * the signal, and since we only get here if there
+                 * is a handler, we don't restart
+                 */
+                regs->r0 = -EINTR;   /* ERESTART_xxx is internal */
+                break;
+
+        case -ERESTARTSYS:
+                /*
+                 * ERESTARTSYS means to restart the syscall if
+                 * there is no handler or the handler was
+                 * registered with SA_RESTART
+                 */
+                if (!(ka->sa.sa_flags & SA_RESTART)) {
+                        regs->r0 = -EINTR;
+                        break;
+                }
+                /* fallthrough */
+
+        case -ERESTARTNOINTR:
+                /*
+                 * ERESTARTNOINTR means that the syscall should
+                 * be called again after the signal handler returns.
+                 * Setup reg state just as it was before doing the trap
+                 * r0 has been clobbered with sys call ret code thus it
+                 * needs to be reloaded with orig first arg to syscall
+                 * in orig_r0. Rest of relevant reg-file:
+                 * r8 (syscall num) and (r1 - r7) will be reset to
+                 * their orig user space value when we ret from kernel
+                 */
+                regs->r0 = regs->orig_r0;
+                regs->ret -= 4;
+                break;
+        }
+}
+
+/*
+ * OK, we're invoking a handler
+ */
+static void
+handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
+              struct pt_regs *regs)
+{
+        sigset_t *oldset = sigmask_to_save();
+        int ret;
+
+        /* Set up the stack frame */
+        ret = setup_rt_frame(sig, ka, info, oldset, regs);
+
+        if (ret)
+                force_sigsegv(sig, current);
+        else
+                signal_delivered(sig, info, ka, regs, 0);
+}
+
+void do_signal(struct pt_regs *regs)
+{
+        struct k_sigaction ka;
+        siginfo_t info;
+        int signr;
+        int restart_scall;
+
+        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+
+        /* Are we from a system call? */
+        restart_scall = in_syscall(regs);
+
+        if (signr > 0) {
+                if (restart_scall)
+                        arc_restart_syscall(&ka, regs);
+
+                handle_signal(signr, &ka, &info, regs);
+                return;
+        }
+
+        if (restart_scall) {
+                /* No handler for syscall: restart it */
+                if (regs->r0 == -ERESTARTNOHAND ||
+                    regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
+                        regs->r0 = regs->orig_r0;
+                        regs->ret -= 4;
+                } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
+                        regs->r8 = __NR_restart_syscall;
+                        regs->ret -= 4;
+                }
+        }
+
+        /* If there's no signal to deliver, restore the saved sigmask back */
+        restore_saved_sigmask();
+}
+
+void do_notify_resume(struct pt_regs *regs)
+{
+        /*
+         * ASM glue gaurantees that this is only called when returning to
+         * user mode
+         */
+        if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME))
+                tracehook_notify_resume(regs);
+}