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ARC: Signal handling

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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>
This commit is contained in:
Vineet Gupta 2013-01-18 15:12:19 +05:30
parent d8005e6b95
commit c3581039b6
6 changed files with 449 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/arc/Kconfig
View File

@ -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

35
arch/arc/include/asm/entry.h
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@ -165,6 +165,41 @@
.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
*-------------------------------------------------------------*/

22
arch/arc/include/asm/sigcontext.h Normal file
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@ -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 */

27
arch/arc/include/asm/signal.h Normal file
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@ -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 */

11
arch/arc/kernel/entry.S
View File

@ -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

356
arch/arc/kernel/signal.c Normal file
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@ -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);
}