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    SubjectRe: i386-show-unhandled-signals-v3
    On 7/25/07, Kirill Korotaev <dev@openvz.org> wrote:
    > plz don't enable it by default... :/
    > any user can spam syslog with these messages and if syslog is run as root
    > can take the whole diskspace...


    Yeah, but:
    1) Right now (without this patch), it is enabled by default with _no_
    rate control in _all_ kernels; I ran the tiny program that is here,
    and it wasn't fun to watch.
    2) With this patch it will be rate controlled using
    printk_ratelimit(), thus reducing the amount of spam immensely.

    Of course, we can disable both of them, is this what you (and
    everybody else) want?

    Masoud

    > Thanks,
    > Kirill
    >
    > Masoud Asgharifard Sharbiani wrote:
    > > Hello,
    > > This patch makes the i386 behave the same way that x86_64 does when a
    > > segfault happens. A line gets printed to the kernel log so that tools
    > > that
    > > need to check for failures can behave more uniformly between
    > > debug.show_unhandled_signals sysctl variable to 0 (or by doing echo 0 >
    > > /proc/sys/debug/exception-trace)
    > >
    > > Also, all of the lines being printed are now using printk_ratelimit() to
    > > deny the ability of DoS from a local user with a program like the
    > > following:
    > >
    > > main()
    > > {
    > > while (1)
    > > if (!fork()) *(int *)0 = 0;
    > > }
    > >
    > > This new revision also includes the fix that Andrew did which got rid of
    > > new sysctl that was added to the system in earlier versions of this.
    > > Also, 'show-unhandled-signals' sysctl has been renamed back to the old
    > > 'exception-trace' to avoid breakage of people's scripts.
    > >
    > > cheers,
    > > Masoud Sharbiani
    > >
    > > Signed-off-by: Masoud Sharbiani <masouds@google.com>
    > > Cc: Andi Kleen <ak@suse.de>
    > >
    > > ---
    > > arch/i386/kernel/signal.c | 7 +++++++
    > > arch/i386/kernel/traps.c | 7 +++++++
    > > arch/i386/mm/fault.c | 10 ++++++++++
    > > arch/x86_64/kernel/signal.c | 2 +-
    > > arch/x86_64/kernel/traps.c | 6 ++++--
    > > arch/x86_64/mm/fault.c | 15 +++------------
    > > arch/x86_64/mm/init.c | 35 -----------------------------------
    > > include/asm-x86_64/proto.h | 2 --
    > > include/linux/signal.h | 3 +++
    > > kernel/signal.c | 10 ++++++++++
    > > kernel/sysctl.c | 10 ++++++++++
    > > 11 files changed, 55 insertions(+), 52 deletions(-)
    > >
    > > diff --git a/arch/i386/kernel/signal.c b/arch/i386/kernel/signal.c
    > > index d574e38..f5dd856 100644
    > > --- a/arch/i386/kernel/signal.c
    > > +++ b/arch/i386/kernel/signal.c
    > > @@ -199,6 +199,13 @@ asmlinkage int sys_sigreturn(unsigned long __unused)
    > > return eax;
    > >
    > > badframe:
    > > + if (show_unhandled_signals && printk_ratelimit())
    > > + printk("%s%s[%d] bad frame in sigreturn frame:%p eip:%lx"
    > > + " esp:%lx oeax:%lx\n",
    > > + current->pid > 1 ? KERN_INFO : KERN_EMERG,
    > > + current->comm, current->pid, frame, regs->eip,
    > > + regs->esp, regs->orig_eax);
    > > +
    > > force_sig(SIGSEGV, current);
    > > return 0;
    > > }
    > > diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
    > > index 18c1c28..c20283c 100644
    > > --- a/arch/i386/kernel/traps.c
    > > +++ b/arch/i386/kernel/traps.c
    > > @@ -611,6 +611,13 @@ fastcall void __kprobes do_general_protection(struct pt_regs * regs,
    > >
    > > current->thread.error_code = error_code;
    > > current->thread.trap_no = 13;
    > > + if (show_unhandled_signals && unhandled_signal(current, SIGSEGV) &&
    > > + printk_ratelimit())
    > > + printk(KERN_INFO
    > > + "%s[%d] general protection eip:%lx esp:%lx error:%lx\n",
    > > + current->comm, current->pid,
    > > + regs->eip, regs->esp, error_code);
    > > +
    > > force_sig(SIGSEGV, current);
    > > return;
    > >
    > > diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
    > > index 1ecb3e4..52c940b 100644
    > > --- a/arch/i386/mm/fault.c
    > > +++ b/arch/i386/mm/fault.c
    > > @@ -283,6 +283,8 @@ static inline int vmalloc_fault(unsigned long address)
    > > return 0;
    > > }
    > >
    > > +int show_unhandled_signals = 1;
    > > +
    > > /*
    > > * This routine handles page faults. It determines the address,
    > > * and the problem, and then passes it off to one of the appropriate
    > > @@ -470,6 +472,14 @@ bad_area_nosemaphore:
    > > if (is_prefetch(regs, address, error_code))
    > > return;
    > >
    > > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
    > > + printk_ratelimit()) {
    > > + printk("%s%s[%d]: segfault at %08lx eip %08lx "
    > > + "esp %08lx error %lx\n",
    > > + tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
    > > + tsk->comm, tsk->pid, address, regs->eip,
    > > + regs->esp, error_code);
    > > + }
    > > tsk->thread.cr2 = address;
    > > /* Kernel addresses are always protection faults */
    > > tsk->thread.error_code = error_code | (address >= TASK_SIZE);
    > > diff --git a/arch/x86_64/kernel/signal.c b/arch/x86_64/kernel/signal.c
    > > index 290f5d8..f9506f6 100644
    > > --- a/arch/x86_64/kernel/signal.c
    > > +++ b/arch/x86_64/kernel/signal.c
    > > @@ -480,7 +480,7 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
    > > void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
    > > {
    > > struct task_struct *me = current;
    > > - if (exception_trace)
    > > + if (show_unhandled_signals && printk_ratelimit())
    > > printk("%s[%d] bad frame in %s frame:%p rip:%lx rsp:%lx orax:%lx\n",
    > > me->comm,me->pid,where,frame,regs->rip,regs->rsp,regs->orig_rax);
    > >
    > > diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
    > > index 74cbeb2..b9660c4 100644
    > > --- a/arch/x86_64/kernel/traps.c
    > > +++ b/arch/x86_64/kernel/traps.c
    > > @@ -580,7 +580,8 @@ static void __kprobes do_trap(int trapnr, int signr, char *str,
    > > tsk->thread.error_code = error_code;
    > > tsk->thread.trap_no = trapnr;
    > >
    > > - if (exception_trace && unhandled_signal(tsk, signr))
    > > + if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
    > > + printk_ratelimit())
    > > printk(KERN_INFO
    > > "%s[%d] trap %s rip:%lx rsp:%lx error:%lx\n",
    > > tsk->comm, tsk->pid, str,
    > > @@ -684,7 +685,8 @@ asmlinkage void __kprobes do_general_protection(struct pt_regs * regs,
    > > tsk->thread.error_code = error_code;
    > > tsk->thread.trap_no = 13;
    > >
    > > - if (exception_trace && unhandled_signal(tsk, SIGSEGV))
    > > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
    > > + printk_ratelimit())
    > > printk(KERN_INFO
    > > "%s[%d] general protection rip:%lx rsp:%lx error:%lx\n",
    > > tsk->comm, tsk->pid,
    > > diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
    > > index 635e58d..0412824 100644
    > > --- a/arch/x86_64/mm/fault.c
    > > +++ b/arch/x86_64/mm/fault.c
    > > @@ -221,16 +221,6 @@ static int is_errata93(struct pt_regs *regs, unsigned long address)
    > > return 0;
    > > }
    > >
    > > -int unhandled_signal(struct task_struct *tsk, int sig)
    > > -{
    > > - if (is_init(tsk))
    > > - return 1;
    > > - if (tsk->ptrace & PT_PTRACED)
    > > - return 0;
    > > - return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
    > > - (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
    > > -}
    > > -
    > > static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
    > > unsigned long error_code)
    > > {
    > > @@ -302,7 +292,7 @@ static int vmalloc_fault(unsigned long address)
    > > }
    > >
    > > int page_fault_trace = 0;
    > > -int exception_trace = 1;
    > > +int show_unhandled_signals = 1;
    > >
    > > /*
    > > * This routine handles page faults. It determines the address,
    > > @@ -495,7 +485,8 @@ bad_area_nosemaphore:
    > > (address >> 32))
    > > return;
    > >
    > > - if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
    > > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
    > > + printk_ratelimit()) {
    > > printk(
    > > "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
    > > tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
    > > diff --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
    > > index 9a0e98a..5096168 100644
    > > --- a/arch/x86_64/mm/init.c
    > > +++ b/arch/x86_64/mm/init.c
    > > @@ -697,41 +697,6 @@ int kern_addr_valid(unsigned long addr)
    > > return pfn_valid(pte_pfn(*pte));
    > > }
    > >
    > > -#ifdef CONFIG_SYSCTL
    > > -#include <linux/sysctl.h>
    > > -
    > > -extern int exception_trace, page_fault_trace;
    > > -
    > > -static ctl_table debug_table2[] = {
    > > - {
    > > - .ctl_name = 99,
    > > - .procname = "exception-trace",
    > > - .data = &exception_trace,
    > > - .maxlen = sizeof(int),
    > > - .mode = 0644,
    > > - .proc_handler = proc_dointvec
    > > - },
    > > - {}
    > > -};
    > > -
    > > -static ctl_table debug_root_table2[] = {
    > > - {
    > > - .ctl_name = CTL_DEBUG,
    > > - .procname = "debug",
    > > - .mode = 0555,
    > > - .child = debug_table2
    > > - },
    > > - {}
    > > -};
    > > -
    > > -static __init int x8664_sysctl_init(void)
    > > -{
    > > - register_sysctl_table(debug_root_table2);
    > > - return 0;
    > > -}
    > > -__initcall(x8664_sysctl_init);
    > > -#endif
    > > -
    > > /* A pseudo VMA to allow ptrace access for the vsyscall page. This only
    > > covers the 64bit vsyscall page now. 32bit has a real VMA now and does
    > > not need special handling anymore. */
    > > diff --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
    > > index 85255db..4fad501 100644
    > > --- a/include/asm-x86_64/proto.h
    > > +++ b/include/asm-x86_64/proto.h
    > > @@ -75,8 +75,6 @@ extern void setup_node_bootmem(int nodeid, unsigned long start, unsigned long en
    > > extern void early_quirks(void);
    > > extern void check_efer(void);
    > >
    > > -extern int unhandled_signal(struct task_struct *tsk, int sig);
    > > -
    > > extern void select_idle_routine(const struct cpuinfo_x86 *c);
    > >
    > > extern unsigned long table_start, table_end;
    > > diff --git a/include/linux/signal.h b/include/linux/signal.h
    > > index ea91abe..0ae3388 100644
    > > --- a/include/linux/signal.h
    > > +++ b/include/linux/signal.h
    > > @@ -237,12 +237,15 @@ extern int group_send_sig_info(int sig, struct siginfo *info, struct task_struct
    > > extern int __group_send_sig_info(int, struct siginfo *, struct task_struct *);
    > > extern long do_sigpending(void __user *, unsigned long);
    > > extern int sigprocmask(int, sigset_t *, sigset_t *);
    > > +extern int show_unhandled_signals;
    > >
    > > struct pt_regs;
    > > extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
    > >
    > > extern struct kmem_cache *sighand_cachep;
    > >
    > > +int unhandled_signal(struct task_struct *tsk, int sig);
    > > +
    > > /*
    > > * In POSIX a signal is sent either to a specific thread (Linux task)
    > > * or to the process as a whole (Linux thread group). How the signal
    > > diff --git a/kernel/signal.c b/kernel/signal.c
    > > index 39d1227..ef8156a 100644
    > > --- a/kernel/signal.c
    > > +++ b/kernel/signal.c
    > > @@ -255,6 +255,16 @@ flush_signal_handlers(struct task_struct *t, int force_default)
    > > }
    > > }
    > >
    > > +int unhandled_signal(struct task_struct *tsk, int sig)
    > > +{
    > > + if (is_init(tsk))
    > > + return 1;
    > > + if (tsk->ptrace & PT_PTRACED)
    > > + return 0;
    > > + return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
    > > + (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
    > > +}
    > > +
    > >
    > > /* Notify the system that a driver wants to block all signals for this
    > > * process, and wants to be notified if any signals at all were to be
    > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
    > > index 7063ebc..af7002f 100644
    > > --- a/kernel/sysctl.c
    > > +++ b/kernel/sysctl.c
    > > @@ -1153,6 +1153,16 @@ static ctl_table fs_table[] = {
    > > };
    > >
    > > static ctl_table debug_table[] = {
    > > +#ifdef CONFIG_X86
    > > + {
    > > + .ctl_name = CTL_UNNUMBERED,
    > > + .procname = "exception-trace",
    > > + .data = &show_unhandled_signals,
    > > + .maxlen = sizeof(int),
    > > + .mode = 0644,
    > > + .proc_handler = proc_dointvec
    > > + },
    > > +#endif
    > > { .ctl_name = 0 }
    > > };
    > >
    > > -
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    >
    >
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