[PATCH] Make i386 kernel show the unhandled signals

From: Masoud Asgharifard Sharbiani
Date: Sat Jun 09 2007 - 00:06:06 EST

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
different kernels. Like x86_64, it can be disabled by setting
debug.show_unhandled_signals sysctl variable to 0 (or by doing
echo 0 > /proc/sys/debug/show_unhandled_signals)

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;
}


cheers,
Masoud

Signed-off-by: Masoud Sharbiani <masouds@xxxxxxxxxx>

arch/i386/kernel/signal.c | 5 +++++
arch/i386/kernel/traps.c | 7 +++++++
arch/i386/mm/fault.c | 11 +++++++++++
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 +++
include/linux/sysctl.h | 3 +++
kernel/signal.c | 10 ++++++++++
kernel/sysctl.c | 10 ++++++++++
12 files changed, 57 insertions(+), 52 deletions(-)

diff --git a/arch/i386/kernel/signal.c b/arch/i386/kernel/signal.c
index d574e38..828dcb0 100644
--- a/arch/i386/kernel/signal.c
+++ b/arch/i386/kernel/signal.c
@@ -199,6 +199,11 @@ asmlinkage int sys_sigreturn(unsigned long __unused)
return eax;

badframe:
+ if (show_unhandled_signals && printk_ratelimit())
+ printk("%s[%d] bad frame in sigreturn frame:%p eip:%lx esp:%lx oeax:%lx\n",
+ 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 90da057..bccc5b4 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -610,6 +610,13 @@ 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 29d7d61..2aa4206 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
@@ -465,6 +467,15 @@ 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/i386/mm/init.c b/arch/i386/mm/init.c
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 cb29fb9..4f46b4d 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -577,7 +577,8 @@ 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,
@@ -681,7 +682,8 @@ 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 bfb62a1..73917cf 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,
@@ -489,7 +479,8 @@ 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 1ad5111..19a6f5b 100644
--- a/arch/x86_64/mm/init.c
+++ b/arch/x86_64/mm/init.c
@@ -690,41 +690,6 @@ 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 9a5eac5..aa2c243 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -238,12 +238,15 @@ 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/include/linux/sysctl.h b/include/linux/sysctl.h
index 47f1c53..a4fd7f1 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -835,6 +835,9 @@ enum {
};

/* CTL_DEBUG names: */
+enum {
+ DEBUG_UNHANDLED_SIGNALS = 1,
+};

/* CTL_DEV names: */
enum {
diff --git a/kernel/signal.c b/kernel/signal.c
index fe590e0..ce6085f 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 30ee462..9486870 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1026,6 +1026,16 @@ static ctl_table fs_table[] = {
};

static ctl_table debug_table[] = {
+#ifdef CONFIG_X86
+ {
+ .ctl_name = DEBUG_UNHANDLED_SIGNALS,
+ .procname = "show-unhandled-signals",
+ .data = &show_unhandled_signals,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
+#endif
{ .ctl_name = 0 }
};

-
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