[PATCH] x86: Fix i386 and x86_64 fault information pollution

a userspace fault or a kernelspace fault which will result in the
immediate death of the process.  They should not be filled in as a
result of a kernelspace fault which can be fixed up.

Otherwise, if the process is handling SIGSEGV and examining the fault
information, this can result in the kernel space fault trashing the
previously stored fault information if it arrives between the
userspace fault happening and the SIGSEGV being delivered to the process.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Jan Beulich <jbeulich@novell.com>
--
 arch/i386/kernel/traps.c   |   24 ++++++++++++++++++------
 arch/x86_64/kernel/traps.c |   30 +++++++++++++++++++++++-------
 2 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index af0d3f70a8174d6b0a3b284dd46495e64c4deb34..58dfecc8e36c8150f51623469f947ce5b3670bd1 100644 (file)
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -476,8 +476,6 @@ static void __kprobes do_trap(int trapnr, int signr, char *str, int vm86,
                              siginfo_t *info)
 {
        struct task_struct *tsk = current;
-       tsk->thread.error_code = error_code;
-       tsk->thread.trap_no = trapnr;
 
        if (regs->eflags & VM_MASK) {
                if (vm86)
@@ -489,6 +487,18 @@ static void __kprobes do_trap(int trapnr, int signr, char *str, int vm86,
                goto kernel_trap;
 
        trap_signal: {
+               /*
+                * We want error_code and trap_no set for userspace faults and
+                * kernelspace faults which result in die(), but not
+                * kernelspace faults which are fixed up.  die() gives the
+                * process no chance to handle the signal and notice the
+                * kernel fault information, so that won't result in polluting
+                * the information about previously queued, but not yet
+                * delivered, faults.  See also do_general_protection below.
+                */
+               tsk->thread.error_code = error_code;
+               tsk->thread.trap_no = trapnr;
+
                if (info)
                        force_sig_info(signr, info, tsk);
                else
@@ -497,8 +507,11 @@ static void __kprobes do_trap(int trapnr, int signr, char *str, int vm86,
        }
 
        kernel_trap: {
-               if (!fixup_exception(regs))
+               if (!fixup_exception(regs)) {
+                       tsk->thread.error_code = error_code;
+                       tsk->thread.trap_no = trapnr;
                        die(str, regs, error_code);
+               }
                return;
        }
 
@@ -603,9 +616,6 @@ fastcall void __kprobes do_general_protection(struct pt_regs * regs,
        }
        put_cpu();
 
-       current->thread.error_code = error_code;
-       current->thread.trap_no = 13;
-
        if (regs->eflags & VM_MASK)
                goto gp_in_vm86;
 
@@ -624,6 +634,8 @@ gp_in_vm86:
 
 gp_in_kernel:
        if (!fixup_exception(regs)) {
+               current->thread.error_code = error_code;
+               current->thread.trap_no = 13;
                if (notify_die(DIE_GPF, "general protection fault", regs,
                                error_code, 13, SIGSEGV) == NOTIFY_STOP)
                        return;

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 09d2e8a10a496d2dd4c65b19ab7365f5073e2ec0..cceef5bd730269cef8189f3ac33d758d1fbb2e2c 100644 (file)
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -581,10 +581,20 @@ static void __kprobes do_trap(int trapnr, int signr, char *str,
 {
        struct task_struct *tsk = current;
 
-       tsk->thread.error_code = error_code;
-       tsk->thread.trap_no = trapnr;
-
        if (user_mode(regs)) {
+               /*
+                * We want error_code and trap_no set for userspace
+                * faults and kernelspace faults which result in
+                * die(), but not kernelspace faults which are fixed
+                * up.  die() gives the process no chance to handle
+                * the signal and notice the kernel fault information,
+                * so that won't result in polluting the information
+                * about previously queued, but not yet delivered,
+                * faults.  See also do_general_protection below.
+                */
+               tsk->thread.error_code = error_code;
+               tsk->thread.trap_no = trapnr;
+
                if (exception_trace && unhandled_signal(tsk, signr))
                        printk(KERN_INFO
                               "%s[%d] trap %s rip:%lx rsp:%lx error:%lx\n",
@@ -605,8 +615,11 @@ static void __kprobes do_trap(int trapnr, int signr, char *str,
                fixup = search_exception_tables(regs->rip);
                if (fixup)
                        regs->rip = fixup->fixup;
-               else    
+               else {
+                       tsk->thread.error_code = error_code;
+                       tsk->thread.trap_no = trapnr;
                        die(str, regs, error_code);
+               }
                return;
        }
 }
@@ -682,10 +695,10 @@ asmlinkage void __kprobes do_general_protection(struct pt_regs * regs,
 
        conditional_sti(regs);
 
-       tsk->thread.error_code = error_code;
-       tsk->thread.trap_no = 13;
-
        if (user_mode(regs)) {
+               tsk->thread.error_code = error_code;
+               tsk->thread.trap_no = 13;
+
                if (exception_trace && unhandled_signal(tsk, SIGSEGV))
                        printk(KERN_INFO
                       "%s[%d] general protection rip:%lx rsp:%lx error:%lx\n",
@@ -704,6 +717,9 @@ asmlinkage void __kprobes do_general_protection(struct pt_regs * regs,
                        regs->rip = fixup->fixup;
                        return;
                }
+
+               tsk->thread.error_code = error_code;
+               tsk->thread.trap_no = 13;
                if (notify_die(DIE_GPF, "general protection fault", regs,
                                        error_code, 13, SIGSEGV) == NOTIFY_STOP)
                        return;