* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
@ 2007-02-13 7:52 Jan Beulich
2007-02-13 10:00 ` Andi Kleen
2007-02-14 17:51 ` Jeff Dike
0 siblings, 2 replies; 8+ messages in thread
From: Jan Beulich @ 2007-02-13 7:52 UTC (permalink / raw)
To: Jeff Dike; +Cc: Andi Kleen, linux-kernel, patches
>Yup. How does this patch look to you? We set error_code and trap_no
>for userspace faults and kernel faults which call die(). We don't set
>them for kernelspace faults which are fixed up.
Actually, after a second round of thinking I believe there's still more to do
- your second patch missed fixing i386's do_trap() similarly to x86-64's
and, vice versa, x86-64's do_general_protection() similarly to i386's.
Jan
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-13 7:52 [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead Jan Beulich
@ 2007-02-13 10:00 ` Andi Kleen
2007-02-14 17:51 ` Jeff Dike
1 sibling, 0 replies; 8+ messages in thread
From: Andi Kleen @ 2007-02-13 10:00 UTC (permalink / raw)
To: Jan Beulich; +Cc: Jeff Dike, linux-kernel, patches
On Tuesday 13 February 2007 08:52, Jan Beulich wrote:
> >Yup. How does this patch look to you? We set error_code and trap_no
> >for userspace faults and kernel faults which call die(). We don't set
> >them for kernelspace faults which are fixed up.
>
> Actually, after a second round of thinking I believe there's still more to do
> - your second patch missed fixing i386's do_trap() similarly to x86-64's
> and, vice versa, x86-64's do_general_protection() similarly to i386's.
I dropped the patch for now until that is all worked out
-Andi
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-13 7:52 [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead Jan Beulich
2007-02-13 10:00 ` Andi Kleen
@ 2007-02-14 17:51 ` Jeff Dike
2007-02-15 8:01 ` Jan Beulich
1 sibling, 1 reply; 8+ messages in thread
From: Jeff Dike @ 2007-02-14 17:51 UTC (permalink / raw)
To: Jan Beulich; +Cc: Andi Kleen, linux-kernel, patches
On Tue, Feb 13, 2007 at 07:52:54AM +0000, Jan Beulich wrote:
> Actually, after a second round of thinking I believe there's still more to do
> - your second patch missed fixing i386's do_trap() similarly to x86-64's
> and, vice versa, x86-64's do_general_protection() similarly to i386's.
Sigh, here's another go at it - the full patch instead of
incrementally fixing the old one:
Index: linux-2.6/arch/i386/kernel/traps.c
===================================================================
--- linux-2.6.orig/arch/i386/kernel/traps.c
+++ linux-2.6/arch/i386/kernel/traps.c
@@ -473,8 +473,6 @@ static void __kprobes do_trap(int trapnr
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)
@@ -486,6 +484,9 @@ static void __kprobes do_trap(int trapnr
goto kernel_trap;
trap_signal: {
+ tsk->thread.error_code = error_code;
+ tsk->thread.trap_no = trapnr;
+
if (info)
force_sig_info(signr, info, tsk);
else
@@ -494,8 +495,11 @@ static void __kprobes do_trap(int trapnr
}
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;
}
@@ -600,15 +604,21 @@ fastcall void __kprobes do_general_prote
}
put_cpu();
- current->thread.error_code = error_code;
- current->thread.trap_no = 13;
-
if (regs->eflags & VM_MASK)
goto gp_in_vm86;
if (!user_mode(regs))
goto gp_in_kernel;
+ /*
+ * 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, fault.
+ */
current->thread.error_code = error_code;
current->thread.trap_no = 13;
force_sig(SIGSEGV, current);
@@ -621,6 +631,8 @@ 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;
Index: linux-2.6/arch/x86_64/kernel/traps.c
===================================================================
--- linux-2.6.orig/arch/x86_64/kernel/traps.c
+++ linux-2.6/arch/x86_64/kernel/traps.c
@@ -581,10 +581,19 @@ static void __kprobes do_trap(int trapnr
{
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, fault.
+ */
+ 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 +614,11 @@ static void __kprobes do_trap(int trapnr
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 +694,10 @@ asmlinkage void __kprobes do_general_pro
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 +716,10 @@ asmlinkage void __kprobes do_general_pro
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;
--
Work email - jdike at linux dot intel dot com
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-14 17:51 ` Jeff Dike
@ 2007-02-15 8:01 ` Jan Beulich
2007-02-15 16:23 ` Jeff Dike
0 siblings, 1 reply; 8+ messages in thread
From: Jan Beulich @ 2007-02-15 8:01 UTC (permalink / raw)
To: Jeff Dike; +Cc: Andi Kleen, linux-kernel, patches
>>> Jeff Dike <jdike@addtoit.com> 14.02.07 18:51 >>>
>On Tue, Feb 13, 2007 at 07:52:54AM +0000, Jan Beulich wrote:
>> Actually, after a second round of thinking I believe there's still more to do
>> - your second patch missed fixing i386's do_trap() similarly to x86-64's
>> and, vice versa, x86-64's do_general_protection() similarly to i386's.
>
>Sigh, here's another go at it - the full patch instead of
>incrementally fixing the old one:
Ack.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-15 8:01 ` Jan Beulich
@ 2007-02-15 16:23 ` Jeff Dike
0 siblings, 0 replies; 8+ messages in thread
From: Jeff Dike @ 2007-02-15 16:23 UTC (permalink / raw)
To: Jan Beulich; +Cc: Andi Kleen, linux-kernel, patches
On Thu, Feb 15, 2007 at 08:01:20AM +0000, Jan Beulich wrote:
> Ack.
Great, thanks for your help.
Jeff
--
Work email - jdike at linux dot intel dot com
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-12 16:42 ` Jeff Dike
@ 2007-02-12 17:01 ` Jan Beulich
0 siblings, 0 replies; 8+ messages in thread
From: Jan Beulich @ 2007-02-12 17:01 UTC (permalink / raw)
To: Jeff Dike; +Cc: Andi Kleen, linux-kernel, patches
>Yup. How does this patch look to you? We set error_code and trap_no
>for userspace faults and kernel faults which call die(). We don't set
>them for kernelspace faults which are fixed up.
That seems a reasonable approach.
Thanks, Jan
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-12 9:32 ` [patches] " Jan Beulich
@ 2007-02-12 16:42 ` Jeff Dike
2007-02-12 17:01 ` Jan Beulich
0 siblings, 1 reply; 8+ messages in thread
From: Jeff Dike @ 2007-02-12 16:42 UTC (permalink / raw)
To: Jan Beulich; +Cc: Andi Kleen, linux-kernel, patches
On Mon, Feb 12, 2007 at 09:32:10AM +0000, Jan Beulich wrote:
> This breaks consumers of notify_die() relying on the proper trap number being
> passed, as the call to notify_die() from die() currently reads
> current->thread.trap_no.
Rats, good point.
> Also, you seem to leave other places where trap_no gets set untouched -
> is this intentional (do_debug - probably correct here, kernel_math_error -
> probably incorrect here)?
I did check the other trap handlers. kernel_math_error calls die,
which calls do_exit(SIGSEGV). This doesn't seem to allow the process
the opportunity to trap the SIGSEGV and examine the fault information.
> >I looked at i386, and there is a similar situation. In this case, there is
> >duplicate code setting task->thread.error_code and trapno. I deleted one,
> >leaving the copy that runs in the case of a userspace fault.
>
> Likewise.
Yup. How does this patch look to you? We set error_code and trap_no
for userspace faults and kernel faults which call die(). We don't set
them for kernelspace faults which are fixed up.
Index: linux-2.6/arch/i386/kernel/traps.c
===================================================================
--- linux-2.6.orig/arch/i386/kernel/traps.c
+++ linux-2.6/arch/i386/kernel/traps.c
@@ -619,6 +619,8 @@ 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;
Index: linux-2.6/arch/x86_64/kernel/traps.c
===================================================================
--- linux-2.6.orig/arch/x86_64/kernel/traps.c
+++ linux-2.6/arch/x86_64/kernel/traps.c
@@ -605,8 +605,11 @@ static void __kprobes do_trap(int trapnr
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;
}
}
--
Work email - jdike at linux dot intel dot com
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead
2007-02-10 11:50 ` [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead Andi Kleen
@ 2007-02-12 9:32 ` Jan Beulich
2007-02-12 16:42 ` Jeff Dike
0 siblings, 1 reply; 8+ messages in thread
From: Jan Beulich @ 2007-02-12 9:32 UTC (permalink / raw)
To: Jeff Dike, Andi Kleen; +Cc: linux-kernel, patches
>>> Andi Kleen <ak@suse.de> 10.02.07 12:50 >>>
>
>From: Jeff Dike <jdike@addtoit.com>
>
>Kernel-mode traps on x86_64 can pollute the trap information for a previous
>userspace trap for which the signal has not yet been delivered to the
>process.
>
>do_trap and do_general_protection set task->thread.error_code and .trapno
>for kernel traps. If a kernel-mode trap arrives between the arrival of a
>userspace trap and the delivery of the associated SISGEGV to the process,
>the process will get the kernel trap information in its sigcontext.
>
>This causes UML process segfaults, as the trapno that the UML kernel sees
>is 13, rather than the 14 for normal page faults. So, the UML kernel
>passes the SIGSEGV along to its process.
>
>I don't claim to fully understand the problem. On the one hand, a check in
>do_general_protection for a pending SIGSEGV turned up nothing. On the
>other hand, this patch fixed the UML process segfault problem.
>
>The patch below moves the setting of error_code and trapno so that that
>only happens in the case of userspace faults. As a side-effect, this
>should speed up kernel-mode fault handling a tiny bit.
This breaks consumers of notify_die() relying on the proper trap number being
passed, as the call to notify_die() from die() currently reads
current->thread.trap_no.
Also, you seem to leave other places where trap_no gets set untouched -
is this intentional (do_debug - probably correct here, kernel_math_error -
probably incorrect here)?
>I looked at i386, and there is a similar situation. In this case, there is
>duplicate code setting task->thread.error_code and trapno. I deleted one,
>leaving the copy that runs in the case of a userspace fault.
Likewise.
Jan
^ permalink raw reply [flat|nested] 8+ messages in thread
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2007-02-13 7:52 [patches] [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead Jan Beulich
2007-02-13 10:00 ` Andi Kleen
2007-02-14 17:51 ` Jeff Dike
2007-02-15 8:01 ` Jan Beulich
2007-02-15 16:23 ` Jeff Dike
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2007-02-10 11:50 [PATCH 2.6.21 review I] [1/25] x86_64: Add __copy_from_user_nocache Andi Kleen
2007-02-10 11:50 ` [PATCH 2.6.21 review I] [4/25] x86: kernel-mode faults pollute current->thead Andi Kleen
2007-02-12 9:32 ` [patches] " Jan Beulich
2007-02-12 16:42 ` Jeff Dike
2007-02-12 17:01 ` Jan Beulich
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