* [PATCH] um: Fix kcov crash before kernel is started.
@ 2017-10-08 10:31 Thomas Meyer
2017-10-08 10:44 ` Richard Weinberger
0 siblings, 1 reply; 5+ messages in thread
From: Thomas Meyer @ 2017-10-08 10:31 UTC (permalink / raw)
To: user-mode-linux-devel, linux-kernel, richard; +Cc: Thomas Meyer
UMLs current_thread_info() unconditionally assumes that the top of the stack
contains the thread_info structure. But on UML the __sanitizer_cov_trace_pc
function is called for *all* functions! This results in an early crash:
Prevent kcov from using invalid curent_thread_info() data by checking
the system_state.
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
---
kernel/kcov.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/kcov.c b/kernel/kcov.c
index 3f693a0f6f3e..d601c0e956f6 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -56,6 +56,12 @@ void notrace __sanitizer_cov_trace_pc(void)
struct task_struct *t;
enum kcov_mode mode;
+#ifdef CONFIG_UML
+ if(!(system_state == SYSTEM_SCHEDULING ||
+ system_state == SYSTEM_RUNNING))
+ return;
+#endif
+
t = current;
/*
* We are interested in code coverage as a function of a syscall inputs,
--
2.11.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] um: Fix kcov crash before kernel is started.
2017-10-08 10:31 [PATCH] um: Fix kcov crash before kernel is started Thomas Meyer
@ 2017-10-08 10:44 ` Richard Weinberger
2017-10-08 11:18 ` Thomas Meyer
0 siblings, 1 reply; 5+ messages in thread
From: Richard Weinberger @ 2017-10-08 10:44 UTC (permalink / raw)
To: Thomas Meyer; +Cc: user-mode-linux-devel, linux-kernel
Am Sonntag, 8. Oktober 2017, 12:31:58 CEST schrieb Thomas Meyer:
> UMLs current_thread_info() unconditionally assumes that the top of the stack
> contains the thread_info structure. But on UML the __sanitizer_cov_trace_pc
> function is called for *all* functions! This results in an early crash:
>
> Prevent kcov from using invalid curent_thread_info() data by checking
> the system_state.
>
> Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
> ---
> kernel/kcov.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 3f693a0f6f3e..d601c0e956f6 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -56,6 +56,12 @@ void notrace __sanitizer_cov_trace_pc(void)
> struct task_struct *t;
> enum kcov_mode mode;
>
> +#ifdef CONFIG_UML
> + if(!(system_state == SYSTEM_SCHEDULING ||
> + system_state == SYSTEM_RUNNING))
> + return;
> +#endif
Hmm, and why does it work on all other archs then?
Thanks,
//richard
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] um: Fix kcov crash before kernel is started.
2017-10-08 10:44 ` Richard Weinberger
@ 2017-10-08 11:18 ` Thomas Meyer
0 siblings, 0 replies; 5+ messages in thread
From: Thomas Meyer @ 2017-10-08 11:18 UTC (permalink / raw)
To: Richard Weinberger; +Cc: user-mode-linux-devel, linux-kernel
On Sun, Oct 08, 2017 at 12:44:12PM +0200, Richard Weinberger wrote:
> Am Sonntag, 8. Oktober 2017, 12:31:58 CEST schrieb Thomas Meyer:
> > UMLs current_thread_info() unconditionally assumes that the top of the stack
> > contains the thread_info structure. But on UML the __sanitizer_cov_trace_pc
> > function is called for *all* functions! This results in an early crash:
> >
> > Prevent kcov from using invalid curent_thread_info() data by checking
> > the system_state.
> >
> > Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
> > ---
> > kernel/kcov.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/kernel/kcov.c b/kernel/kcov.c
> > index 3f693a0f6f3e..d601c0e956f6 100644
> > --- a/kernel/kcov.c
> > +++ b/kernel/kcov.c
> > @@ -56,6 +56,12 @@ void notrace __sanitizer_cov_trace_pc(void)
> > struct task_struct *t;
> > enum kcov_mode mode;
> >
> > +#ifdef CONFIG_UML
> > + if(!(system_state == SYSTEM_SCHEDULING ||
> > + system_state == SYSTEM_RUNNING))
> > + return;
> > +#endif
>
> Hmm, and why does it work on all other archs then?
Hi,
I guess UML is different then other archs! But to be honest I'm not sure
why. I assume that __sanitizer_cov_trace_pc on other archs isn't called
that early, or that curent_thread_info returns NULL on other archs when
the first task isn't running yet.
But as I fail to use/setup the qemu gdb attachment to debug early x86_64 code
I can't say exactly why.
Maybe someone how knows the inner workings of x86_64 and/or kcov can
answer this question!
>
> Thanks,
> //richard
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] um: Fix kcov crash before kernel is started.
2017-10-13 22:00 ` [PATCH] um: Fix kcov crash before kernel is started Thomas Meyer
@ 2017-10-14 8:05 ` Richard Weinberger
0 siblings, 0 replies; 5+ messages in thread
From: Richard Weinberger @ 2017-10-14 8:05 UTC (permalink / raw)
To: Thomas Meyer; +Cc: syzkaller, user-mode-linux-devel, linux-kernel
Am Samstag, 14. Oktober 2017, 00:00:25 CEST schrieb Thomas Meyer:
> UMLs current_thread_info() unconditionally assumes that the top of the stack
> contains the thread_info structure.
> Prevent kcov from using invalid curent_thread_info() data by disable
> instrumentation of early startup code.
>
> Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
> ---
> arch/um/kernel/skas/Makefile | 2 ++
> lib/Makefile | 4 ++++
> 2 files changed, 6 insertions(+)
>
> diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
> index 0b76d8869c94..df3aedb974a2 100644
> --- a/arch/um/kernel/skas/Makefile
> +++ b/arch/um/kernel/skas/Makefile
> @@ -3,6 +3,8 @@
> # Licensed under the GPL
> #
>
> +KCOV_INSTRUMENT := n
So, you disable kconv for the whole SKAS code?
That's a bit broad. ;-\
> obj-y := clone.o mmu.o process.o syscall.o uaccess.o
>
> # clone.o is in the stub, so it can't be built with profiling
> diff --git a/lib/Makefile b/lib/Makefile
> index dafa79613fb4..18319ad5daab 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -16,6 +16,10 @@ KCOV_INSTRUMENT_list_debug.o := n
> KCOV_INSTRUMENT_debugobjects.o := n
> KCOV_INSTRUMENT_dynamic_debug.o := n
>
> +ifdef CONFIG_UML
> +KCOV_INSTRUMENT_cmdline.o := n
> +endif
> +
huh? Why do we need an exception for UML here?
Thanks,
//richard
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] um: Fix kcov crash before kernel is started.
2017-10-10 8:59 [thomas@m3y3r.de: Re: [PATCH] um: Fix kcov crash before kernel is started.] Dmitry Vyukov
@ 2017-10-13 22:00 ` Thomas Meyer
2017-10-14 8:05 ` Richard Weinberger
0 siblings, 1 reply; 5+ messages in thread
From: Thomas Meyer @ 2017-10-13 22:00 UTC (permalink / raw)
To: syzkaller, richard, user-mode-linux-devel, linux-kernel; +Cc: Thomas Meyer
UMLs current_thread_info() unconditionally assumes that the top of the stack
contains the thread_info structure.
Prevent kcov from using invalid curent_thread_info() data by disable
instrumentation of early startup code.
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
---
arch/um/kernel/skas/Makefile | 2 ++
lib/Makefile | 4 ++++
2 files changed, 6 insertions(+)
diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
index 0b76d8869c94..df3aedb974a2 100644
--- a/arch/um/kernel/skas/Makefile
+++ b/arch/um/kernel/skas/Makefile
@@ -3,6 +3,8 @@
# Licensed under the GPL
#
+KCOV_INSTRUMENT := n
+
obj-y := clone.o mmu.o process.o syscall.o uaccess.o
# clone.o is in the stub, so it can't be built with profiling
diff --git a/lib/Makefile b/lib/Makefile
index dafa79613fb4..18319ad5daab 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -16,6 +16,10 @@ KCOV_INSTRUMENT_list_debug.o := n
KCOV_INSTRUMENT_debugobjects.o := n
KCOV_INSTRUMENT_dynamic_debug.o := n
+ifdef CONFIG_UML
+KCOV_INSTRUMENT_cmdline.o := n
+endif
+
lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o dump_stack.o timerqueue.o\
idr.o int_sqrt.o extable.o \
--
2.11.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2017-10-08 10:31 [PATCH] um: Fix kcov crash before kernel is started Thomas Meyer
2017-10-08 10:44 ` Richard Weinberger
2017-10-08 11:18 ` Thomas Meyer
2017-10-10 8:59 [thomas@m3y3r.de: Re: [PATCH] um: Fix kcov crash before kernel is started.] Dmitry Vyukov
2017-10-13 22:00 ` [PATCH] um: Fix kcov crash before kernel is started Thomas Meyer
2017-10-14 8:05 ` Richard Weinberger
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