Messages in this thread | | | Date | Sat, 6 Jun 2020 01:58:06 +0900 | From | Masami Hiramatsu <> | Subject | Re: kprobes string reading broken on s390 |
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Hi Sven,
On Fri, 5 Jun 2020 15:25:41 +0200 Christoph Hellwig <hch@lst.de> wrote:
> Yes, this looks correct. You probably want to write a small changelog > and add a Fixes tag, though. > > On Fri, Jun 05, 2020 at 01:05:34PM +0200, Sven Schnelle wrote: > > Hi Christoph, > > > > with the latest linux-next i noticed that some tests in the > > ftrace test suites are failing on s390, namely: > > > > [FAIL] Kprobe event symbol argument > > [FAIL] Kprobe event with comm arguments > > > > The following doesn't work anymore: > > > > cd /sys/kernel/tracing > > echo 'p:testprobe _do_fork comm=$comm ' >kprobe_events > > echo 1 >/sys/kernel/tracing/events/kprobes/testprobe/enable > > cat /sys/kernel/tracing/trace > > > > it will just show > > > > test.sh-519 [012] .... 18.580625: testprobe: (_do_fork+0x0/0x3c8) comm=(fault) > > > > Looking at d411a9c4e95a ("tracing/kprobes: handle mixed kernel/userspace probes > > better") i see that there are two helpers for reading strings: > > > > fetch_store_string_user() -> read string from user space > > fetch_store_string() -> read string from kernel space(?) > > > > but in the end both are using strncpy_from_user_nofault(), but i would > > think that fetch_store_string() should use strncpy_from_kernel_nofault(). > > However, i'm not sure about the exact semantics of fetch_store_string(), > > as there where a lot of wrong assumptions in the past, especially since > > on x86 you usually don't fail if you use the same function for accessing kernel > > and userspace although it's technically wrong.
Thanks for fixing! This report can be a good changelog. Please resend it with Fixed tag as Christoph said.
Christoph, it seems your series in the akpm tree, so this also should be sent to Andrew?
Thank you,
> > > > Regards, > > Sven > > > > commit 81408eab8fcc79dc0871a95462b13176d3446f5e > > Author: Sven Schnelle <svens@linux.ibm.com> > > Date: Fri Jun 5 13:01:24 2020 +0200 > > > > kprobes: use strncpy_from_kernel_nofault() in fetch_store_string() > > > > Signed-off-by: Sven Schnelle <svens@linux.ibm.com> > > > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > > index b1f21d558e45..ea8d0b094f1b 100644 > > --- a/kernel/trace/trace_kprobe.c > > +++ b/kernel/trace/trace_kprobe.c > > @@ -1278,7 +1278,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base) > > * Try to get string again, since the string can be changed while > > * probing. > > */ > > - ret = strncpy_from_user_nofault(__dest, (void *)addr, maxlen); > > + ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen); > > if (ret >= 0) > > *(u32 *)dest = make_data_loc(ret, __dest - base); > > > ---end quoted text---
-- Masami Hiramatsu <mhiramat@kernel.org>
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