Messages in this thread | | | Date | Fri, 5 Jun 2020 15:25:41 +0200 | From | Christoph Hellwig <> | Subject | Re: kprobes string reading broken on s390 |
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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. > > 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---
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