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 <[email protected]>
> Date: Fri Jun 5 13:01:24 2020 +0200
>
> kprobes: use strncpy_from_kernel_nofault() in fetch_store_string()
>
> Signed-off-by: Sven Schnelle <[email protected]>
>
> 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);
>
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