Messages in this thread Patch in this message | | | Date | Thu, 13 Jan 2022 12:57:54 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] tracing: Add test for user space strings when filtering on string pointers |
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On Tue, 11 Jan 2022 21:55:53 +0100 Sven Schnelle <svens@linux.ibm.com> wrote:
> > Isn't there also at least one architecture where you can't differentiate > > between user and kernel pointers by looking at the address? > > (Something like sparc ASI is used for user accesses so both user > > and kernel get the full 4G address range. But it isn't sparc (or pdp/11)) > > ISTR it causing issues with the code for kernel_setsockopt() and > > required a separate flag. > > On s390 TASK_SIZE is defined as -PAGE_SIZE, so with the patch above the > kernel would always try to fetch it from user space. I think it would be > the same for parisc.
As a work around for these cases, would something like this work?
-- Steve
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index 91352a64be09..06013822764c 100644 --- a/kernel/trace/trace_events_filter.c +++ b/kernel/trace/trace_events_filter.c @@ -676,7 +676,15 @@ static __always_inline char *test_string(char *str) ubuf = this_cpu_ptr(ustring_per_cpu); kstr = ubuf->buffer; - if (likely((unsigned long)str >= TASK_SIZE)) { + /* + * Test the address of ustring_per_cpu against TASK_SIZE, as + * comparing TASK_SIZE to determine kernel/user space address + * is not enough on some architectures. If the address is less + * than TASK_SIZE we know this is the case, in which we should + * always use the from_kernel variant. + */ + if ((unsigned long)&ustring_per_cpu < (unsigned long)TASK_SIZE || + likely((unsigned long)str >= TASK_SIZE)) { /* For safety, do not trust the string pointer */ if (!strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE)) return NULL;
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