On 1/17/19 10:47 AM, Masami Hiramatsu wrote:
On Thu, 17 Jan 2019 09:08:41 +0100
Andreas Ziegler <andreas.zieg...@fau.de> wrote:

On 17.01.19 09:00, Masami Hiramatsu wrote:
On Thu, 17 Jan 2019 15:13:09 +0900
Masami Hiramatsu <mhira...@kernel.org> wrote:

On Wed, 16 Jan 2019 11:16:07 +0100
Andreas Ziegler <andreas.zieg...@fau.de> wrote:

I went into this a bit deeper today, and right now it is simply failing
to parse the code because there is no FETCH_OP_COMM case in
process_fetch_insn() for uprobes so that will return -EILSEQ, leading to
a make_data_loc(0, ...) in store_trace_args(). If we just add
FETCH_OP_COMM and let val point to current->comm (that's what
trace_kprobe.c does), we get an -EFAULT return value from
fetch_store_string because strncpy_from_user() checks if the argument is
in user space.

Correct. I missed to add OP_COMM support. And uprobe's fetch_store_string
is only for user space strings.

So I think we might need a special case for that, something like
FETCH_OP_ST_COMM_STRING which is only used for FETCH_OP_COMM and copies
current->comm over to the dynamic area. The implementation could be
similar to the old fetch_comm_string implementation before your rewrite.

Hmm, instead, I would like to add current->comm checker and only allows
to copy that. That would be simpler and enough.

Could you test below patch?

tracing: uprobes: Re-enable $comm support for uprobe events

From: Masami Hiramatsu <mhira...@kernel.org>

Since commit 533059281ee5 ("tracing: probeevent: Introduce new
argument fetching code") dropped the $comm support from uprobe
events, this re-enable it.

this should read 're-enables'.

For $comm support, use strncpy() instead of strncpy_from_user()
we're using strlcpy(), not strncpy().

to copy current task's comm. Because it is in the kernel space,
strncpy_from_user() always fails to copy the comm.
This also use strlen() instead of strlen_user() to measure the
                ^                        ^
'uses', and the function should be 'strnlen_user()'.

length of the comm.

Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
Reported-by: Andreas Ziegler <andreas.zieg...@fau.de>
  kernel/trace/trace_uprobe.c |   13 +++++++++++--
  1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index e335576b9411..97d134e83e0f 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -156,7 +156,10 @@ fetch_store_string(unsigned long addr, void *dest, void 
        if (unlikely(!maxlen))
                return -ENOMEM;
- ret = strncpy_from_user(dst, src, maxlen);
+       if (addr == (unsigned long)current->comm)
+               ret = strlcpy(dst, current->comm, maxlen);
+       else
+               ret = strncpy_from_user(dst, src, maxlen);
        if (ret >= 0) {
                if (ret == maxlen)
                        dst[ret - 1] = '\0';
@@ -173,7 +176,10 @@ fetch_store_strlen(unsigned long addr)
        int len;
        void __user *vaddr = (void __force __user *) addr;
- len = strnlen_user(vaddr, MAX_STRING_SIZE);
+       if (addr == (unsigned long)current->comm)
+               len = strlen(current->comm);

To balance with the strnlen_user, we must increse the len in this block.
(strlen doesn't count the final '\0', but strnlen_user counts it)

yes, we need to add a '+ 1' here.

With the typos and this one fixed, this is

Acked-by: Andreas Ziegler <andreas.zieg...@fau.de>

Thank you for fixing typo and Ack :)

Thanks you,

Thank you,

+       else
+               len = strnlen_user(vaddr, MAX_STRING_SIZE);
return (len > MAX_STRING_SIZE) ? 0 : len;
@@ -213,6 +219,9 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs 
*regs, void *dest,
        case FETCH_OP_IMM:
                val = code->immediate;
+       case FETCH_OP_COMM:
+               val = (unsigned long)current->comm;
+               break;
        case FETCH_OP_FOFFS:
                val = translate_user_vaddr(code->immediate);

as the original commit breaking $comm support was merged for v4.20 (which is a stable kernel) and the wrong behaviour with multiple strings exists in all longterm/stable releases (tested back to v4.4), do you think this should be going into a stable release once it's merged?

I added Greg as he might know the answer to that.



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