On Thu, 17 Jan 2019 14:44:41 +0100 Andreas Ziegler <andreas.zieg...@fau.de> wrote:
> Hi, > > 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 *base) > >>>> 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; > >>>> break; > >>>> + case FETCH_OP_COMM: > >>>> + val = (unsigned long)current->comm; > >>>> + break; > >>>> case FETCH_OP_FOFFS: > >>>> val = translate_user_vaddr(code->immediate); > >>>> break; > >>> > >>> > >> > > > > > 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? Yes, clearly your patch should go to stable to fix the multiple string support. Mine is only for v4.20. Thank you! > > I added Greg as he might know the answer to that. > > Thanks, > > Andreas > -- Masami Hiramatsu <mhira...@kernel.org>