From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Sebastian Mayr <me@sam.st>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: get_unmapped_area && in_ia32_syscall (Was: [PATCH] uprobes/x86: fix detection of 32-bit user mode)
Date: Wed, 28 Aug 2019 13:37:43 +0200 [thread overview]
Message-ID: <20190828113743.GA3721@redhat.com> (raw)
In-Reply-To: <459fdf33-1290-2651-6344-0ff9e466ddfc@gmail.com>
On 08/28, Dmitry Safonov wrote:
>
> > On 8/27/19 3:00 PM, Oleg Nesterov wrote:
> > [..]
> >> But to remind, there is another problem with in_ia32_syscall() && uprobes.
> >>
> >> get_unmapped_area() paths use in_ia32_syscall() and this is wrong in case
> >> when the caller is xol_add_vma(), in this case TS_COMPAT won't be set.>
> >> Usually the addr = TASK_SIZE - PAGE_SIZE passed to get_unmapped_area() should
> >> work, mm->get_unmapped_area() won't be even called. But if this addr is already
> >> occupied get_area() can return addr > TASK_SIZE.
> >
> > Technically, it's not bigger than TASK_SIZE that's supplied
> > get_unmapped_area() as an argument..
Hmm. What do you mean?
Just in case, TASK_SIZE checks TIF_ADDR32, not TS_COMPAT.
> >> if (!area->vaddr) {
> >> + if(!is_64bit_mm(mm))
> >> + current_thread_info()->status |= TS_COMPAT;
> >> /* Try to map as high as possible, this is only a hint. */
> >> area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
> >> PAGE_SIZE, 0, 0);
> >> + if(!is_64bit_mm(mm))
> >> + current_thread_info()->status &= ~TS_COMPAT;;
> >> if (area->vaddr & ~PAGE_MASK) {
> >> ret = area->vaddr;
> >> goto fail;
> >
> > It could have been TASK_SIZE_OF(),
tsk is always current, why do we need TASK_SIZE_OF() ?
> > I see that arch_uprobe_analyze_insn() uses is_64bit_mm() which
> > is correct the majority of time, but not for processes those jump
> > switching CS..
Heh. it's actually even worse. Just suppose a 32-bit application simply
mmaps a 64-bit executable which has a probe. But this is off-topic.
> > Do I read the code properly and xol is always one page?
Yes,
> > Could that page be reserved on the top of mmap_base/mmap_compat_base at
> > the binfmt loading time?
How? I don't understand...
> (I would need than to add .mremap() for
> > restoring sake).
for what? I don't think you can restore a probed process anyway... OK,
right now this is off-topic too.
Oleg.
next prev parent reply other threads:[~2019-08-28 11:37 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-28 15:26 [PATCH] uprobes/x86: fix detection of 32-bit user mode Sebastian Mayr
2019-08-19 18:40 ` Sebastian Mayr
2019-08-19 18:43 ` Thomas Gleixner
2019-08-23 23:30 ` Thomas Gleixner
2019-08-23 23:44 ` Thomas Gleixner
2019-08-23 23:57 ` Andy Lutomirski
2019-08-24 0:00 ` Thomas Gleixner
2019-08-24 0:03 ` Thomas Gleixner
2019-08-24 0:13 ` Andy Lutomirski
2019-08-24 0:20 ` Thomas Gleixner
2019-08-26 13:48 ` Thomas Gleixner
2019-08-27 14:00 ` get_unmapped_area && in_ia32_syscall (Was: [PATCH] uprobes/x86: fix detection of 32-bit user mode) Oleg Nesterov
2019-08-27 17:03 ` Dmitry Safonov
2019-08-27 23:40 ` Dmitry Safonov
2019-08-28 11:37 ` Oleg Nesterov [this message]
2019-08-26 14:02 ` [tip: x86/urgent] uprobes/x86: Fix detection of 32-bit user mode tip-bot2 for Sebastian Mayr
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