From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: David Laight <David.Laight@aculab.com>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-integrity@vger.kernel.org"
<linux-integrity@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>,
"oleg@redhat.com" <oleg@redhat.com>,
"x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor
Date: Tue, 28 Jul 2020 12:39:59 -0500 [thread overview]
Message-ID: <81d744c0-923e-35ad-6063-8b186f6a153c@linux.microsoft.com> (raw)
In-Reply-To: <CALCETrUta5-0TLJ9-jfdehpTAp2Efmukk2npYadFzz9ozOrG2w@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 3416 bytes --]
On 7/28/20 12:16 PM, Andy Lutomirski wrote:
> On Tue, Jul 28, 2020 at 9:32 AM Madhavan T. Venkataraman
> <madvenka@linux.microsoft.com> wrote:
>> Thanks. See inline..
>>
>> On 7/28/20 10:13 AM, David Laight wrote:
>>> From: madvenka@linux.microsoft.com
>>>> Sent: 28 July 2020 14:11
>>> ...
>>>> The kernel creates the trampoline mapping without any permissions. When
>>>> the trampoline is executed by user code, a page fault happens and the
>>>> kernel gets control. The kernel recognizes that this is a trampoline
>>>> invocation. It sets up the user registers based on the specified
>>>> register context, and/or pushes values on the user stack based on the
>>>> specified stack context, and sets the user PC to the requested target
>>>> PC. When the kernel returns, execution continues at the target PC.
>>>> So, the kernel does the work of the trampoline on behalf of the
>>>> application.
>>> Isn't the performance of this going to be horrid?
>> It takes about the same amount of time as getpid(). So, it is
>> one quick trip into the kernel. I expect that applications will
>> typically not care about this extra overhead as long as
>> they are able to run.
> What did you test this on? A page fault on any modern x86_64 system
> is much, much, much, much slower than a syscall.
I tested it in on a KVM guest running Ubuntu. So, when you say
that a page fault is much slower, do you mean a regular page
fault that is handled through the VM layer? Here is the relevant code
in do_user_addr_fault():
if (unlikely(access_error(hw_error_code, vma))) {
/*
* If it is a user execute fault, it could be a trampoline
* invocation.
*/
if ((hw_error_code & tflags) == tflags &&
trampfd_fault(vma, regs)) {
up_read(&mm->mmap_sem);
return;
}
bad_area_access_error(regs, hw_error_code, address, vma);
return;
}
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
* the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
* we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
*
* Note that handle_userfault() may also release and reacquire mmap_sem
* (and not return with VM_FAULT_RETRY), when returning to userland to
* repeat the page fault later with a VM_FAULT_NOPAGE retval
* (potentially after handling any pending signal during the return to
* userland). The return to userland is identified whenever
* FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
*/
fault = handle_mm_fault(vma, address, flags);
trampfd faults are instruction faults that go through a different code
path than the one that calls handle_mm_fault().
Could you clarify?
Thanks.
Madhavan
[-- Attachment #2: Type: text/html, Size: 5712 bytes --]
next prev parent reply other threads:[~2020-07-28 17:40 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <aefc85852ea518982e74b233e11e16d2e707bc32>
2020-07-28 13:10 ` [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor madvenka
2020-07-28 13:10 ` [PATCH v1 1/4] [RFC] fs/trampfd: Implement the trampoline file descriptor API madvenka
2020-07-28 14:50 ` Oleg Nesterov
2020-07-28 14:58 ` Madhavan T. Venkataraman
2020-07-28 16:06 ` Oleg Nesterov
2020-07-28 13:10 ` [PATCH v1 2/4] [RFC] x86/trampfd: Provide support for the trampoline file descriptor madvenka
2020-07-30 9:06 ` Greg KH
2020-07-30 14:25 ` Madhavan T. Venkataraman
2020-07-28 13:10 ` [PATCH v1 3/4] [RFC] arm64/trampfd: " madvenka
2020-07-28 13:10 ` [PATCH v1 4/4] [RFC] arm/trampfd: " madvenka
2020-07-28 15:13 ` [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor David Laight
2020-07-28 16:32 ` Madhavan T. Venkataraman
2020-07-28 17:16 ` Andy Lutomirski
2020-07-28 17:39 ` Madhavan T. Venkataraman [this message]
2020-07-29 5:16 ` Andy Lutomirski
2020-07-28 18:52 ` Madhavan T. Venkataraman
2020-07-29 8:36 ` David Laight
2020-07-29 17:55 ` Madhavan T. Venkataraman
2020-07-28 16:05 ` Casey Schaufler
2020-07-28 16:49 ` Madhavan T. Venkataraman
2020-07-28 17:05 ` James Morris
2020-07-28 17:08 ` Madhavan T. Venkataraman
2020-07-28 17:31 ` Andy Lutomirski
2020-07-28 19:01 ` Madhavan T. Venkataraman
2020-07-29 13:29 ` Florian Weimer
2020-07-30 13:09 ` David Laight
2020-08-02 11:56 ` Pavel Machek
2020-08-03 8:08 ` David Laight
2020-08-03 15:57 ` Madhavan T. Venkataraman
2020-07-30 14:24 ` Madhavan T. Venkataraman
2020-07-30 20:54 ` Andy Lutomirski
2020-07-31 17:13 ` Madhavan T. Venkataraman
2020-07-31 18:31 ` Mark Rutland
2020-08-03 8:27 ` David Laight
2020-08-03 16:03 ` Madhavan T. Venkataraman
2020-08-03 16:57 ` David Laight
2020-08-03 17:00 ` Madhavan T. Venkataraman
2020-08-03 17:58 ` Madhavan T. Venkataraman
2020-08-04 13:55 ` Mark Rutland
2020-08-04 14:33 ` David Laight
2020-08-04 14:44 ` David Laight
2020-08-04 14:48 ` Madhavan T. Venkataraman
2020-08-04 15:46 ` Madhavan T. Venkataraman
2020-08-02 13:57 ` Florian Weimer
2020-07-30 14:42 ` Madhavan T. Venkataraman
2020-08-02 18:54 ` Madhavan T. Venkataraman
2020-08-02 20:00 ` Andy Lutomirski
2020-08-02 22:58 ` Madhavan T. Venkataraman
2020-08-03 18:36 ` Madhavan T. Venkataraman
2020-08-10 17:20 ` Madhavan T. Venkataraman
2020-08-10 17:34 ` Madhavan T. Venkataraman
2020-08-11 21:12 ` Madhavan T. Venkataraman
2020-08-03 8:23 ` David Laight
2020-08-03 15:59 ` Madhavan T. Venkataraman
2020-07-31 18:09 ` Mark Rutland
2020-07-31 20:08 ` Madhavan T. Venkataraman
2020-08-03 16:57 ` Madhavan T. Venkataraman
2020-08-04 14:30 ` Mark Rutland
2020-08-06 17:26 ` Madhavan T. Venkataraman
2020-08-08 22:17 ` Pavel Machek
2020-08-11 12:41 ` Madhavan T. Venkataraman
2020-08-11 13:08 ` Pavel Machek
2020-08-11 15:54 ` Madhavan T. Venkataraman
2020-08-12 10:06 ` Mark Rutland
2020-08-12 18:47 ` Madhavan T. Venkataraman
2020-08-19 18:53 ` Mickaël Salaün
2020-09-01 15:42 ` Mark Rutland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=81d744c0-923e-35ad-6063-8b186f6a153c@linux.microsoft.com \
--to=madvenka@linux.microsoft.com \
--cc=David.Laight@aculab.com \
--cc=kernel-hardening@lists.openwall.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=luto@kernel.org \
--cc=oleg@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).