From: Jeremy Linton <jeremy.linton@arm.com>
To: Dave Martin <Dave.Martin@arm.com>, Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
systemd-devel@lists.freedesktop.org,
Kees Cook <keescook@chromium.org>,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>,
toiwoton@gmail.com, libc-alpha@sourceware.org,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures
Date: Mon, 26 Oct 2020 17:39:42 -0500 [thread overview]
Message-ID: <45c64b49-a38b-4b0c-d9cf-6c586dacbcc9@arm.com> (raw)
In-Reply-To: <20201026175230.GC27285@arm.com>
Hi,
On 10/26/20 12:52 PM, Dave Martin wrote:
> On Mon, Oct 26, 2020 at 04:57:55PM +0000, Szabolcs Nagy via Libc-alpha wrote:
>> The 10/26/2020 16:24, Dave Martin via Libc-alpha wrote:
>>> Unrolling this discussion a bit, this problem comes from a few sources:
>>>
>>> 1) systemd is trying to implement a policy that doesn't fit SECCOMP
>>> syscall filtering very well.
>>>
>>> 2) The program is trying to do something not expressible through the
>>> syscall interface: really the intent is to set PROT_BTI on the page,
>>> with no intent to set PROT_EXEC on any page that didn't already have it
>>> set.
>>>
>>>
>>> This limitation of mprotect() was known when I originally added PROT_BTI,
>>> but at that time we weren't aware of a clear use case that would fail.
>>>
>>>
>>> Would it now help to add something like:
>>>
>>> int mchangeprot(void *addr, size_t len, int old_flags, int new_flags)
>>> {
>>> int ret = -EINVAL;
>>> mmap_write_lock(current->mm);
>>> if (all vmas in [addr .. addr + len) have
>>> their mprotect flags set to old_flags) {
>>>
>>> ret = mprotect(addr, len, new_flags);
>>> }
>>>
>>> mmap_write_unlock(current->mm);
>>> return ret;
>>> }
>>
>> if more prot flags are introduced then the exact
>> match for old_flags may be restrictive and currently
>> there is no way to query these flags to figure out
>> how to toggle one prot flag in a future proof way,
>> so i don't think this solves the issue completely.
>
> Ack -- I illustrated this model because it makes the seccomp filter's
> job easy, but it does have limitations.
>
>> i think we might need a new api, given that aarch64
>> now has PROT_BTI and PROT_MTE while existing code
>> expects RWX only, but i don't know what api is best.
>
> An alternative option would be a call that sets / clears chosen
> flags and leaves others unchanged.
I tend to favor a set/clear API, but that could also just be done by
creating a new PROT_BTI_IF_X which enables BTI for areas already set to
_EXEC. That goes right by the seccomp filters too, and actually is
closer to what glibc wants to do anyway.
>
> The trouble with that is that the MDWX policy then becomes hard to
> implement again.
>
>
> But policies might be best set via another route, such as a prctl,
> rather than being implemented completely in a seccomp filter.
>
> Cheers
> ---Dave
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-10-26 22:41 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <8584c14f-5c28-9d70-c054-7c78127d84ea@arm.com>
2020-10-22 7:18 ` [systemd-devel] BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures Lennart Poettering
2020-10-22 7:54 ` Florian Weimer
2020-10-22 8:17 ` Topi Miettinen
2020-10-22 8:25 ` Florian Weimer
2020-10-22 8:29 ` Szabolcs Nagy
2020-10-22 8:38 ` Lennart Poettering
2020-10-22 9:31 ` Catalin Marinas
2020-10-22 10:12 ` Topi Miettinen
2020-10-22 10:27 ` Florian Weimer
2020-10-23 6:13 ` Szabolcs Nagy
2020-10-23 9:04 ` Catalin Marinas
2020-10-22 10:03 ` Topi Miettinen
2020-10-22 8:05 ` Szabolcs Nagy
2020-10-22 8:31 ` Lennart Poettering
[not found] ` <20201022075447.GO3819@arm.com>
2020-10-22 10:39 ` Topi Miettinen
2020-10-22 20:02 ` Kees Cook
2020-10-22 22:24 ` Topi Miettinen
2020-10-23 17:52 ` Salvatore Mesoraca
2020-10-24 11:34 ` Topi Miettinen
2020-10-24 14:12 ` Salvatore Mesoraca
2020-10-25 13:42 ` Jordan Glover
2020-10-23 9:02 ` Catalin Marinas
2020-10-24 11:01 ` Topi Miettinen
2020-10-26 14:52 ` Catalin Marinas
2020-10-26 15:56 ` Dave Martin
2020-10-26 16:51 ` Mark Brown
2020-10-26 16:31 ` Topi Miettinen
2020-10-26 16:24 ` Dave Martin
2020-10-26 16:39 ` Topi Miettinen
2020-10-26 16:45 ` Florian Weimer
2020-10-27 14:22 ` Dave Martin
2020-10-27 14:41 ` Florian Weimer
2020-10-26 16:57 ` Szabolcs Nagy
2020-10-26 17:52 ` Dave Martin
2020-10-26 22:39 ` Jeremy Linton [this message]
2020-10-27 14:15 ` Dave Martin
2020-10-29 11:02 ` Catalin Marinas
2020-11-04 12:18 ` Dave Martin
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=45c64b49-a38b-4b0c-d9cf-6c586dacbcc9@arm.com \
--to=jeremy.linton@arm.com \
--cc=Catalin.Marinas@arm.com \
--cc=Dave.Martin@arm.com \
--cc=broonie@kernel.org \
--cc=keescook@chromium.org \
--cc=libc-alpha@sourceware.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=systemd-devel@lists.freedesktop.org \
--cc=szabolcs.nagy@arm.com \
--cc=toiwoton@gmail.com \
--cc=will.deacon@arm.com \
/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).