From: Alexey Izbyshev <izbyshev@ispras.ru>
To: Florent Revest <revest@chromium.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, catalin.marinas@arm.com,
anshuman.khandual@arm.com, joey.gouly@arm.com, mhocko@suse.com,
keescook@chromium.org, david@redhat.com, peterx@redhat.com,
nd@arm.com, broonie@kernel.org, szabolcs.nagy@arm.com
Subject: Re: [PATCH 4/4] kselftest: vm: Add tests for no-inherit memory-deny-write-execute
Date: Sat, 06 May 2023 00:26:10 +0300 [thread overview]
Message-ID: <3a38319a3b241e578729ffa5484ad24b@ispras.ru> (raw)
In-Reply-To: <CABRcYmKXrPE0oP9R=qsn=mL3Nwm_mVqT-r-TvOvowTdiuYU--A@mail.gmail.com>
On 2023-05-05 19:42, Florent Revest wrote:
> On Thu, May 4, 2023 at 10:30 PM Alexey Izbyshev <izbyshev@ispras.ru>
> wrote:
>>
>> On 2023-05-04 20:09, Florent Revest wrote:
>> > Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
>> > PR_SET_MDWE prctl.
>> >
>> > Signed-off-by: Florent Revest <revest@chromium.org>
>> > ---
>> > tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
>> > 1 file changed, 89 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/tools/testing/selftests/mm/mdwe_test.c
>> > b/tools/testing/selftests/mm/mdwe_test.c
>> > index 91aa9c3099e7..9f08ed1b99ae 100644
>> > --- a/tools/testing/selftests/mm/mdwe_test.c
>> > +++ b/tools/testing/selftests/mm/mdwe_test.c
>> > @@ -22,6 +22,8 @@
>> >
>> > TEST(prctl_flags)
>> > {
>> > + EXPECT_LT(prctl(PR_SET_MDWE, PR_MDWE_NO_INHERIT, 0L, 0L, 7L), 0);
>> > +
>>
>> PR_MDWE_NO_INHERIT is defined to an int constant, so passing it to
>> prctl() without a cast to long or similar may produce wrong code on
>> 64-bit targets (ABIs typically don't require the compiler to clear the
>> upper 32 bits of a 64-bit register when passing a 32-bit argument, so
>> va_arg(arg, unsigned long) in prctl() implementation might get junk).
>
> Ah, good catch Alexey! :)
>
>> Arguably, defining PR_MDWE_* to plain int constants is a bug, or at
>> least a footgun for users of uapi headers.
>
> As part of the next version of this series, I'm happy to:
> 1- change the existing PR_MDWE_REFUSE_EXEC_GAIN to 1UL
> 2- introduce PR_MDWE_NO_INHERIT as 2UL
>
Yes, I think it's the right thing to do. I suggest to spell them as (1UL
<< 0), etc. for consistency with all other unsigned long flags in the
header.
> But I'm surprised that most of the macros in
> include/uapi/linux/prctl.h are the same sort of footguns already ?
> Hasn't it been an issue for other prctls yet ?
Yes, they are. I'm not aware of a public discussion of this specific
issue, but note that at least for some prctl() options the kernel
doesn't care about upper bits because arguments are truncated before
doing anything else with them (e.g. for PR_SCHED_CORE raw prctl()
arguments are implicitly converted to what sched_core_share_pid()
expects). Also, actually getting junk in the upper bits might not always
be easy (e.g. on x86-64 all or almost all instructions with r32
destination operand clear the upper bits). Unfortunately, I don't have a
better answer than this.
Alexey
next prev parent reply other threads:[~2023-05-05 21:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-04 17:09 [PATCH 0/4] MDWE without inheritance Florent Revest
2023-05-04 17:09 ` [PATCH 1/4] kselftest: vm: Fix tabs/spaces inconsistency in the mdwe test Florent Revest
2023-05-04 17:09 ` [PATCH 2/4] kselftest: vm: Fix mdwe's mmap_FIXED test case Florent Revest
2023-05-04 17:13 ` Florent Revest
2023-05-04 17:09 ` [PATCH 3/4] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Florent Revest
2023-05-05 18:34 ` Catalin Marinas
2023-05-08 12:11 ` Florent Revest
2023-05-04 17:09 ` [PATCH 4/4] kselftest: vm: Add tests for no-inherit memory-deny-write-execute Florent Revest
2023-05-04 20:29 ` Alexey Izbyshev
2023-05-05 16:42 ` Florent Revest
2023-05-05 21:26 ` Alexey Izbyshev [this message]
2023-05-08 12:12 ` Florent Revest
2023-05-04 20:06 ` [PATCH 0/4] MDWE without inheritance Peter Xu
2023-05-05 16:42 ` Florent Revest
2023-05-08 1:29 ` Peter Xu
2023-05-08 12:12 ` Florent Revest
2023-05-08 14:10 ` Catalin Marinas
2023-05-08 17:21 ` Topi Miettinen
2023-05-09 10:04 ` Catalin Marinas
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=3a38319a3b241e578729ffa5484ad24b@ispras.ru \
--to=izbyshev@ispras.ru \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=david@redhat.com \
--cc=joey.gouly@arm.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=nd@arm.com \
--cc=peterx@redhat.com \
--cc=revest@chromium.org \
--cc=szabolcs.nagy@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).