linux-kernel - Re: [PATCH bpf] selftests/bpf: DENYLIST.aarch64: Remove fexit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQKXEM5LaGktduyG=EH+2udkH-ZJpo4u57BUchregJy8NQ@mail.gmail.com>
Date: Mon, 15 Jul 2024 10:07:20 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>, Manu Bretelle <chantra@...a.com>, 
	KP Singh <kpsingh@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Mykola Lysenko <mykolal@...a.com>, 
	Alexei Starovoitov <ast@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Shuah Khan <shuah@...nel.org>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, 
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Florent Revest <revest@...gle.com>
Subject: Re: [PATCH bpf] selftests/bpf: DENYLIST.aarch64: Remove fexit_sleep

On Mon, Jul 15, 2024 at 9:32 AM Puranjay Mohan <puranjay@...nel.org> wrote:
>
>
> Hi Daniel, Manu
> I was able to reproduce this issue on KVM and found the root cause for
> this hang! The other issue that we fixed is unrelated to this hang and
> doesn't occur on self hosted github runners as they use 48-bit VAs.
>
> The userspace test code has:
>
>     #define STACK_SIZE (1024 * 1024)
>     static char child_stack[STACK_SIZE];
>
>     cpid = clone(do_sleep, child_stack + STACK_SIZE, CLONE_FILES | SIGCHLD, fexit_skel);
>
> arm64 requires the stack pointer to be 16 byte aligned otherwise
> SPAlignmentFault occurs, this appears as Bus error in the userspace.
>
> The stack provided to the clone system call is not guaranteed to be
> aligned properly in this selftest.
>
> The test hangs on the following line:
>     while (READ_ONCE(fexit_skel->bss->fentry_cnt) != 2);
>
> Because the child process is killed due to SPAlignmentFault, the
> fentry_cnt remains at 0!
>
> Reading the man page of clone system call, the correct way to allocate
> stack for this call is using mmap like this:
>
> stack = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
>
> This fixes the issue, I will send a patch to use this and once again
> remove this test from DENYLIST and I hope this time it fixes it for good.

Wow. Great find. Good to know.
prog_tests/ns_current_pid_tgid.c has the same issue probably.