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Mon, 30 Dec 2024 08:16:19 -0800 (PST) Received: from krava ([213.175.46.84]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-aac0e830ae6sm1486108366b.22.2024.12.30.08.16.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Dec 2024 08:16:19 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 30 Dec 2024 17:16:17 +0100 To: Daniel Xu , Andrei Enache Cc: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next] libbpf: Set MFD_NOEXEC_SEAL when creating memfd Message-ID: References: <6bf30e1a22d867af9145aa5e94c3fd9281a1c98d.1735508627.git.dxu@dxuuu.xyz> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6bf30e1a22d867af9145aa5e94c3fd9281a1c98d.1735508627.git.dxu@dxuuu.xyz> On Sun, Dec 29, 2024 at 02:44:33PM -0700, Daniel Xu wrote: > Since 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC"), the > kernel has started printing a warning if neither MFD_NOEXEC_SEAL nor > MFD_EXEC is set in memfd_create(). > > To avoid this warning (and also be more secure), set MFD_NOEXEC_SEAL by > default. But since libbpf can be running on potentially very old > kernels, leave a fallback for kernels without MFD_NOEXEC_SEAL support. > > Signed-off-by: Daniel Xu there's similar change posted by Andrei already: https://lore.kernel.org/bpf/eTid-pMaxx4d_gMkyFN6fgVGub01RRJYIl1SzTmRG7RtRlPUJOMrVfe2I1W8s0OBHBFy3UN2WGm_e6mak0nGcrZ4ZdxAYRUSDDcUSVMvNA4=@proton.me/T/#u jirka > --- > tools/lib/bpf/libbpf.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 66173ddb5a2d..46492cc0927d 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -1731,12 +1731,24 @@ static int sys_memfd_create(const char *name, unsigned flags) > #ifndef MFD_CLOEXEC > #define MFD_CLOEXEC 0x0001U > #endif > +#ifndef MFD_NOEXEC_SEAL > +#define MFD_NOEXEC_SEAL 0x0008U > +#endif > > static int create_placeholder_fd(void) > { > + unsigned int flags = MFD_CLOEXEC | MFD_NOEXEC_SEAL; > + const char *name = "libbpf-placeholder-fd"; > int fd; > > - fd = ensure_good_fd(sys_memfd_create("libbpf-placeholder-fd", MFD_CLOEXEC)); > + fd = ensure_good_fd(sys_memfd_create(name, flags)); > + if (fd >= 0) > + return fd; > + else if (errno != EINVAL) > + return -errno; > + > + /* Possibly running on kernel without MFD_NOEXEC_SEAL */ > + fd = ensure_good_fd(sys_memfd_create(name, flags & ~MFD_NOEXEC_SEAL)); > if (fd < 0) > return -errno; > return fd; > -- > 2.47.1 >