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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Sun, 24 Mar 2024 13:47:58 -0700
Message-ID: <CAADnVQJdoC6JaVu+m2bfC3QHkTSpbA9LyiMyAnjhght_-_EP5Q@mail.gmail.com>
Subject: Re: [PATCH bpf v5] bpf: verifier: prevent userspace memory access
To: Puranjay Mohan <puranjay12@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>, David Ahern <dsahern@kernel.org>, 
	Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, 
	Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, 
	Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, John Fastabend <john.fastabend@gmail.com>, 
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
	Jiri Olsa <jolsa@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, X86 ML <x86@kernel.org>, 
	"H. Peter Anvin" <hpa@zytor.com>, Jean-Philippe Brucker <jean-philippe@linaro.org>, 
	Network Development <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>, 
	LKML <linux-kernel@vger.kernel.org>, Ilya Leoshkevich <iii@linux.ibm.com>
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On Sun, Mar 24, 2024 at 12:35=E2=80=AFPM Puranjay Mohan <puranjay12@gmail.c=
om> wrote:
>
> Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
>
> > On Sun, Mar 24, 2024 at 11:54=E2=80=AFAM Puranjay Mohan <puranjay12@gma=
il.com> wrote:
> >>
> >> +u64 bpf_arch_uaddress_limit(void)
> >> +{
> >> +       return max(TASK_SIZE_MAX + PAGE_SIZE, VSYSCALL_ADDR);
> >
> > This is broken. See my other email.
> > Sadly you didn't test it.
>
> Yes, sorry for this. I was relying on the CI for the test this time as
> thought it would work. I just realised this would reject all addresses!
>
> Given that the current x86-64 JIT just tests for TASK_SIZE_MAX +
> PAGE_SIZE can we go ahead with this and later fix it for VSYSCALL_ADDR
> as it is specific for x86-64?

This patch deletes a bunch of code from arch/x86/net/bpf_jit_comp.c.
If you're proposing to deal with vsyscall check in JIT then
very similar code in the same spot will be re-introduced.
So we should address all issues at once to avoid code churn.

> Also, I will spend some time figuring out the best way to do this, there
> should be some mathematical trick somewhere.

Let's think of it right now.

For the next patch you can reduce the cc list to avoid spamming all
mailing lists.
bpf@vger plus JIT folks for affected arches will be enough.