netdev - Re: [PATCH bpf v5] bpf: verifier: prevent userspace memory access

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Date: Sun, 24 Mar 2024 13:47:58 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Puranjay Mohan <puranjay12@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, 
	"H. Peter Anvin" <hpa@...or.com>, Jean-Philippe Brucker <jean-philippe@...aro.org>, 
	Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: Re: [PATCH bpf v5] bpf: verifier: prevent userspace memory access

On Sun, Mar 24, 2024 at 12:35 PM Puranjay Mohan <puranjay12@...il.com> wrote:
>
> Alexei Starovoitov <alexei.starovoitov@...il.com> writes:
>
> > On Sun, Mar 24, 2024 at 11:54 AM Puranjay Mohan <puranjay12@...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@...r plus JIT folks for affected arches will be enough.