linux-kernel - Re: [PATCH bpf] bpf: verifier: prevent userspace memory access

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Message-ID: <CAADnVQJ3o6DsURi=N_KXx+mbW9r7__3LrwYLyYwuoMOsqFHPkw@mail.gmail.com>
Date: Wed, 20 Mar 2024 23:08:00 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Puranjay Mohan <puranjay12@...il.com>, Ilya Leoshkevich <iii@...ux.ibm.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>
Subject: Re: [PATCH bpf] bpf: verifier: prevent userspace memory access

On Wed, Mar 20, 2024 at 3:55 AM Puranjay Mohan <puranjay12@...il.com> wrote:
>
> The JITs need to implement bpf_arch_uaddress_limit() to define where
> the userspace addresses end for that architecture or TASK_SIZE is taken
> as default.
>
> The implementation is as follows:
>
> REG_AX =  SRC_REG
> if(offset)
>         REG_AX += offset;
> REG_AX >>= 32;
> if (REG_AX <= (uaddress_limit >> 32))
>         DST_REG = 0;
> else
>         DST_REG = *(size *)(SRC_REG + offset);

The patch looks good, but it seems to be causing s390 CI failures.

Ilya,
could you help us understand is this check needed on s390
and if so, what should be the uaddress_limit ?