[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <mb61pwmpvst3v.fsf@gmail.com>
Date: Thu, 21 Mar 2024 11:48:52 +0000
From: Puranjay Mohan <puranjay12@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...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 v2] bpf: verifier: prevent userspace memory access
Alexei Starovoitov <alexei.starovoitov@...il.com> writes:
> On Thu, Mar 21, 2024 at 4:05 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
>>
>> On Thu, Mar 21, 2024 at 3:11 AM Puranjay Mohan <puranjay12@...il.com> wrote:
>> >
>> > diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
>> > index e613eebfd349..e61a51a5b4be 100644
>> > --- a/arch/s390/net/bpf_jit_comp.c
>> > +++ b/arch/s390/net/bpf_jit_comp.c
>> > @@ -2691,3 +2691,8 @@ bool bpf_jit_supports_subprog_tailcalls(void)
>> > {
>> > return true;
>> > }
>> > +
>> > +u64 bpf_arch_uaddress_limit(void)
>> > +{
>> > + return -ENOTSUPP;
>> > +}
>>
>> Looks good and should work, but s390 CI is still not happy.
>> Ideas?
>> sock tests were not failing before. So something is going on.
>
> I think I have an explanation.
> -ENOTSUPP and u64... and later:
> u64 uaddress_limit = bpf_arch_uaddress_limit()
> if (uaddress_limit < 0)
>
> I bet the compiler simply removes this check since unsigned cannot
> be negative.
> Odd that there is no compiler warning.
>
> pw-bot: cr
>
Yes, I verified that the compiler is removing this:
if (BPF_CLASS(insn->code) == BPF_LDX &&
a944: 7100047f cmp w3, #0x1
a948: 540013e1 b.ne abc4 <do_misc_fixups+0x66c> // b.any
a94c: 721a041f tst w0, #0xc0
a950: 54fff4e1 b.ne a7ec <do_misc_fixups+0x294> // b.any
u64 uaddress_limit = bpf_arch_uaddress_limit();
a954: b90003e6 str w6, [sp]
a958: 94000000 bl 0 <bpf_arch_uaddress_limit>
*patch++ = BPF_MOV64_REG(BPF_REG_AX, insn->src_reg);
We should do:
if (!uaddress_limit)
goto next_insn;
and in the disabled case return 0 in place of -ENOSUPP.
Doing this adds the check:
if (BPF_CLASS(insn->code) == BPF_LDX &&
a944: 7100047f cmp w3, #0x1
a948: 54001401 b.ne abc8 <do_misc_fixups+0x670> // b.any
a94c: 721a041f tst w0, #0xc0
a950: 54fff4e1 b.ne a7ec <do_misc_fixups+0x294> // b.any
u64 uaddress_limit = bpf_arch_uaddress_limit();
a954: b90003e6 str w6, [sp]
a958: 94000000 bl 0 <bpf_arch_uaddress_limit>
if (!uaddress_limit)
a95c: b4fff020 cbz x0, a760 <do_misc_fixups+0x208>
*patch++ = BPF_MOV64_REG(BPF_REG_AX, insn->src_reg);
I will send v3 with this approach.
Thanks,
Puranjay
Powered by blists - more mailing lists