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From: Puranjay Mohan <puranjay12@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>, David Ahern
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Subject: Re: [PATCH bpf v5] bpf: verifier: prevent userspace memory access
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References: <20240324185356.59111-1-puranjay12@gmail.com>
 <CAADnVQKW2ajQ25BkOO_D2=N2wOHt9fdNY+tWRunXe_sN-w+33g@mail.gmail.com>
Date: Sun, 24 Mar 2024 19:34:56 +0000
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Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Sun, Mar 24, 2024 at 11:54=E2=80=AFAM Puranjay Mohan <puranjay12@gmail=
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?

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