linux-kernel - Re: [PATCH] arm64/bpf: use movn/movk/movk sequence to generate kernel addresses

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Message-ID: <c8f11ce3-1ab4-5e54-85f6-2431c7eb8a7a@iogearbox.net>
Date:   Tue, 27 Nov 2018 19:24:40 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, ast@...com
Subject: Re: [PATCH] arm64/bpf: use movn/movk/movk sequence to generate kernel
 addresses

On 11/27/2018 07:22 PM, Will Deacon wrote:
> Hi Ard,
> 
> On Fri, Nov 23, 2018 at 06:29:02PM +0100, Ard Biesheuvel wrote:
>> On arm64, all executable code is guaranteed to reside in the vmalloc
>> space (or the module space), and so jump targets will only use 48
>> bits at most, and the remaining bits are guaranteed to be 0x1.
>>
>> This means we can generate an immediate jump address using a sequence
>> of one MOVN (move wide negated) and two MOVK instructions, where the
>> first one sets the lower 16 bits but also sets all top bits to 0x1.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
> 
> Acked-by: Will Deacon <will.deacon@....com>
> 
> Denial, Alexei, shall I take this via arm64, or would you rather take
> it via davem?

Yeah we can take it via bpf trees, thanks.

Cheers,
Daniel