linux-kernel - Re: [PATCH 4.14 v2 1/4] bpf: Do not use ax register in interpreter on div/mod

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Message-ID: <Y/crdG+quVvKMF0m@kroah.com>
Date:   Thu, 23 Feb 2023 10:01:40 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Edward Liaw <edliaw@...gle.com>
Cc:     stable@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>, bpf@...r.kernel.org,
        kernel-team@...roid.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: Re: [PATCH 4.14 v2 1/4] bpf: Do not use ax register in interpreter
 on div/mod

On Wed, Feb 22, 2023 at 07:29:21PM +0000, Edward Liaw wrote:
> From: Daniel Borkmann <daniel@...earbox.net>
> 
> Partially undo old commit 144cd91c4c2b ("bpf: move tmp variable into ax
> register in interpreter"). The reason we need this here is because ax
> register will be used for holding temporary state for div/mod instruction
> which otherwise interpreter would corrupt. This will cause a small +8 byte
> stack increase for interpreter, but with the gain that we can use it from
> verifier rewrites as scratch register.
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Reviewed-by: John Fastabend <john.fastabend@...il.com>
> [cascardo: This partial revert is needed in order to support using AX for
> the following two commits, as there is no JMP32 on 4.19.y]
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
> [edliaw: Removed redeclaration of tmp]
> Signed-off-by: Edward Liaw <edliaw@...gle.com>
> ---
>  kernel/bpf/core.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)

What is the git commit id in Linus's tree of this commit?

thanks,

greg k-h