linux-kernel - Re: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR

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Message-ID: <CAJhGHyAYQv5YzyvQdpBO3yZ5g-omqYA9cCXu-SKp+3kT=U32pw@mail.gmail.com>
Date:   Sat, 7 May 2022 10:54:18 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Mark Rutland <mark.rutland@....com>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat

On Fri, May 6, 2022 at 8:20 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Since the upper regs don't exist for ia32 code, preserving them
> doesn't hurt and it simplifies the code.
>
> This doesn't add any attack surface that would not already be
> available through INT80.
>
> Notably:
>
>  - 32bit SYSENTER: didn't clear si, dx, cx.
>
>  - 32bit SYSCALL, INT80: *do* clear si since the C functions don't
>    take a second argument.
>
>  - 64bit: didn't clear si since the C functions take a second
>    argument; except the error_entry path might have only one argument,
>    so clearing si was missing here.
>
> 32b SYSENTER should be clearing all those 3 registers, nothing uses them
> and selftests pass.
>
> Unconditionally clear rsi since it simplifies code.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Borislav Petkov <bp@...e.de>


Reviewed-by: Lai Jiangshan <jiangshanlai@...il.com>