linux-kernel - Re: [PATCH 3/6] x86/entry/64/compat: Fix Xen PV SYSENTER frame setup

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Date:   Sat, 27 Jun 2020 22:47:20 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 3/6] x86/entry/64/compat: Fix Xen PV SYSENTER frame setup

On 6/26/20 1:21 PM, Andy Lutomirski wrote:
> The SYSENTER frame setup was nonsense.  It worked by accident
> because the normal code into which the Xen asm jumped
> (entry_SYSENTER_32/compat) threw away SP without touching the stack.
> entry_SYSENTER_compat was recently modified such that it relied on
> having a valid stack pointer, so now the Xen asm needs to invoke it
> with a valid stack.
>
> Fix it up like SYSCALL: use the Xen-provided frame and skip the bare
> metal prologue.
>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Stefano Stabellini <sstabellini@...nel.org>
> Cc: xen-devel@...ts.xenproject.org
> Fixes: 1c3e5d3f60e2 ("x86/entry: Make entry_64_compat.S objtool clean")
> Signed-off-by: Andy Lutomirski <luto@...nel.org>


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>