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Subject: Re: [PATCH 14/21] x86/xen: Support objtool vmlinux.o validation in
 xen-head.S
To:     Josh Poimboeuf <jpoimboe@redhat.com>, x86@kernel.org
Cc:     linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux@googlegroups.com,
        Miroslav Benes <mbenes@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
References: <cover.1610652862.git.jpoimboe@redhat.com>
 <02a3b646aa20035c9c700c5b6d7897a9f898ba24.1610652862.git.jpoimboe@redhat.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <43d47af1-6735-6651-db11-4489c86c62a2@suse.com>
Date:   Fri, 15 Jan 2021 06:17:25 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>, x86@kernel.org
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
 Sami Tolvanen <samitolvanen@google.com>, Sedat Dilek
 <sedat.dilek@gmail.com>, Kees Cook <keescook@chromium.org>,
 Nick Desaulniers <ndesaulniers@google.com>,
 clang-built-linux@googlegroups.com, Miroslav Benes <mbenes@suse.cz>,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <43d47af1-6735-6651-db11-4489c86c62a2@suse.com>
Subject: Re: [PATCH 14/21] x86/xen: Support objtool vmlinux.o validation in
 xen-head.S
References: <cover.1610652862.git.jpoimboe@redhat.com>
 <02a3b646aa20035c9c700c5b6d7897a9f898ba24.1610652862.git.jpoimboe@redhat.com>
In-Reply-To: <02a3b646aa20035c9c700c5b6d7897a9f898ba24.1610652862.git.jpoimboe@redhat.com>

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On 14.01.21 20:40, Josh Poimboeuf wrote:
> The Xen hypercall page is filled with zeros, causing objtool to fall
> through all the empty hypercall functions until it reaches a real
> function, resulting in a stack state mismatch.
>=20
> The build-time contents of the hypercall page don't matter, since it
> gets mapped to the hypervisor.

This sentence is technically wrong: the contents don't matter, as the
page will be rewritten by the hypervisor.


Juergen


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