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Date:   Mon, 24 Oct 2022 19:41:27 +0200
From:   Pavel Machek <pavel@denx.de>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, xen-devel@lists.xenproject.org,
        Kees Cook <keescook@chromium.org>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 4.19 174/229] x86/entry: Work around Clang __bdos() bug
Message-ID: <20221024174127.GC25198@duo.ucw.cz>
References: <20221024112959.085534368@linuxfoundation.org>
 <20221024113004.718917343@linuxfoundation.org>
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Hi!

> From: Kees Cook <keescook@chromium.org>
>=20
> [ Upstream commit 3e1730842f142add55dc658929221521a9ea62b6 ]
>=20
> Clang produces a false positive when building with CONFIG_FORTIFY_SOURCE=
=3Dy
> and CONFIG_UBSAN_BOUNDS=3Dy when operating on an array with a dynamic
> offset. Work around this by using a direct assignment of an empty
> instance. Avoids this warning:
>=20
> ../include/linux/fortify-string.h:309:4: warning: call to __write_overflo=
w_field declared with 'warn
> ing' attribute: detected write beyond size of field (1st parameter); mayb=
e use struct_group()? [-Wat
> tribute-warning]
>                         __write_overflow_field(p_size_field, size);
>                         ^
>=20
> which was isolated to the memset() call in xen_load_idt().
>=20
> Note that this looks very much like another bug that was worked around:
> https://github.com/ClangBuiltLinux/linux/issues/1592

We don't have CONFIG_UBSAN_BOUNDS in 4.19, so maybe we don't need this
one?

Best regards,
								Pavel
							=09
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -752,6 +752,7 @@ static void xen_load_idt(const struct desc_ptr *desc)
>  {
>  	static DEFINE_SPINLOCK(lock);
>  	static struct trap_info traps[257];
> +	static const struct trap_info zero =3D { };
>  	unsigned out;
> =20
>  	trace_xen_cpu_load_idt(desc);
> @@ -761,7 +762,7 @@ static void xen_load_idt(const struct desc_ptr *desc)
>  	memcpy(this_cpu_ptr(&idt_desc), desc, sizeof(idt_desc));
> =20
>  	out =3D xen_convert_trap_info(desc, traps, false);
> -	memset(&traps[out], 0, sizeof(traps[0]));
> +	traps[out] =3D zero;
> =20
>  	xen_mc_flush();
>  	if (HYPERVISOR_set_trap_table(traps))
> --=20
> 2.35.1
>=20
>=20

--=20
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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