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Message-ID: <1516351586.5087.9.camel@amazon.co.uk>
Subject: Re: [PATCH] x86/mce: Make machine check speculation protected
To:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
CC:     <x86@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, <stable@vger.kernel.org>,
        "Ghitulete, Razvan-alin" <rga@amazon.com>
In-Reply-To: <alpine.DEB.2.20.1801181626290.1847@nanos>
References: <alpine.DEB.2.20.1801181626290.1847@nanos>
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Organization: Amazon
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Date:   Fri, 19 Jan 2018 09:46:26 +0100
MIME-Version: 1.0
From:   "Woodhouse, David" <dwmw@amazon.co.uk>
Sender: linux-kernel-owner@vger.kernel.org
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On Thu, 2018-01-18 at 16:28 +0100, Thomas Gleixner wrote:
> The machine check idtentry uses an indirect branch directly from the low
> level code. This evades the speculation protection.
>=20
> Replace it by a direct call into C code and issue the indirect call there
> so the compiler can apply the proper speculation protection.
>=20
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Cc: stable for at least 4.9.

> ---
> =C2=A0arch/x86/entry/entry_64.S=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0|=C2=A0=C2=A0=C2=A0=C2=A02 +-
> =C2=A0arch/x86/include/asm/traps.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0|=C2=A0=
=C2=A0=C2=A0=C2=A01 +
> =C2=A0arch/x86/kernel/cpu/mcheck/mce.c |=C2=A0=C2=A0=C2=A0=C2=A05 +++++
> =C2=A03 files changed, 7 insertions(+), 1 deletion(-)
>=20
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1264,7 +1264,7 @@ idtentry async_page_fault	do_async_page_
> =C2=A0#endif
> =C2=A0
> =C2=A0#ifdef CONFIG_X86_MCE
> -idtentry machine_check					has_error_code=3D0	paranoid=3D1 do_sym=3D*mac=
hine_check_vector(%rip)
> +idtentry machine_check		do_mce			has_error_code=3D0	paranoid=3D1
> =C2=A0#endif
> =C2=A0
> =C2=A0/*
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -88,6 +88,7 @@ dotraplinkage void do_simd_coprocessor_e
> =C2=A0#ifdef CONFIG_X86_32
> =C2=A0dotraplinkage void do_iret_error(struct pt_regs *, long);
> =C2=A0#endif
> +dotraplinkage void do_mce(struct pt_regs *, long);
> =C2=A0
> =C2=A0static inline int get_si_code(unsigned long condition)
> =C2=A0{
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -1785,6 +1785,11 @@ static void unexpected_machine_check(str
> =C2=A0void (*machine_check_vector)(struct pt_regs *, long error_code) =3D
> =C2=A0						unexpected_machine_check;
> =C2=A0
> +dotraplinkage void do_mce(struct pt_regs *regs, long error_code)
> +{
> +	machine_check_vector(regs, error_code);
> +}
> +
> =C2=A0/*
> =C2=A0 * Called for each booted CPU to set up machine checks.
> =C2=A0 * Must be called with preempt off:
>=20
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