linux-kernel - Re: [PATCH 1/2] x86: Fix kernel panic when booting with XD disabled in uEFI firmware

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Message-ID: <20151204164057.GE2514@codeblueprint.co.uk>
Date:	Fri, 4 Dec 2015 16:40:57 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Kosuke Tatsukawa <tatsu@...jp.nec.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 1/2] x86: Fix kernel panic when booting with XD disabled
 in uEFI firmware

On Thu, 03 Dec, at 11:58:33PM, Kosuke Tatsukawa wrote:
> The kernel panics early in boot on a x86_64 server if the eXecute
> Disable (XD) bit is set to disabled in the uEFI firmware.  The message
> in the kernel log buffer looks like below.
> ------------------------------------------------------------------------
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc3 #1
> [    0.000000]  0000000000000000 261c6fa13723be1b ffffffff819b7e40 ffffffff8131f320
> [    0.000000]  ffffffffffffffff ffffffff819b7f30 ffffffff81b261b0 000000000000001c
> [    0.000000]  ffffffff81d77a1c 0000000000000010 00000000be35a000 ffffffffff200000
> [    0.000000] Call Trace:
> [    0.000000]  [<ffffffff8131f320>] dump_stack+0x44/0x64
> [    0.000000]  [<ffffffff81b261b0>] early_idt_handler_common+0x90/0xd0
> [    0.000000]  [<ffffffff81b2f1c5>] ? setup_arch+0x1f1/0xce0
> [    0.000000]  [<ffffffff81b2f1c5>] ? setup_arch+0x1f1/0xce0
> [    0.000000]  [<ffffffff81b26120>] ? early_idt_handler_array+0x120/0x120
> [    0.000000]  [<ffffffff81b26d81>] start_kernel+0xe6/0x4f0
> [    0.000000]  [<ffffffff81b26120>] ? early_idt_handler_array+0x120/0x120
> [    0.000000]  [<ffffffff81b26120>] ? early_idt_handler_array+0x120/0x120
> [    0.000000]  [<ffffffff81b265ee>] x86_64_start_reservations+0x2a/0x2c
> [    0.000000]  [<ffffffff81b2673c>] x86_64_start_kernel+0x14c/0x16f
> [    0.000000] RIP 0x80000000be359163
> ------------------------------------------------------------------------
> 
> The panic occurs because __early_set_fixmap() called from
> parse_setup_data() unconditionally sets the PTE with FIXMAP_PAGE_NORMAL,
> which contains _PAGE_NX and causes an exception.
> 
> This patch modifies __early_set_fixmap() to set _PAGE_NX only when the
> hardware supports it.  It also moves the call to x86_configure_nx()
> earlier in setup_arch() before __early_set_fixmap() is first called.
> 
> The above problem occurs after __early_set_fixmap() is called from
> parse_setup_data().  However, since setup_olpc_ofw_pgd() can also call
> __early_set_fixmap(), the patch moves the call to x86_configure_nx()
> before that.
> 
> Signed-off-by: Kosuke Tatsukawa <tatsu@...jp.nec.com>
> ---
>  arch/x86/kernel/setup.c |   18 +++++++++---------
>  arch/x86/mm/ioremap.c   |    3 +++
>  2 files changed, 12 insertions(+), 9 deletions(-)

Could you try booting with the commit 04633df0c43d ("x86/cpu: Call
verify_cpu() after having entered long mode too") instead? It's part
of v4.4-rc1.

Allowing NX to be disabled should be avoided.
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