Matt Fleming wrote:
> 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@xxxxxxxxxxxxx>
>> ---
>> 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.
Thank you pointing that out.
linux-4.4-rc3 booted without a problem on a real server even with XD
turned off by the firmware. I didn't notice this before because I was
using an older version of the kernel on the real server, and doing
investigation on a KVM guest.
The "noexec=off" kernel parameter still seems to come up with EFI
runtime service disabled though. Do you think this should be left alone
as an disadvantage for using a bad option?
---
Kosuke TATSUKAWA | 3rd IT Platform Department
| IT Platform Division, NEC Corporation
| tatsu@xxxxxxxxxxxxx
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