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Re: [Xen-devel] [PATCH] x86: Fix boot with CONFIG_XSM enabled following c/s 7177f589ba
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 7 Jun 2019 13:20:04 +0100
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 07 Jun 2019 12:20:14 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 07/06/2019 13:12, Andrew Cooper wrote:
> On 07/06/2019 13:07, Andrew Cooper wrote:
>> Currently, booting staging fails with:
>>
>> (XEN) Using APIC driver default
>> (XEN) ----[ Xen-4.13-unstable x86_64 debug=y Not tainted ]----
>> (XEN) CPU: 0
>> (XEN) RIP: e008:[<ffff82d08038f66e>] __x86_indirect_thunk_rax+0xe/0x10
>> (XEN) RFLAGS: 0000000000010016 CONTEXT: hypervisor
>> (XEN) rax: c2c2c2c2c2c2c2c2 rbx: ffff83003f4cc000 rcx: 0000000000000000
>> <snip>
>> (XEN) Xen code around <ffff82d08038f66e>
>> (__x86_indirect_thunk_rax+0xe/0x10):
>> (XEN) ae e8 eb fb 48 89 04 24 <c3> 90 e8 05 00 00 00 0f ae e8 eb fb 48 89
>> 0c 24
>> (XEN) Xen stack trace from rsp=ffff82d080827d28:
>> (XEN) c2c2c2c2c2c2c2c2 ffff82d080207588 ffff82d080827d68
>> 0000000000000000
>> <snip>
>> (XEN) Xen call trace:
>> (XEN) [<ffff82d08038f66e>] __x86_indirect_thunk_rax+0xe/0x10
>> (XEN) [<ffff82d0806078a9>] setup_system_domains+0x18/0xab
>> (XEN) [<ffff82d08062d9c8>] __start_xen+0x1ea9/0x2935
>> (XEN) [<ffff82d0802000f3>] __high_start+0x53/0x55
>> (XEN)
>> (XEN) ****************************************
>> (XEN) Panic on CPU 0:
>> (XEN) GENERAL PROTECTION FAULT
>> (XEN) [error_code=0000]
>> (XEN) ****************************************
>>
>> UBSAN (which I happened to have active in my build at the time) identifies
>> the
>> problem explicitly:
>>
>> (XEN) Using APIC driver default
>> (XEN)
>> ================================================================================
>> (XEN) UBSAN: Undefined behaviour in
>> /local/xen.git/xen/include/xsm/xsm.h:309:19
>> (XEN) member access within null pointer of type 'struct xsm_operations'
>> (XEN) ----[ Xen-4.13-unstable x86_64 debug=y Not tainted ]----
>>
>> "adjust system domain creation (and call it earlier on x86)" didn't account
>> for the fact that domain_create() depends on XSM already being set up. There
>> is nothing very interesting which xsm_multiboot_init() more than allocating
>> memory, which means it is safe to move earlier during boot.
> Oh - perhaps it is worth pointing out that we end up following the NULL
> function pointer xsm_ops->alloc_security_domain() and execute part of
> the 16bit IVT until we end up with the retpoline explosion.
I have adjusted this portion of the commit message to read:
---8<---
"adjust system domain creation (and call it earlier on x86)" didn't account
for the fact that domain_create() depends on XSM already being set up.
Therefore, domain_create() follows xsm_ops->alloc_security_domain() which is
offset 0 from a NULL pointer, meaning that we execute the 16bit IVT until
happening to explode in __x86_indirect_thunk_rax().
There is nothing very interesting which xsm_multiboot_init() more than
allocating memory, which means it is safe to move earlier during setup.
~Andrew
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