On 24/03/2025 1:37 pm, Jan Beulich wrote:
> On 21.03.2025 10:26, Sergiy Kibrik wrote:
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -695,9 +695,12 @@ int hvm_domain_initialise(struct domain *d,
>> if ( hvm_tsc_scaling_supported )
>> d->arch.hvm.tsc_scaling_ratio = hvm_default_tsc_scaling_ratio;
>>
>> - rc = viridian_domain_init(d);
>> - if ( rc )
>> - goto fail2;
>> + if ( is_viridian_domain(d) )
>> + {
>> + rc = viridian_domain_init(d);
>> + if ( rc )
>> + goto fail2;
>> + }
> It is, aiui, this conditional initialization which causes
>
> (XEN) [ 9.136463] UBSAN: Undefined behaviour in
> arch/x86/hvm/viridian/viridian.c:1118:43
> (XEN) [ 9.136465] member access within null pointer of type 'const struct
> viridian_domain'
> (XEN) [ 9.136471] ----[ Xen-4.21-unstable x86_64 debug=y ubsan=y Not
> tainted ]----
> (XEN) [ 9.136473] CPU: 14
> (XEN) [ 9.136475] RIP: e008:[<ffff82d04032e8a8>]
> common/ubsan/ubsan.c#ubsan_epilogue+0xa/0xd9
> (XEN) [ 9.136480] RFLAGS: 0000000000010096 CONTEXT: hypervisor (d0v6)
> (XEN) [ 9.136484] rax: 0000000000000000 rbx: ffff8304761afb40 rcx:
> 0000000000000868
> (XEN) [ 9.136486] rdx: ffff8304761affd0 rsi: 0000000000000004 rdi:
> ffff8304761afb40
> (XEN) [ 9.136488] rbp: ffff8304761afb30 rsp: ffff8304761afb20 r8:
> 0000000000000006
> (XEN) [ 9.136490] r9: 00000000ffffffff r10: 0000000000000000 r11:
> 0000000000000000
> (XEN) [ 9.136493] r12: ffff82d040913d22 r13: 0000000000000003 r14:
> ffff82d040b237a0
> (XEN) [ 9.136495] r15: 000000000000000f cr0: 0000000080050033 cr4:
> 0000000000b526e0
> (XEN) [ 9.136497] cr3: 0000000308528000 cr2: 00007f24a0c9de28
> (XEN) [ 9.136499] fsb: 00007f24a3fd6b48 gsb: ffff8881b9b80000 gss:
> 0000000000000000
> (XEN) [ 9.136501] ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e010
> cs: e008
> (XEN) [ 9.136505] Xen code around <ffff82d04032e8a8>
> (common/ubsan/ubsan.c#ubsan_epilogue+0xa/0xd9):
> (XEN) [ 9.136507] 89 e5 41 54 53 48 89 fb <0f> 0b 48 8d 3d ff 92 37 00 e8
> 9d 99 00 00 48 85
> (XEN) [ 9.136572] Xen stack trace from rsp=ffff8304761afb20:
> (XEN) [ 9.136574] 0000000000000003 ffff82d040913d22 ffff8304761afb70
> ffff82d04032ef58
> (XEN) [ 9.136578] 0000000000000202 ffff82d040911100 0000000000000000
> 0000000000000000
> (XEN) [ 9.136581] ffff82d040b237a0 000000000000000f ffff8304761afbd0
> ffff82d04032f3af
> (XEN) [ 9.136585] ffff82d0406b8900 0000002b8000045e ffff82d040913d1e
> 0000000000000001
> (XEN) [ 9.136588] ffff82d040b23703 000000000000000f ffff8304761afbc0
> ffff830405d65000
> (XEN) [ 9.136592] ffff8304761afd00 0000000000000000 ffff8304761afc18
> ffff82d040418b9c
> (XEN) [ 9.136595] 0000000000000000 0000000000000000 0000000000000000
> 0000000000000000
> (XEN) [ 9.136598] ffff82d040b23a88 00000000000002e8 ffff830401d6cfe0
> ffff8304761afc98
> (XEN) [ 9.136602] ffff82d04045fc14 00000000000002c0 ffff82d040b23a58
> ffff8304761afd00
> (XEN) [ 9.136605] ffff82d040418a0a ffff830405d65000 ffff82d040b23a88
> 0000000154381286
> (XEN) [ 9.136609] 0000000000000000 00383ffe00090672 0000000000001c78
> fffffffffffffff4
> (XEN) [ 9.136612] ffff830476161000 ffff8304761afdb0 ffff830405d65000
> ffff8304761afd50
> (XEN) [ 9.136616] ffff82d040630690 800000030847e127 0000000000000206
> 000000000000000e
> (XEN) [ 9.136619] ffff82d040a00b44 ffff82d040a00b40 ffff82d040a00b44
> ffff83047618f000
> (XEN) [ 9.136622] 00007f24a3c7a010 ffff8304761afef8 ffff8304761afef8
> ffff8304761b5088
> (XEN) [ 9.136626] 00001c7800000580 ffff830483a24000 0000000000000001
> 00007f24a3c7a010
> (XEN) [ 9.136629] 0000000000000001 ffff830405d65000 00007f24a3c7a010
> 0000000000000001
> (XEN) [ 9.136633] 0000000000000021 0000000000000000 ffff8304761afe68
> ffff82d0402c662f
> (XEN) [ 9.136636] ffff8304761afd80 ffff82d0405a0fbb ffff830476161000
> ffff8881b9b80000
> (XEN) [ 9.136640] ffff8304761afdb8 ffff82d04052fdef ffff830476161000
> ffff8881b9b80000
> (XEN) [ 9.136643] Xen call trace:
> (XEN) [ 9.136646] [<ffff82d04032e8a8>] R
> common/ubsan/ubsan.c#ubsan_epilogue+0xa/0xd9
> (XEN) [ 9.136648] [<ffff82d04032ef58>] F
> __ubsan_handle_type_mismatch+0x135/0x48e
> (XEN) [ 9.136651] [<ffff82d04032f3af>] F
> __ubsan_handle_type_mismatch_v1+0xfe/0x100
> (XEN) [ 9.136655] [<ffff82d040418b9c>] F
> arch/x86/hvm/viridian/viridian.c#viridian_save_domain_ctxt+0x192/0x204
> (XEN) [ 9.136658] [<ffff82d04045fc14>] F hvm_save+0x4d1/0x5c6
> (XEN) [ 9.136661] [<ffff82d040630690>] F arch_do_domctl+0x2f8/0x51aa
> (XEN) [ 9.136664] [<ffff82d0402c662f>] F do_domctl+0xc91/0x460d
> (XEN) [ 9.136667] [<ffff82d04053ab70>] F pv_hypercall+0x6d6/0x834
> (XEN) [ 9.136669] [<ffff82d0402012d3>] F lstar_enter+0x143/0x150
> (XEN) [ 9.136671]
> (XEN) [ 9.136673]
> ================================================================================
> (XEN) [ 9.622282]
> (XEN) [ 9.624469] ****************************************
> (XEN) [ 9.630471] Panic on CPU 14:
> (XEN) [ 9.634182] UBSAN failure detected
> (XEN) [ 9.638469] ****************************************
>
> throughout tests on actual hardware in CI. And really I don't think it's just
> UB, but
> rather a real NULL deref:
This is a consequence of us turning on UBSAN generally in GitlabCI, and
will be the norm moving forward.
Nevertheless, "member access within null pointer of type $X" is very
clear cut.
~Andrew
