[Xen-devel] [PATCH] x86: Fix boot with CONFIG_XSM enabled following c/s 7177f589ba

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

The resulting boot now looks like:

  (XEN) Using APIC driver default
  (XEN) XSM Framework v1.0.0 initialized
  (XEN) Flask: 128 avtab hash slots, 283 rules.
  (XEN) Flask: 128 avtab hash slots, 283 rules.
  (XEN) Flask:  4 users, 3 roles, 38 types, 2 bools
  (XEN) Flask:  13 classes, 283 rules
  (XEN) Flask:  Starting in enforcing mode.
  (XEN) ACPI: v5 SLEEP INFO: control[0:0], status[0:0]

and

  (XEN) Using APIC driver default
  (XEN) XSM Framework v1.0.0 initialized
  (XEN) Initialising XSM SILO mode
  (XEN) ACPI: v5 SLEEP INFO: control[0:0], status[0:0]

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/setup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 6c3a7ed..d201191 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1533,6 +1533,8 @@ void __init noreturn __start_xen(unsigned long mbi_p)
     mmio_ro_ranges = rangeset_new(NULL, "r/o mmio ranges",
                                   RANGESETF_prettyprint_hex);
 
+    xsm_multiboot_init(module_map, mbi);
+
     setup_system_domains();
 
     acpi_boot_init();
@@ -1583,8 +1585,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 
     init_IRQ();
 
-    xsm_multiboot_init(module_map, mbi);
-
     microcode_grab_module(module_map, mbi);
 
     timer_init();
-- 
2.1.4


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