Re: [Xen-devel] [PATCH v2] tboot: Avoid recursive fault in early boot panic with tboot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.07.18 at 12:39, <jandryuk@xxxxxxxxx> wrote:
> If panic is called before init_idle_domain on a tboot-launched system,
> then Xen recursively faults in write_ptbase as seen below.
> 
> (XEN)    [<ffff82d080286690>] write_ptbase+0/0x10
> (XEN)    [<ffff82d0802c4c3b>] tboot_shutdown+0x6b/0x260
> (XEN)    [<ffff82d08029ddac>] machine_restart+0xac/0x2d0
> (XEN)    [<ffff82d080286690>] write_ptbase+0/0x10
> (XEN)    [<ffff82d0802446c1>] panic+0x111/0x120
> (XEN)    [<ffff82d0802a51c1>] do_general_protection+0x171/0x1f0
> (XEN)    [<ffff82d080287a82>] mm.c#virt_to_xen_l2e+0x12/0x1c0
> (XEN)    [<ffff82d080354720>] x86_64/entry.S#handle_exception_saved+0x66/0xa4
> (XEN)    [<ffff82d080286690>] write_ptbase+0/0x10
> (XEN)    [<ffff82d0802c4c3b>] tboot_shutdown+0x6b/0x260
> (XEN)    [<ffff82d08029ddac>] machine_restart+0xac/0x2d0
> (XEN)    [<ffff82d0802446c1>] panic+0x111/0x120
> (XEN)    [<ffff82d0803c11a0>] setup.c#bootstrap_map+0/0x11a
> (XEN)    [<ffff82d0803b82a0>] flask_op.c#parse_flask_param+0/0xb0
> (XEN)    [<ffff82d0803c11a0>] setup.c#bootstrap_map+0/0x11a
> (XEN)    [<ffff82d0803b6f6c>] xsm_multiboot_init+0x7c/0xb0
> (XEN)    [<ffff82d0803c34bb>] __start_xen+0x1d2b/0x2da0
> (XEN)    [<ffff82d0802000f3>] __high_start+0x53/0x60
> 
> idle_vcpu[0] is still poisoned with INVALID_VCPU, so write_ptbase faults
> dereferencing the pointer.  This fault calls panic and recurses through
> the same code path.
> 
> If tboot_shutdown is called while idle_vcpu[0] == INVALID_VCPU, then we
> are still operating with the initial page tables.  Therefore changing
> page tables with write_ptbase is unnecessary.
> 
> An easy way to reproduce this is to use tboot to launch an XSM-enabled
> Xen without an XSM policy.
> 
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel