[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2] tboot: Avoid recursive fault in early boot panic with tboot
On Thu, Jul 19, 2018 at 6:39 AM Jason Andryuk <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> Ping, Shane and Gang? > --- > v2: Correct comment and brace style > --- > xen/arch/x86/tboot.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/xen/arch/x86/tboot.c b/xen/arch/x86/tboot.c > index fb4616ae83..d5a5292d7e 100644 > --- a/xen/arch/x86/tboot.c > +++ b/xen/arch/x86/tboot.c > @@ -391,7 +391,12 @@ void tboot_shutdown(uint32_t shutdown_type) > tboot_gen_xenheap_integrity(g_tboot_shared->s3_key, &xenheap_mac); > } > > - write_ptbase(idle_vcpu[0]); > + /* > + * During early boot, we can be called by panic before idle_vcpu[0] is > + * setup, but in that case we don't need to change page tables. > + */ > + if ( idle_vcpu[0] != INVALID_VCPU ) > + write_ptbase(idle_vcpu[0]); > > ((void(*)(void))(unsigned long)g_tboot_shared->shutdown_entry)(); > > -- > 2.17.1 > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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