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From 7ca58fbef489fcb17631872a2bdc929823a2a494 Mon Sep 17 00:00:00 2001
From: Jason Andryuk <jandryuk@gmail.com>
Date: Tue, 5 Sep 2023 08:52:33 +0200
Subject: [PATCH 25/55] tboot: Disable CET at shutdown
tboot_shutdown() calls into tboot to perform the actual system shutdown.
tboot isn't built with endbr annotations, and Xen has CET-IBT enabled on
newer hardware. shutdown_entry isn't annotated with endbr and Xen
faults:
Panic on CPU 0:
CONTROL-FLOW PROTECTION FAULT: #CP[0003] endbranch
And Xen hangs at this point.
Disabling CET-IBT let Xen and tboot power off, but reboot was
perfoming a poweroff instead of a warm reboot. Disabling all of CET,
i.e. shadow stacks as well, lets tboot reboot properly.
Fixes: cdbe2b0a1aec ("x86: Enable CET Indirect Branch Tracking")
Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>
master commit: 0801868f550539d417d46f82c49307480947ccaa
master date: 2023-08-17 16:24:49 +0200
---
xen/arch/x86/tboot.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/xen/arch/x86/tboot.c b/xen/arch/x86/tboot.c
index fe1abfdf08..a2e9e97ed7 100644
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -398,6 +398,16 @@ void tboot_shutdown(uint32_t shutdown_type)
tboot_gen_xenheap_integrity(g_tboot_shared->s3_key, &xenheap_mac);
}
+ /*
+ * Disable CET - tboot may not be built with endbr, and it doesn't support
+ * shadow stacks.
+ */
+ if ( read_cr4() & X86_CR4_CET )
+ {
+ wrmsrl(MSR_S_CET, 0);
+ write_cr4(read_cr4() & ~X86_CR4_CET);
+ }
+
/*
* 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.
--
2.42.0
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