[PATCH v14 12/19] kexec: Secure Launch kexec SEXIT support

Ross Philipson
2025-04-21T16:36:05Z

Prior to running the next kernel via kexec, the Secure Launch code
closes down private SMX resources and does an SEXIT. This allows the
next kernel to start normally without any issues starting the APs etc.

Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
---
arch/x86/kernel/slaunch.c | 72 +++++++++++++++++++++++++++++++++++++++
kernel/kexec_core.c | 4 +++
2 files changed, 76 insertions(+)

diff --git a/arch/x86/kernel/slaunch.c b/arch/x86/kernel/slaunch.c
index 94fe5e494034..b6ba4c526aa3 100644
--- a/arch/x86/kernel/slaunch.c
+++ b/arch/x86/kernel/slaunch.c
@@ -522,3 +522,75 @@ void __init slaunch_setup_txt(void)

pr_info("Intel TXT setup complete\n");
}
+
+static inline void smx_getsec_sexit(void)
+{
+ asm volatile ("getsec\n"
+ : : "a" (SMX_X86_GETSEC_SEXIT));
+}
+
+/*
+ * Used during kexec and on reboot paths to finalize the TXT state
+ * and do an SEXIT exiting the DRTM and disabling SMX mode.
+ */
+void slaunch_finalize(int do_sexit)
+{
+ u64 one = TXT_REGVALUE_ONE, val;
+ void __iomem *config;
+
+ if (!slaunch_is_txt_launch())
+ return;
+
+ config = ioremap(TXT_PRIV_CONFIG_REGS_BASE, TXT_NR_CONFIG_PAGES *
+ PAGE_SIZE);
+ if (!config) {
+ pr_emerg("Error SEXIT failed to ioremap TXT private reqs\n");
+ return;
+ }
+
+ /* Clear secrets bit for SEXIT */
+ memcpy_toio(config + TXT_CR_CMD_NO_SECRETS, &one, sizeof(one));
+ memcpy_fromio(&val, config + TXT_CR_E2STS, sizeof(val));
+
+ /* Unlock memory configurations */
+ memcpy_toio(config + TXT_CR_CMD_UNLOCK_MEM_CONFIG, &one, sizeof(one));
+ memcpy_fromio(&val, config + TXT_CR_E2STS, sizeof(val));
+
+ /* Close the TXT private register space */
+ memcpy_toio(config + TXT_CR_CMD_CLOSE_PRIVATE, &one, sizeof(one));
+ memcpy_fromio(&val, config + TXT_CR_E2STS, sizeof(val));
+
+ /*
+ * Calls to iounmap are not being done because of the state of the
+ * system this late in the kexec process. Local IRQs are disabled and
+ * iounmap causes a TLB flush which in turn causes a warning. Leaving
+ * thse mappings is not an issue since the next kernel is going to
+ * completely re-setup memory management.
+ */
+
+ /* Map public registers and do a final read fence */
+ config = ioremap(TXT_PUB_CONFIG_REGS_BASE, TXT_NR_CONFIG_PAGES *
+ PAGE_SIZE);
+ if (!config) {
+ pr_emerg("Error SEXIT failed to ioremap TXT public reqs\n");
+ return;
+ }
+
+ memcpy_fromio(&val, config + TXT_CR_E2STS, sizeof(val));
+
+ pr_emerg("TXT clear secrets bit and unlock memory complete.\n");
+
+ if (!do_sexit)
+ return;
+
+ if (smp_processor_id() != 0)
+ panic("Error TXT SEXIT must be called on CPU 0\n");
+
+ /* In case SMX mode was disabled, enable it for SEXIT */
+ cr4_set_bits(X86_CR4_SMXE);
+
+ /* Do the SEXIT SMX operation */
+ smx_getsec_sexit();
+
+ pr_info("TXT SEXIT complete.\n");
+}
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 3e62b944c883..c8c95d88eb22 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -40,6 +40,7 @@
#include <linux/hugetlb.h>
#include <linux/objtool.h>
#include <linux/kmsg_dump.h>
+#include <linux/slaunch.h>

#include <asm/page.h>
#include <asm/sections.h>
@@ -1059,6 +1060,9 @@ int kernel_kexec(void)
cpu_hotplug_enable();
pr_notice("Starting new kernel\n");
machine_shutdown();
+
+ /* Finalize TXT registers and do SEXIT */
+ slaunch_finalize(1);
}

kmsg_dump(KMSG_DUMP_SHUTDOWN);
--
2.39.3