powerpc/pseries: Pass PLPKS password on kexec

Before interacting with the PLPKS, we ask the hypervisor to generate a
password for the current boot, which is then required for most further
PLPKS operations.

If we kexec into a new kernel, the new kernel will try and fail to
generate a new password, as the password has already been set.

Pass the password through to the new kernel via the device tree, in
/chosen/ibm,plpks-pw. Check for the presence of this property before
trying to generate a new password - if it exists, use the existing
password and remove it from the device tree.

This only works with the kexec_file_load() syscall, not the older
kexec_load() syscall, however if you're using Secure Boot then you want
to be using kexec_file_load() anyway.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-24-ajd@linux.ibm.com

arch/powerpc/include/asm/plpks.h

@@ -176,6 +176,20 @@ u64 plpks_get_signedupdatealgorithms(void);
  */
 u16 plpks_get_passwordlen(void);
 
+/**
+ * Called in early init to retrieve and clear the PLPKS password from the DT.
+ */
+void plpks_early_init_devtree(void);
+
+/**
+ * Populates the FDT with the PLPKS password to prepare for kexec.
+ */
+int plpks_populate_fdt(void *fdt);
+#else // CONFIG_PSERIES_PLPKS
+static inline bool plpks_is_available(void) { return false; }
+static inline u16 plpks_get_passwordlen(void) { BUILD_BUG(); }
+static inline void plpks_early_init_devtree(void) { }
+static inline int plpks_populate_fdt(void *fdt) { BUILD_BUG(); }
 #endif // CONFIG_PSERIES_PLPKS
 
 #endif // _ASM_POWERPC_PLPKS_H

arch/powerpc/kernel/prom.c

@@ -56,6 +56,7 @@
 #include <asm/drmem.h>
 #include <asm/ultravisor.h>
 #include <asm/prom.h>
+#include <asm/plpks.h>
 
 #include <mm/mmu_decl.h>
 
@@ -887,6 +888,9 @@ void __init early_init_devtree(void *params)
 		powerpc_firmware_features |= FW_FEATURE_PS3_POSSIBLE;
 #endif
 
+	/* If kexec left a PLPKS password in the DT, get it and clear it */
+	plpks_early_init_devtree();
+
 	tm_init();
 
 	DBG(" <- early_init_devtree()\n");

arch/powerpc/kexec/file_load_64.c

@@ -28,6 +28,7 @@
 #include <asm/crashdump-ppc64.h>
 #include <asm/mmzone.h>
 #include <asm/prom.h>
+#include <asm/plpks.h>
 
 struct umem_info {
 	u64 *buf;		/* data buffer for usable-memory property */
@@ -978,12 +979,17 @@ static unsigned int cpu_node_size(void)
  */
 unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
 {
-	unsigned int cpu_nodes, extra_size;
+	unsigned int cpu_nodes, extra_size = 0;
 	struct device_node *dn;
 	u64 usm_entries;
 
+	// Budget some space for the password blob. There's already extra space
+	// for the key name
+	if (plpks_is_available())
+		extra_size += (unsigned int)plpks_get_passwordlen();
+
 	if (image->type != KEXEC_TYPE_CRASH)
-		return 0;
+		return extra_size;
 
 	/*
 	 * For kdump kernel, account for linux,usable-memory and
@@ -993,9 +999,7 @@ unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
 	if (drmem_lmb_size()) {
 		usm_entries = ((memory_hotplug_max() / drmem_lmb_size()) +
 			       (2 * (resource_size(&crashk_res) / drmem_lmb_size())));
-		extra_size = (unsigned int)(usm_entries * sizeof(u64));
-	} else {
-		extra_size = 0;
+		extra_size += (unsigned int)(usm_entries * sizeof(u64));
 	}
 
 	/*
@@ -1234,6 +1238,10 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
 		}
 	}
 
+	// If we have PLPKS active, we need to provide the password to the new kernel
+	if (plpks_is_available())
+		ret = plpks_populate_fdt(fdt);
+
 out:
 	kfree(rmem);
 	kfree(umem);

arch/powerpc/platforms/pseries/plpks.c

@@ -16,6 +16,9 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/of_fdt.h>
+#include <linux/libfdt.h>
+#include <linux/memblock.h>
 #include <asm/hvcall.h>
 #include <asm/machdep.h>
 #include <asm/plpks.h>
@@ -128,6 +131,12 @@ static int plpks_gen_password(void)
 	u8 *password, consumer = PLPKS_OS_OWNER;
 	int rc;
 
+	// If we booted from kexec, we could be reusing an existing password already
+	if (ospassword) {
+		pr_debug("Password of length %u already in use\n", ospasswordlength);
+		return 0;
+	}
+
 	// The password must not cross a page boundary, so we align to the next power of 2
 	password = kzalloc(roundup_pow_of_two(maxpwsize), GFP_KERNEL);
 	if (!password)
@@ -621,6 +630,58 @@ int plpks_read_bootloader_var(struct plpks_var *var)
 	return plpks_read_var(PLPKS_BOOTLOADER_OWNER, var);
 }
 
+int plpks_populate_fdt(void *fdt)
+{
+	int chosen_offset = fdt_path_offset(fdt, "/chosen");
+
+	if (chosen_offset < 0) {
+		pr_err("Can't find chosen node: %s\n",
+		       fdt_strerror(chosen_offset));
+		return chosen_offset;
+	}
+
+	return fdt_setprop(fdt, chosen_offset, "ibm,plpks-pw", ospassword, ospasswordlength);
+}
+
+// Once a password is registered with the hypervisor it cannot be cleared without
+// rebooting the LPAR, so to keep using the PLPKS across kexec boots we need to
+// recover the previous password from the FDT.
+//
+// There are a few challenges here.  We don't want the password to be visible to
+// users, so we need to clear it from the FDT.  This has to be done in early boot.
+// Clearing it from the FDT would make the FDT's checksum invalid, so we have to
+// manually cause the checksum to be recalculated.
+void __init plpks_early_init_devtree(void)
+{
+	void *fdt = initial_boot_params;
+	int chosen_node = fdt_path_offset(fdt, "/chosen");
+	const u8 *password;
+	int len;
+
+	if (chosen_node < 0)
+		return;
+
+	password = fdt_getprop(fdt, chosen_node, "ibm,plpks-pw", &len);
+	if (len <= 0) {
+		pr_debug("Couldn't find ibm,plpks-pw node.\n");
+		return;
+	}
+
+	ospassword = memblock_alloc_raw(len, SMP_CACHE_BYTES);
+	if (!ospassword) {
+		pr_err("Error allocating memory for password.\n");
+		goto out;
+	}
+
+	memcpy(ospassword, password, len);
+	ospasswordlength = (u16)len;
+
+out:
+	fdt_nop_property(fdt, chosen_node, "ibm,plpks-pw");
+	// Since we've cleared the password, we must update the FDT checksum
+	early_init_dt_verify(fdt);
+}
+
 static __init int pseries_plpks_init(void)
 {
 	int rc;