[PATCH v5 22/25] powerpc/pseries: Pass PLPKS password on kexec

Andrew Donnellan
2023-01-31T06:41:06Z

From: Russell Currey <ruscur@russell.cc>

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.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>

---

v3: New patch

v4: Fix compile when CONFIG_PSERIES_PLPKS=n (snowpatch)

Fix error handling on fdt_path_offset() call (ruscur)

v5: Fix DT property name in commit message (npiggin)

Clear prop in FDT during init to prevent password exposure (mpe)

Rework to remove ifdefs from C code (npiggin)
---
arch/powerpc/include/asm/plpks.h | 14 ++++++
arch/powerpc/kernel/prom.c | 4 ++
arch/powerpc/kexec/file_load_64.c | 15 +++++--
arch/powerpc/platforms/pseries/plpks.c | 60 ++++++++++++++++++++++++++
4 files changed, 90 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/plpks.h b/arch/powerpc/include/asm/plpks.h
index 757313e00521..23b77027c916 100644
--- a/arch/powerpc/include/asm/plpks.h
+++ b/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
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 4f1c920aa13e..8a13b378770f 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/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>

@@ -893,6 +894,9 @@ 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");
diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index af8854f9eae3..3f5740fb01a4 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -27,6 +27,7 @@
#include <asm/kexec_ranges.h>
#include <asm/crashdump-ppc64.h>
#include <asm/prom.h>
+#include <asm/plpks.h>

struct umem_info {
u64 *buf; /* data buffer for usable-memory property */
@@ -977,12 +978,16 @@ 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;

+ // Make room for the PLPKS password, plus node overhead for ibm,plpks-pw.
+ if (plpks_is_available())
+ extra_size += (unsigned int)plpks_get_passwordlen() + 32;
+
if (image->type != KEXEC_TYPE_CRASH)
- return 0;
+ return extra_size;

/*
* For kdump kernel, account for linux,usable-memory and
@@ -992,7 +997,7 @@ unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
usm_entries = ((memblock_end_of_DRAM() / drmem_lmb_size()) +
(2 * (resource_size(&crashk_res) / drmem_lmb_size())));

- extra_size = (unsigned int)(usm_entries * sizeof(u64));
+ extra_size += (unsigned int)(usm_entries * sizeof(u64));

/*
* Get the number of CPU nodes in the current DT. This allows to
@@ -1230,6 +1235,10 @@ 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);
diff --git a/arch/powerpc/platforms/pseries/plpks.c b/arch/powerpc/platforms/pseries/plpks.c
index 6940280ae94a..481a669845c5 100644
--- a/arch/powerpc/platforms/pseries/plpks.c
+++ b/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 +630,57 @@ 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");
+ u8 *password;
+ int len;
+
+ if (chosen_node < 0)
+ return;
+
+ password = (u8 *)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;
--
2.39.1