[PATCH v2 1/2] powerpc/tpm: Create linux,sml-base/size as big endian

Michael Ellerman mpe at ellerman.id.au
Thu Jun 15 22:37:02 AEST 2023

There's code in prom_instantiate_sml() to do a "SML handover" (Stored
Measurement Log) from OF to Linux, before Linux shuts down Open

This involves creating a buffer to hold the SML, and creating two device
tree properties to record its base address and size. The kernel then
later reads those properties from the device tree to find the SML.

When the code was initially added in commit 4a727429abec ("PPC64: Add
support for instantiating SML from Open Firmware") the powerpc kernel
was always built big endian, so the properties were created big endian
by default.

However since then little endian support was added to powerpc, and now
the code lacks conversions to big endian when creating the properties.

This means on little endian kernels the device tree properties are
little endian, which is contrary to the device tree spec, and in
contrast to all other device tree properties.

To cope with that a workaround was added in tpm_read_log_of() to skip
the endian conversion if the properties were created via the SML

A better solution is to encode the properties as big endian as they
should be, and remove the workaround.

Typically changing the encoding of a property like this would present
problems for kexec. However the SML is not propagated across kexec, so
changing the encoding of the properties is a non-issue.

Fixes: e46e22f12b19 ("tpm: enhance read_log_of() to support Physical TPM event log")
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>
 arch/powerpc/kernel/prom_init.c |  8 ++++++--
 drivers/char/tpm/eventlog/of.c  | 23 ++++-------------------
 2 files changed, 10 insertions(+), 21 deletions(-)

v2: Add Stefan's reviewed-by.

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index d464ba412084..72fe306b6820 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -1900,6 +1900,7 @@ static void __init prom_instantiate_sml(void)
 	u32 entry = 0, size = 0, succ = 0;
 	u64 base;
 	__be32 val;
+	__be64 val64;
 	prom_debug("prom_instantiate_sml: start...\n");
@@ -1956,10 +1957,13 @@ static void __init prom_instantiate_sml(void)
 	reserve_mem(base, size);
+	val64 = cpu_to_be64(base);
 	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-base",
-		     &base, sizeof(base));
+		     &val64, sizeof(val64));
+	val = cpu_to_be32(size);
 	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-size",
-		     &size, sizeof(size));
+		     &val, sizeof(val));
 	prom_debug("sml base     = 0x%llx\n", base);
 	prom_debug("sml size     = 0x%x\n", size);
diff --git a/drivers/char/tpm/eventlog/of.c b/drivers/char/tpm/eventlog/of.c
index 930fe43d5daf..0bc0cb6333c6 100644
--- a/drivers/char/tpm/eventlog/of.c
+++ b/drivers/char/tpm/eventlog/of.c
@@ -51,8 +51,8 @@ static int tpm_read_log_memory_region(struct tpm_chip *chip)
 int tpm_read_log_of(struct tpm_chip *chip)
 	struct device_node *np;
-	const u32 *sizep;
-	const u64 *basep;
+	const __be32 *sizep;
+	const __be64 *basep;
 	struct tpm_bios_log *log;
 	u32 size;
 	u64 base;
@@ -73,23 +73,8 @@ int tpm_read_log_of(struct tpm_chip *chip)
 	if (sizep == NULL || basep == NULL)
 		return -EIO;
-	/*
-	 * For both vtpm/tpm, firmware has log addr and log size in big
-	 * endian format. But in case of vtpm, there is a method called
-	 * sml-handover which is run during kernel init even before
-	 * device tree is setup. This sml-handover function takes care
-	 * of endianness and writes to sml-base and sml-size in little
-	 * endian format. For this reason, vtpm doesn't need conversion
-	 * but physical tpm needs the conversion.
-	 */
-	if (of_property_match_string(np, "compatible", "IBM,vtpm") < 0 &&
-	    of_property_match_string(np, "compatible", "IBM,vtpm20") < 0) {
-		size = be32_to_cpup((__force __be32 *)sizep);
-		base = be64_to_cpup((__force __be64 *)basep);
-	} else {
-		size = *sizep;
-		base = *basep;
-	}
+	size = be32_to_cpup(sizep);
+	base = be64_to_cpup(basep);
 	if (size == 0) {
 		dev_warn(&chip->dev, "%s: Event log area empty\n", __func__);

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