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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, 2023-06-15 at 22:37 +1000, Michael Ellerman wrote:
> There's code in prom_instantiate_sml() to do a "SML handover" (Stored
> Measurement Log) from OF to Linux, before Linux shuts down Open
> Firmware.
> 
> 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
> handover.
> 
> 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@ellerman.id.au>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  arch/powerpc/kernel/prom_init.c |  8 ++++++--
>  drivers/char/tpm/eventlog/of.c  | 23 ++++-------------------
>  2 files changed, 10 insertions(+), 21 deletions(-)

Split into two patches (producer and consumer).

BR, Jarkko

> 
> 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__);