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

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

On 7/10/23 17:23, Jarkko Sakkinen wrote:
> 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@xxxxxxxxxxxxxx>
> > Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> > ---
> >   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).

I think this wouldn't be right since it would break the system when only one patch is applied since it would be reading the fields in the wrong endianess.

    Stefan
> 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__);