Re: [RFC PATCH v2 1/3] powerpc/prom_init: Replace linux,sml-base/sml-size with linux,sml-log

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 11/03/2024 à 14:20, Stefan Berger a écrit :
> linux,sml-base holds the address of a buffer with the TPM log. This
> buffer may become invalid after a kexec. To avoid accessing an invalid
> address or corrupted buffer, embed the whole TPM log in the device tree
> property linux,sml-log. This helps to protect the log since it is
> properly carried across a kexec soft reboot with both of the kexec
> syscalls.
> 
> Avoid having the firmware ingest the whole TPM log when calling
> prom_setprop but only create the linux,sml-log property as a place holder.
> Insert the actual TPM log during the tree flattening phase.
> 
> Fixes: 4a727429abec ("PPC64: Add support for instantiating SML from Open Firmware")
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>   arch/powerpc/kernel/prom_init.c | 27 +++++++++++++++++++--------
>   1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index e67effdba85c..6f7ca72013c2 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -211,6 +211,8 @@ static cell_t __prombss regbuf[1024];
>   
>   static bool  __prombss rtas_has_query_cpu_stopped;
>   
> +static u64 __prombss sml_base;
> +static u32 __prombss sml_size;
>   
>   /*
>    * Error results ... some OF calls will return "-1" on error, some
> @@ -1954,17 +1956,15 @@ static void __init prom_instantiate_sml(void)
>   	}
>   	prom_printf(" done\n");
>   
> -	reserve_mem(base, size);
> -
> -	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-base",
> -		     &base, sizeof(base));
> -	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-size",
> -		     &size, sizeof(size));
> -
> -	prom_debug("sml base     = 0x%llx\n", base);
> +	/* Add property now, defer adding log to tree flattening phase */
> +	prom_setprop(ibmvtpm_node, "/vdevice/vtpm", "linux,sml-log",
> +		     NULL, 0);
>   	prom_debug("sml size     = 0x%x\n", size);
>   
>   	prom_debug("prom_instantiate_sml: end...\n");
> +
> +	sml_base = base;
> +	sml_size = size;
>   }
>   
>   /*
> @@ -2645,6 +2645,17 @@ static void __init scan_dt_build_struct(phandle node, unsigned long *mem_start,
>   		}
>   		prev_name = sstart + soff;
>   
> +		if (!prom_strcmp("linux,sml-log", pname)) {
> +			/* push property head */
> +			dt_push_token(OF_DT_PROP, mem_start, mem_end);
> +			dt_push_token(sml_size, mem_start, mem_end);
> +			dt_push_token(soff, mem_start, mem_end);
> +			/* push property content */
> +			valp = make_room(mem_start, mem_end, sml_size, 1);
> +			memcpy(valp, (void *)sml_base, sml_size);

You can't cast a u64 into a pointer. If sml_base is an address, it must 
be declared as an unsigned long.

Build with pmac32_defconfig :

   CC      arch/powerpc/kernel/prom_init.o
arch/powerpc/kernel/prom_init.c: In function 'scan_dt_build_struct':
arch/powerpc/kernel/prom_init.c:2663:38: error: cast to pointer from 
integer of different size [-Werror=int-to-pointer-cast]
  2663 |                         memcpy(valp, (void *)sml_base, sml_size);
       |                                      ^
cc1: all warnings being treated as errors
make[4]: *** [scripts/Makefile.build:243: 
arch/powerpc/kernel/prom_init.o] Error 1


> +			*mem_start = ALIGN(*mem_start, 4);
> +			continue;
> +		}
>   		/* get length */
>   		l = call_prom("getproplen", 2, 1, node, pname);
>