Re: [PATCH] powerpc/prom: Fix "ibm,arch-vec-5-platform-support" scan

[Fabiano Rosas <farosas@linux.ibm.com>]

Cédric Le Goater <clg@kaod.org> writes:

> The "ibm,arch-vec-5-platform-support" property is a list of pairs of
> bytes representing the options and values supported by the platform
> firmware. At boot time, Linux scans this list and activates the
> available features it recognizes : Radix and XIVE.
>
> A recent change modified the number of entries to loop on and 8 bytes,
> 4 pairs of { options, values } entries are always scanned. This is
> fine on KVM but not on PowerVM which can advertises less. As a
> consequence on this platform, Linux reads extra entries pointing to
> random data, interprets these as available features and tries to
> activate them, leading to a firmware crash in
> ibm,client-architecture-support.
>
> Fix that by using the property length of "ibm,arch-vec-5-platform-support".
>
> Cc: stable@vger.kernel.org # v4.20+
> Fixes: ab91239942a9 ("powerpc/prom: Remove VLA in prom_check_platform_support()")
> Signed-off-by: Cédric Le Goater <clg@kaod.org>

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

> ---
>  arch/powerpc/kernel/prom_init.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index e9d4eb6144e1..ccf77b985c8f 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -1331,14 +1331,10 @@ static void __init prom_check_platform_support(void)
>  		if (prop_len > sizeof(vec))
>  			prom_printf("WARNING: ibm,arch-vec-5-platform-support longer than expected (len: %d)\n",
>  				    prop_len);
> -		prom_getprop(prom.chosen, "ibm,arch-vec-5-platform-support",
> -			     &vec, sizeof(vec));
> -		for (i = 0; i < sizeof(vec); i += 2) {
> -			prom_debug("%d: index = 0x%x val = 0x%x\n", i / 2
> -								  , vec[i]
> -								  , vec[i + 1]);
> -			prom_parse_platform_support(vec[i], vec[i + 1],
> -						    &supported);
> +		prom_getprop(prom.chosen, "ibm,arch-vec-5-platform-support", &vec, sizeof(vec));
> +		for (i = 0; i < prop_len; i += 2) {
> +			prom_debug("%d: index = 0x%x val = 0x%x\n", i / 2, vec[i], vec[i + 1]);
> +			prom_parse_platform_support(vec[i], vec[i + 1], &supported);
>  		}
>  	}