Subject: Re: [PATCH] firmware: arm_ffa: honor descriptor size in PARTITION_INFO_GET_REGS

From: Sudeep Holla <[email-masked]>
Date: Thu, 14 May 2026 10:31:23 +0100

On Tue, May 12, 2026 at 08:28:00PM -0700, Jamie Nguyen wrote:
> __ffa_partition_info_get_regs() walks the response with a hardcoded
> 24-byte stride (regs += 3) even though the SPMC tells us the actual
> per-descriptor size via PARTITION_INFO_SZ in x2[63:48]. The size is
> read into buf_sz and then thrown away.
> 
> That works while every SPMC returns the FF-A v1.1 layout, but it falls
> apart against a v1.3 SPMC returning the 48-byte descriptor. The loop
> strides over half a descriptor at a time and ends up parsing every
> other entry from a slice of two adjacent ones.
> 
> The FF-A spec (v1.2, section 18.5) says that the producer should
> report the descriptor size, and the consumer is supposed to stride by
> that size and ignore any trailing fields it doesn't understand. The
> non-REGS path (__ffa_partition_info_get) does this already, and the
> REGS path should match.
> 
> Use buf_sz for the stride, and bail out with -EPROTO if the SPMC
> reports something we can't safely walk.
> 
> Fixes: 7bc0f589c81d ("firmware: arm_ffa: Fix big-endian support in __ffa_partition_info_regs_get()")
> Signed-off-by: Jamie Nguyen <[email-masked]>
> ---
>  drivers/firmware/arm_ffa/driver.c | 35 ++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
> index c72ee4756585..b712e8a03dab 100644
> --- a/drivers/firmware/arm_ffa/driver.c
> +++ b/drivers/firmware/arm_ffa/driver.c
> @@ -321,6 +321,22 @@ __ffa_partition_info_get(u32 uuid0, u32 uuid1, u32 uuid2, u32 uuid3,
>  #define PART_INFO_ID(x)		((u16)(FIELD_GET(PART_INFO_ID_MASK, (x))))
>  #define PART_INFO_EXEC_CXT(x)	((u16)(FIELD_GET(PART_INFO_EXEC_CXT_MASK, (x))))
>  #define PART_INFO_PROPERTIES(x)	((u32)(FIELD_GET(PART_INFO_PROPS_MASK, (x))))
> +
> +/*
> + * FF-A v1.2 section 13.9 Table 13.40: registers x3..x17 carry the partition
> + * descriptors, i.e. 15 u64 of payload per FFA_PARTITION_INFO_GET_REGS call.
> + */
> +#define FFA_PART_INFO_REGS_PAYLOAD_U64	15
> +
> +/*
> + * FF-A v1.1 partition information descriptor (FF-A v1.2 section 6.2.1
> + * Table 6.1): id (2) + exec_ctxt (2) + properties (4) + UUID (16) = 24
> + * bytes. This is the minimum size the SPMC must report; the kernel reads
> + * exactly these fields and ignores any trailing ones per the forward-
> + * compatibility rules in FF-A v1.2 section 18.5.
> + */

I can't see any such details is the above mention version and section.
Can you confirm you are looking at [1] ?

-- 
Regards,
Sudeep

[1] https://developer.arm.com/documentation/den0077/j