Re: [PATCH v2] s390/cpacf: Unpoison instruction results

On 2026-08-07 14:20, Ilya Leoshkevich wrote:
> Stop KMSAN from complaining about CPACF outputs being uninitialized.
> 
> Do not unpoison variable-length parameter blocks: mapping function
> codes (like CPACF_KIMD_SHA_256) to lengths is ugly. Let the callers
> handle this once need arises.
> 
> Signed-off-by: Ilya Leoshkevich <[email protected]>
> ---
> v1:
> https://lore.kernel.org/linux-s390/[email protected]/
> v1 -> v2: Unpoison outputs of more instructions (Sashiko).
> 

See my comment below.

>  arch/s390/include/asm/cpacf.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/s390/include/asm/cpacf.h 
> b/arch/s390/include/asm/cpacf.h
> index a83683169d98d..13d6a6344802a 100644
> --- a/arch/s390/include/asm/cpacf.h
> +++ b/arch/s390/include/asm/cpacf.h
> @@ -301,6 +301,7 @@ static __always_inline void __cpacf_query(unsigned
> int opcode,
>  					  cpacf_mask_t *mask)
>  {
>  	__cpacf_query_insn(opcode, mask, CPACF_FC_QUERY);
> +	kmsan_unpoison_memory(mask, sizeof(*mask));
>  }
> 
>  static __always_inline int __cpacf_check_opcode(unsigned int opcode)
> @@ -370,6 +371,7 @@ static __always_inline int
> cpacf_query_func(unsigned int opcode,
>  static __always_inline void __cpacf_qai(unsigned int opcode, 
> cpacf_qai_t *qai)
>  {
>  	__cpacf_query_insn(opcode, qai, CPACF_FC_QUERY_AUTH_INFO);
> +	kmsan_unpoison_memory(qai, sizeof(*qai));
>  }
> 
>  /**
> @@ -422,6 +424,7 @@ static inline int cpacf_km(unsigned long func, void 
> *param,
>  		  [opc] "i" (CPACF_KM)
>  		: "cc", "memory", "0", "1");
> 
> +	kmsan_unpoison_memory(dest, src_len - s.odd);
>  	return src_len - s.odd;
>  }
> 
> @@ -454,6 +457,7 @@ static inline int cpacf_kmc(unsigned long func, 
> void *param,
>  		  [opc] "i" (CPACF_KMC)
>  		: "cc", "memory", "0", "1");
> 
> +	kmsan_unpoison_memory(dest, src_len - s.odd);
>  	return src_len - s.odd;
>  }
> 
> @@ -587,6 +591,7 @@ static inline int cpacf_kmctr(unsigned long func,
> void *param, u8 *dest,
>  		  [opc] "i" (CPACF_KMCTR)
>  		: "cc", "memory", "0", "1");
> 
> +	kmsan_unpoison_memory(dest, src_len - s.odd);
>  	return src_len - s.odd;
>  }
> 
> @@ -619,6 +624,7 @@ static inline void cpacf_prno(unsigned long func,
> void *param,
>  		: [fc] "d" (func), [pba] "d" ((unsigned long)param),
>  		  [seed] "d" (s.pair), [opc] "i" (CPACF_PRNO)
>  		: "cc", "memory", "0", "1");
> +	kmsan_unpoison_memory(dest, dest_len);
>  }
> 
>  /**
> @@ -731,6 +737,7 @@ static inline void cpacf_kma(unsigned long func,
> void *param, u8 *dest,
>  		: [fc] "d" (func), [pba] "d" ((unsigned long)param),
>  		  [opc] "i" (CPACF_KMA)
>  		: "cc", "memory", "0", "1");
> +	kmsan_unpoison_memory(dest, src_len);

I am unhappy with this kma thing. This would only work properly with
CC 0. But CC 1 and 2 are not handled properly. However, I had a closer
look onto the AR for kma and ... well this inline function should
handle CC 1 and CC 2 somehow and it should similar to the other inline
functions return the number of bytes processed like for example 
cpacf_km().
I'll open up a bugzilla to fix this kma inline function.
If you leave out this kma hunk you can add my R-b.

>  }
> 
>  #endif	/* _ASM_S390_CPACF_H */