[PATCH v6 16/22] powerpc/book3s64/kuap: Improve error reporting with KUAP

[Christophe Leroy]

Le 25/11/2020 à 06:16, Aneesh Kumar K.V a écrit :
> With hash translation use DSISR_KEYFAULT to identify a wrong access.
> With Radix we look at the AMR value and type of fault.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/32/kup.h     |  4 +--
>   arch/powerpc/include/asm/book3s/64/kup.h     | 27 ++++++++++++++++----
>   arch/powerpc/include/asm/kup.h               |  4 +--
>   arch/powerpc/include/asm/nohash/32/kup-8xx.h |  4 +--
>   arch/powerpc/mm/fault.c                      |  2 +-
>   5 files changed, 29 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
> index 32fd4452e960..b18cd931e325 100644
> --- a/arch/powerpc/include/asm/book3s/32/kup.h
> +++ b/arch/powerpc/include/asm/book3s/32/kup.h
> @@ -177,8 +177,8 @@ static inline void restore_user_access(unsigned long flags)
>   		allow_user_access(to, to, end - addr, KUAP_READ_WRITE);
>   }
>   
> -static inline bool
> -bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
> +static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
> +				  bool is_write, unsigned long error_code)
>   {
>   	unsigned long begin = regs->kuap & 0xf0000000;
>   	unsigned long end = regs->kuap << 28;
> diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
> index 4a3d0d601745..2922c442a218 100644
> --- a/arch/powerpc/include/asm/book3s/64/kup.h
> +++ b/arch/powerpc/include/asm/book3s/64/kup.h
> @@ -301,12 +301,29 @@ static inline void set_kuap(unsigned long value)
>   	isync();
>   }
>   
> -static inline bool
> -bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
> +#define RADIX_KUAP_BLOCK_READ	UL(0x4000000000000000)
> +#define RADIX_KUAP_BLOCK_WRITE	UL(0x8000000000000000)
> +
> +static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
> +				  bool is_write, unsigned long error_code)
>   {
> -	return WARN(mmu_has_feature(MMU_FTR_KUAP) &&
> -		    (regs->kuap & (is_write ? AMR_KUAP_BLOCK_WRITE : AMR_KUAP_BLOCK_READ)),
> -		    "Bug: %s fault blocked by AMR!", is_write ? "Write" : "Read");
> +	if (!mmu_has_feature(MMU_FTR_KUAP))
> +		return false;
> +
> +	if (radix_enabled()) {
> +		/*
> +		 * Will be a storage protection fault.
> +		 * Only check the details of AMR[0]
> +		 */
> +		return WARN((regs->kuap & (is_write ? RADIX_KUAP_BLOCK_WRITE : RADIX_KUAP_BLOCK_READ)),
> +			    "Bug: %s fault blocked by AMR!", is_write ? "Write" : "Read");

I think it is pointless to keep the WARN() here.

I have a series aiming at removing them. See 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/cc9129bdda1dbc2f0a09cf45fece7d0b0e690784.1605541983.git.christophe.leroy@csgroup.eu/

> +	}
> +	/*
> +	 * We don't want to WARN here because userspace can setup
> +	 * keys such that a kernel access to user address can cause
> +	 * fault
> +	 */
> +	return !!(error_code & DSISR_KEYFAULT);
>   }
>   
>   static __always_inline void allow_user_access(void __user *to, const void __user *from,
> diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
> index a06e50b68d40..952be0414f43 100644
> --- a/arch/powerpc/include/asm/kup.h
> +++ b/arch/powerpc/include/asm/kup.h
> @@ -59,8 +59,8 @@ void setup_kuap(bool disabled);
>   #else
>   static inline void setup_kuap(bool disabled) { }
>   
> -static inline bool
> -bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
> +static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
> +				  bool is_write, unsigned long error_code)
>   {
>   	return false;
>   }
> diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
> index 567cdc557402..7bdd9e5b63ed 100644
> --- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
> +++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
> @@ -60,8 +60,8 @@ static inline void restore_user_access(unsigned long flags)
>   	mtspr(SPRN_MD_AP, flags);
>   }
>   
> -static inline bool
> -bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
> +static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
> +				  bool is_write, unsigned long error_code)
>   {
>   	return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xff000000),
>   		    "Bug: fault blocked by AP register !");
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 0add963a849b..c91621df0c61 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -227,7 +227,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
>   
>   	// Read/write fault in a valid region (the exception table search passed
>   	// above), but blocked by KUAP is bad, it can never succeed.
> -	if (bad_kuap_fault(regs, address, is_write))
> +	if (bad_kuap_fault(regs, address, is_write, error_code))
>   		return true;
>   
>   	// What's left? Kernel fault on user in well defined regions (extable
>