linux-kernel - Re: [PATCH v8 7/7] powerpc: add machine check safe copy_to

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Message-ID: <87lfw1s6u0.fsf@concordia.ellerman.id.au>
Date:   Sat, 10 Aug 2019 19:33:27 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Santosh Sivaraj <santosh@...six.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        christophe leroy <christophe.leroy@....fr>
Subject: Re: [PATCH v8 7/7] powerpc: add machine check safe copy_to_user

Santosh Sivaraj <santosh@...six.org> writes:
> Use  memcpy_mcsafe() implementation to define copy_to_user_mcsafe()
>
> Signed-off-by: Santosh Sivaraj <santosh@...six.org>
> ---
>  arch/powerpc/Kconfig               |  1 +
>  arch/powerpc/include/asm/uaccess.h | 14 ++++++++++++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 77f6ebf97113..4316e36095a2 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -137,6 +137,7 @@ config PPC
>  	select ARCH_HAS_STRICT_KERNEL_RWX	if ((PPC_BOOK3S_64 || PPC32) && !RELOCATABLE && !HIBERNATION)
>  	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
>  	select ARCH_HAS_UACCESS_FLUSHCACHE	if PPC64
> +	select ARCH_HAS_UACCESS_MCSAFE		if PPC64
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARCH_HAVE_NMI_SAFE_CMPXCHG
>  	select ARCH_KEEP_MEMBLOCK
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 8b03eb44e876..15002b51ff18 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -387,6 +387,20 @@ static inline unsigned long raw_copy_to_user(void __user *to,
>  	return ret;
>  }
>  
> +static __always_inline unsigned long __must_check
> +copy_to_user_mcsafe(void __user *to, const void *from, unsigned long n)
> +{
> +	if (likely(check_copy_size(from, n, true))) {
> +		if (access_ok(to, n)) {
> +			allow_write_to_user(to, n);
> +			n = memcpy_mcsafe((void *)to, from, n);
> +			prevent_write_to_user(to, n);
> +		}
> +	}
> +
> +	return n;
> +}

This looks OK to me.

It would be nice though if copy_to_user_mcsafe() followed the pattern of
the other copy_to_user() etc. routines where the arch code is only
responsible for the actual arch details, and all the checks are done in
the generic code. That would be a good cleanup to do after this has gone
in, as the 2nd implementation of the API.

cheers