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Date:   Wed, 6 Apr 2022 12:22:43 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Tong Tiangen <tongtiangen@huawei.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [RFC PATCH -next V2 5/7] arm64: add get_user to machine check
 safe
Message-ID: <Yk14AwR92MX0LKqZ@FVFF77S0Q05N>
References: <20220406091311.3354723-1-tongtiangen@huawei.com>
 <20220406091311.3354723-6-tongtiangen@huawei.com>
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On Wed, Apr 06, 2022 at 09:13:09AM +0000, Tong Tiangen wrote:
> Add scenarios get_user to machine check safe. The processing of
> EX_TYPE_UACCESS_ERR_ZERO and EX_TYPE_UACCESS_ERR_ZERO_UCE_RECOVERY is same
> and both return -EFAULT.

Which uaccess cases do we expect to *not* be recoverable?

Naively I would assume that if we're going to treat a memory error on a uaccess
as fatal to userspace we should be able to do that for *any* uacesses.

The commit message should explain why we need the distinction between a
recoverable uaccess and a non-recoverable uaccess.

Thanks,
Mark.

> 
> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
> ---
>  arch/arm64/include/asm/asm-extable.h | 14 +++++++++++++-
>  arch/arm64/include/asm/uaccess.h     |  2 +-
>  arch/arm64/mm/extable.c              |  1 +
>  3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
> index 74d1db74fd86..bfc2d224cbae 100644
> --- a/arch/arm64/include/asm/asm-extable.h
> +++ b/arch/arm64/include/asm/asm-extable.h
> @@ -10,8 +10,11 @@
>  
>  /* _MC indicates that can fixup from machine check errors */
>  #define EX_TYPE_FIXUP_MC		5
> +#define EX_TYPE_UACCESS_ERR_ZERO_MC	6
>  
> -#define IS_EX_TYPE_MC(type) (type == EX_TYPE_FIXUP_MC)
> +#define IS_EX_TYPE_MC(type)			\
> +	(type == EX_TYPE_FIXUP_MC ||		\
> +	 type == EX_TYPE_UACCESS_ERR_ZERO_MC)
>  
>  #ifdef __ASSEMBLY__
>  
> @@ -77,6 +80,15 @@
>  #define EX_DATA_REG(reg, gpr)						\
>  	"((.L__gpr_num_" #gpr ") << " __stringify(EX_DATA_REG_##reg##_SHIFT) ")"
>  
> +#define _ASM_EXTABLE_UACCESS_ERR_ZERO_MC(insn, fixup, err, zero)		\
> +	__DEFINE_ASM_GPR_NUMS							\
> +	__ASM_EXTABLE_RAW(#insn, #fixup,					\
> +			  __stringify(EX_TYPE_UACCESS_ERR_ZERO_MC),		\
> +			  "("							\
> +			    EX_DATA_REG(ERR, err) " | "				\
> +			    EX_DATA_REG(ZERO, zero)				\
> +			  ")")
> +
>  #define _ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, zero)		\
>  	__DEFINE_ASM_GPR_NUMS						\
>  	__ASM_EXTABLE_RAW(#insn, #fixup, 				\
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index e8dce0cc5eaa..24b662407fbd 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -236,7 +236,7 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>  	asm volatile(							\
>  	"1:	" load "	" reg "1, [%2]\n"			\
>  	"2:\n"								\
> -	_ASM_EXTABLE_UACCESS_ERR_ZERO(1b, 2b, %w0, %w1)			\
> +	_ASM_EXTABLE_UACCESS_ERR_ZERO_MC(1b, 2b, %w0, %w1)		\
>  	: "+r" (err), "=&r" (x)						\
>  	: "r" (addr))
>  
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index f1134c88e849..7c05f8d2bce0 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -95,6 +95,7 @@ bool fixup_exception(struct pt_regs *regs, unsigned int esr)
>  	case EX_TYPE_BPF:
>  		return ex_handler_bpf(ex, regs);
>  	case EX_TYPE_UACCESS_ERR_ZERO:
> +	case EX_TYPE_UACCESS_ERR_ZERO_MC:
>  		return ex_handler_uaccess_err_zero(ex, regs);
>  	case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
>  		return ex_handler_load_unaligned_zeropad(ex, regs);
> -- 
> 2.18.0.huawei.25
> 
> 
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