linux-kernel - Re: [PATCH] arm64: mm: check virtual addr in virt_to_page() if CONFIG_DEBUG

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Date:   Tue, 16 Apr 2019 12:30:58 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Miles Chen <miles.chen@...iatek.com>
Cc:     Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] arm64: mm: check virtual addr in virt_to_page() if
 CONFIG_DEBUG_VIRTUAL=y

On Tue, Apr 16, 2019 at 01:36:36AM +0800, Miles Chen wrote:
> This change uses the original virt_to_page() (the one with __pa()) to
> check the given virtual address if CONFIG_DEBUG_VIRTUAL=y.
> 
> Recently, I worked on a bug: a driver passes a symbol address to
> dma_map_single() and the virt_to_page() (called by dma_map_single())
> does not work for non-linear addresses after commit 9f2875912dac
> ("arm64: mm: restrict virt_to_page() to the linear mapping").
> 
> I tried to trap the bug by enabling CONFIG_DEBUG_VIRTUAL but it
> did not work - bacause the commit removes the __pa() from
> virt_to_page() but CONFIG_DEBUG_VIRTUAL checks the virtual address
> in __pa()/__virt_to_phys().
> 
> A simple solution is to use the original virt_to_page()
> (the one with__pa()) if CONFIG_DEBUG_VIRTUAL=y.
> 
> Signed-off-by: Miles Chen <miles.chen@...iatek.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  arch/arm64/include/asm/memory.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 290195168bb3..2cb8248fa2c8 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -302,7 +302,7 @@ static inline void *phys_to_virt(phys_addr_t x)
>   */
>  #define ARCH_PFN_OFFSET		((unsigned long)PHYS_PFN_OFFSET)
>  
> -#ifndef CONFIG_SPARSEMEM_VMEMMAP
> +#if !defined(CONFIG_SPARSEMEM_VMEMMAP) || defined(CONFIG_DEBUG_VIRTUAL)
>  #define virt_to_page(kaddr)	pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
>  #define _virt_addr_valid(kaddr)	pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
>  #else

IIUC, this shouldn't change the behaviour of virt_addr_valid(). The
patch looks fine to me.

Acked-by: Catalin Marinas <catalin.marinas@....com>