linux-kernel - Re: [PATCH v3 06/21] arm64: pgtable: implement static [pte|pmd|pud]

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Message-ID: <20160111162449.GP6499@leverpostej>
Date:	Mon, 11 Jan 2016 16:24:49 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	kernel-hardening@...ts.openwall.com, will.deacon@....com,
	catalin.marinas@....com, leif.lindholm@...aro.org,
	keescook@...omium.org, linux-kernel@...r.kernel.org,
	stuart.yoder@...escale.com, bhupesh.sharma@...escale.com,
	arnd@...db.de, marc.zyngier@....com, christoffer.dall@...aro.org
Subject: Re: [PATCH v3 06/21] arm64: pgtable: implement static
 [pte|pmd|pud]_offset variants

On Mon, Jan 11, 2016 at 02:18:59PM +0100, Ard Biesheuvel wrote:
> The page table accessors pte_offset(), pud_offset() and pmd_offset()
> rely on __va translations, so they can only be used after the linear
> mapping has been installed. For the early fixmap and kasan init routines,
> whose page tables are allocated statically in the kernel image, these
> functions will return bogus values. So implement pmd_offset_kimg() and
> pud_offset_kimg(), which can be used instead before any page tables have
> been allocated dynamically.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

This looks good to me. One possible suggsetion below, but either way:

Reviewed-by: Mark Rutland <mark.rutland@....com>

> ---
>  arch/arm64/include/asm/pgtable.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 6129f6755081..7b4e16068c9f 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -449,6 +449,9 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>  
>  #define pmd_page(pmd)		pfn_to_page(__phys_to_pfn(pmd_val(pmd) & PHYS_MASK))
>  
> +/* use ONLY for statically allocated translation tables */
> +#define pte_offset_kimg(dir,addr)	((pte_t *)__phys_to_kimg(pte_offset_phys((dir), (addr))))
> +

Given that we're probably only going to use this during one-off setup,
maybe it's worth something like:

#define IN_KERNEL_IMAGE(p) ({						\
	unsigned long __p = (unsigned long)p;				\
	KIMAGE_VADDR <= __p && __p < _end;				\
})

#define pte_offset_kimg(dir,addr) ({					\
	BUG_ON(!IN_KERNEL_IMAGE(dir));					\
	((pte_t *)__phys_to_kimg(pte_offset_phys((dir), (addr))));	\
})

That might be overkill, though, given all it does is turn one runtime
failure into another runtime failure.

Mark.

>  /*
>   * Conversion functions: convert a page and protection to a page entry,
>   * and a page entry and page directory to the page they refer to.
> @@ -492,6 +495,9 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>  
>  #define pud_page(pud)		pfn_to_page(__phys_to_pfn(pud_val(pud) & PHYS_MASK))
>  
> +/* use ONLY for statically allocated translation tables */
> +#define pmd_offset_kimg(dir,addr)	((pmd_t *)__phys_to_kimg(pmd_offset_phys((dir), (addr))))
> +
>  #else
>  
>  #define pud_page_paddr(pud)	({ BUILD_BUG(); 0; })
> @@ -502,6 +508,8 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>  #define pmd_set_fixmap_offset(pudp, addr)	((pmd_t *)pudp)
>  #define pmd_clear_fixmap()
>  
> +#define pmd_offset_kimg(dir,addr)	((pmd_t *)dir)
> +
>  #endif	/* CONFIG_PGTABLE_LEVELS > 2 */
>  
>  #if CONFIG_PGTABLE_LEVELS > 3
> @@ -540,6 +548,9 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>  
>  #define pgd_page(pgd)		pfn_to_page(__phys_to_pfn(pgd_val(pgd) & PHYS_MASK))
>  
> +/* use ONLY for statically allocated translation tables */
> +#define pud_offset_kimg(dir,addr)	((pud_t *)__phys_to_kimg(pud_offset_phys((dir), (addr))))
> +
>  #else
>  
>  #define pgd_page_paddr(pgd)	({ BUILD_BUG(); 0;})
> @@ -550,6 +561,8 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>  #define pud_set_fixmap_offset(pgdp, addr)	((pud_t *)pgdp)
>  #define pud_clear_fixmap()
>  
> +#define pud_offset_kimg(dir,addr)	((pud_t *)dir)
> +
>  #endif  /* CONFIG_PGTABLE_LEVELS > 3 */
>  
>  #define pgd_ERROR(pgd)		__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
> -- 
> 2.5.0
>