Subject: Re: [PATCH v3] powerpc: Fix PTE page address mismatch in pgtable ctor/dtor

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 09 Dec 2013 14:12:26 +0530

"Hong H. Pham" <[email-masked]> writes:

> From: "Hong H. Pham" <[email-masked]>
>
> In pte_alloc_one(), pgtable_page_ctor() is passed an address that has
> not been converted by page_address() to the newly allocated PTE page.
>
> When the PTE is freed, __pte_free_tlb() calls pgtable_page_dtor()
> with an address to the PTE page that has been converted by page_address().
> The mismatch in the PTE's page address causes pgtable_page_dtor() to access
> invalid memory, so resources for that PTE (such as the page lock) is not
> properly cleaned up.
>
> On PPC32, only SMP kernels are affected.
>
> On PPC64, only SMP kernels with 4K page size are affected.
>
> This bug was introduced by commit d614bb041209fd7cb5e4b35e11a7b2f6ee8f62b8
> "powerpc: Move the pte free routines from common header".
>
> On a preempt-rt kernel, a spinlock is dynamically allocated for each
> PTE in pgtable_page_ctor().  When the PTE is freed, calling
> pgtable_page_dtor() with a mismatched page address causes a memory leak,
> as the pointer to the PTE's spinlock is bogus.
>
> On mainline, there isn't any immediately obvious symptoms, but the
> problem still exists here.
>
> Fixes: d614bb041209fd7c "powerpc: Move the pte free routes from common header"
> Cc: Paul Mackerras <[email-masked]>
> Cc: Aneesh Kumar K.V <[email-masked]>
> Cc: Benjamin Herrenschmidt <[email-masked]>
> Cc: linux-stable <[email-masked]> # v3.10+
> Signed-off-by: Hong H. Pham <[email-masked]>

Reviewed-by: Aneesh Kumar K.V <[email-masked]>

> ---
>  arch/powerpc/include/asm/pgalloc-32.h | 6 ++----
>  arch/powerpc/include/asm/pgalloc-64.h | 6 ++----
>  2 files changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/pgalloc-32.h b/arch/powerpc/include/asm/pgalloc-32.h
> index 27b2386..842846c 100644
> --- a/arch/powerpc/include/asm/pgalloc-32.h
> +++ b/arch/powerpc/include/asm/pgalloc-32.h
> @@ -84,10 +84,8 @@ static inline void pgtable_free_tlb(struct mmu_gather *tlb,
>  static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t table,
>  				  unsigned long address)
>  {
> -	struct page *page = page_address(table);
> -
>  	tlb_flush_pgtable(tlb, address);
> -	pgtable_page_dtor(page);
> -	pgtable_free_tlb(tlb, page, 0);
> +	pgtable_page_dtor(table);
> +	pgtable_free_tlb(tlb, page_address(table), 0);
>  }
>  #endif /* _ASM_POWERPC_PGALLOC_32_H */
> diff --git a/arch/powerpc/include/asm/pgalloc-64.h b/arch/powerpc/include/asm/pgalloc-64.h
> index f65e27b..256d6f8 100644
> --- a/arch/powerpc/include/asm/pgalloc-64.h
> +++ b/arch/powerpc/include/asm/pgalloc-64.h
> @@ -144,11 +144,9 @@ static inline void pgtable_free_tlb(struct mmu_gather *tlb,
>  static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t table,
>  				  unsigned long address)
>  {
> -	struct page *page = page_address(table);
> -
>  	tlb_flush_pgtable(tlb, address);
> -	pgtable_page_dtor(page);
> -	pgtable_free_tlb(tlb, page, 0);
> +	pgtable_page_dtor(table);
> +	pgtable_free_tlb(tlb, page_address(table), 0);
>  }
>
>  #else /* if CONFIG_PPC_64K_PAGES */
> -- 
> 1.8.3.2