linux-kernel - Re: [PATCH v2 3/3] riscv: Fix crash when flushing executable ioremap regions

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Date:   Sun, 16 Feb 2020 09:41:11 -0500
From:   Alex Ghiti <alex@...ti.fr>
To:     Jan Kiszka <jan.kiszka@....de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] riscv: Fix crash when flushing executable ioremap
 regions

Hi Jan,

On 2/15/20 6:49 AM, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@...mens.com>
> 
> Those are not backed by page structs, and pte_page is returning an
> invalid pointer.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> =2D--
>   arch/riscv/mm/cacheflush.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 8930ab7278e6..9ee2c1a387cc 100644
> =2D-- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -84,7 +84,8 @@ void flush_icache_pte(pte_t pte)
>   {
>   	struct page *page =3D pte_page(pte);
> 
> -	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
> +	if (!pfn_valid(pte_pfn(pte)) ||
> +	    !test_and_set_bit(PG_dcache_clean, &page->flags))
>   		flush_icache_all();
>   }
>   #endif /* CONFIG_MMU */
> =2D-
> 2.16.4
> 
> 

When did you encounter such a situation ? i.e. executable code that is 
not backed by struct page ?

Riscv uses the generic implementation of ioremap and the way 
_PAGE_IOREMAP is defined does not allow to map executable memory region 
using ioremap, so I'm interested to understand how we end up in 
flush_icache_pte for an executable region not backed by any struct page.

Thanks,

Alex