linux-kernel - Re: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

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Message-ID: <4a39282c-2c69-1a09-ef50-b5c8c25d0a02@c-s.fr>
Date:   Tue, 18 Apr 2017 10:15:16 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing
 unused memory



Le 18/04/2017 à 08:40, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@....fr> writes:
>
>
>> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
>> index a65c0b4c0669..d506bd61b629 100644
>> --- a/arch/powerpc/mm/pgtable_32.c
>> +++ b/arch/powerpc/mm/pgtable_32.c
>> @@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
>>          return(retval);
>>  }
>>
>> +void remap_init_ram(void)
>> +{
>> +	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
>> +	unsigned long end = (unsigned long)_einittext;
>> +	unsigned long va;
>> +
>> +	for (va = start; va < end; va += PAGE_SIZE) {
>> +		pte_t *kpte;
>> +		pmd_t *kpmd;
>> +		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
>> +
>> +		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
>> +			continue;
>> +		__set_pte_at(&init_mm, va, kpte, pte, 0);
>> +		wmb();
>> +		pte_unmap(kpte);
>> +	}
>> +	flush_tlb_kernel_range(start, end);
>> +}
>
> Can we just use unmap_kernel_range() ?

We only want to remove the X bit.
I think unmap_kernel_range() will unmap the area, wheareas we want to 
keep it as part of the linear data area.

Christophe

>
> Is this sufficient on all 32-bit PPC? (I have no idea)
>
> cheers
>