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Date: Mon, 20 Jan 2020 09:35:04 +0100
From: Christophe Leroy <christophe.leroy@....fr>
To: Russell Currey <ruscur@...sell.cc>, linuxppc-dev@...ts.ozlabs.org
Cc: joel@....id.au, mpe@...erman.id.au, ajd@...ux.ibm.com, dja@...ens.net,
 npiggin@...il.com, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v6 1/5] powerpc/mm: Implement set_memory() routines



Le 24/12/2019 à 06:55, Russell Currey a écrit :
> The set_memory_{ro/rw/nx/x}() functions are required for STRICT_MODULE_RWX,
> and are generally useful primitives to have.  This implementation is
> designed to be completely generic across powerpc's many MMUs.
> 
> It's possible that this could be optimised to be faster for specific
> MMUs, but the focus is on having a generic and safe implementation for
> now.
> 
> This implementation does not handle cases where the caller is attempting
> to change the mapping of the page it is executing from, or if another
> CPU is concurrently using the page being altered.  These cases likely
> shouldn't happen, but a more complex implementation with MMU-specific code
> could safely handle them, so that is left as a TODO for now.
> 
> Signed-off-by: Russell Currey <ruscur@...sell.cc>
> ---
>   arch/powerpc/Kconfig                  |  1 +
>   arch/powerpc/include/asm/set_memory.h | 32 +++++++++++
>   arch/powerpc/mm/Makefile              |  1 +
>   arch/powerpc/mm/pageattr.c            | 83 +++++++++++++++++++++++++++
>   4 files changed, 117 insertions(+)
>   create mode 100644 arch/powerpc/include/asm/set_memory.h
>   create mode 100644 arch/powerpc/mm/pageattr.c
> 
> +static int __change_page_attr(pte_t *ptep, unsigned long addr, void *data)
> +{
> +	int action = *((int *)data);
> +	pte_t pte_val;

pte_val is really not a good naming, because pte_val() is already a 
function which returns the value of a pte_t var.

Here you should name it 'pte' as usual.

Christophe

> +
> +	// invalidate the PTE so it's safe to modify
> +	pte_val = ptep_get_and_clear(&init_mm, addr, ptep);
> +	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> +
> +	// modify the PTE bits as desired, then apply
> +	switch (action) {
> +	case SET_MEMORY_RO:
> +		pte_val = pte_wrprotect(pte_val);
> +		break;
> +	case SET_MEMORY_RW:
> +		pte_val = pte_mkwrite(pte_val);
> +		break;
> +	case SET_MEMORY_NX:
> +		pte_val = pte_exprotect(pte_val);
> +		break;
> +	case SET_MEMORY_X:
> +		pte_val = pte_mkexec(pte_val);
> +		break;
> +	default:
> +		WARN_ON(true);
> +		return -EINVAL;
> +	}
> +
> +	set_pte_at(&init_mm, addr, ptep, pte_val);
> +
> +	return 0;
> +}
> +

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