[PATCH v1 1/8] powerpc/lib/code-patching: Enhance code patching

[christophe leroy]

Le 25/05/2017 à 05:36, Balbir Singh a écrit :
> Today our patching happens via direct copy and
> patch_instruction. The patching code is well
> contained in the sense that copying bits are limited.
>
> While considering implementation of CONFIG_STRICT_RWX,
> the first requirement is to a create another mapping
> that will allow for patching. We create the window using
> text_poke_area, allocated via get_vm_area(), which might
> be an overkill. We can do per-cpu stuff as well. The
> downside of these patches that patch_instruction is
> now synchornized using a lock. Other arches do similar
> things, but use fixmaps. The reason for not using
> fixmaps is to make use of any randomization in the
> future. The code also relies on set_pte_at and pte_clear
> to do the appropriate tlb flushing.
>
> Signed-off-by: Balbir Singh <bsingharora at gmail.com>
> ---
>  arch/powerpc/lib/code-patching.c | 88 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 84 insertions(+), 4 deletions(-)
>

[...]

> +static int kernel_map_addr(void *addr)
> +{
> +	unsigned long pfn;
>  	int err;
>
> -	__put_user_size(instr, addr, 4, err);
> +	if (is_vmalloc_addr(addr))
> +		pfn = vmalloc_to_pfn(addr);
> +	else
> +		pfn = __pa_symbol(addr) >> PAGE_SHIFT;
> +
> +	err = map_kernel_page((unsigned long)text_poke_area->addr,
> +			(pfn << PAGE_SHIFT), _PAGE_KERNEL_RW | _PAGE_PRESENT);



Why not use PAGE_KERNEL instead of _PAGE_KERNEL_RW | _PAGE_PRESENT ?

 From asm/pte-common.h :

#define PAGE_KERNEL	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
#define _PAGE_BASE	(_PAGE_BASE_NC)
#define _PAGE_BASE_NC	(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_PSIZE)

Also, in pte-common.h, maybe the following defines could/should be 
reworked once you serie applied, shouldn't it ?

/* Protection used for kernel text. We want the debuggers to be able to
  * set breakpoints anywhere, so don't write protect the kernel text
  * on platforms where such control is possible.
  */
#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || 
defined(CONFIG_BDI_SWITCH) ||\
	defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE)
#define PAGE_KERNEL_TEXT	PAGE_KERNEL_X
#else
#define PAGE_KERNEL_TEXT	PAGE_KERNEL_ROX
#endif


Christophe

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