Re: [PATCH v12 3/8] powerpc/kprobes: Mark newly allocated probes as ROX

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 06/05/2021 à 04:34, Jordan Niethe a écrit :
> From: Russell Currey <ruscur@russell.cc>
> 
> Add the arch specific insn page allocator for powerpc. This allocates
> ROX pages if STRICT_KERNEL_RWX is enabled. These pages are only written
> to with patch_instruction() which is able to write RO pages.
> 
> Reviewed-by: Daniel Axtens <dja@axtens.net>
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> [jpn: Reword commit message, switch to __vmalloc_node_range()]
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
> v9: - vmalloc_exec() no longer exists
>      - Set the page to RW before freeing it
> v10: - use __vmalloc_node_range()
> v11: - Neaten up
> v12: - Switch from __vmalloc_node_range() to module_alloc()
> ---
>   arch/powerpc/kernel/kprobes.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 01ab2163659e..73a294802f72 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -19,11 +19,13 @@
>   #include <linux/extable.h>
>   #include <linux/kdebug.h>
>   #include <linux/slab.h>
> +#include <linux/moduleloader.h>
>   #include <asm/code-patching.h>
>   #include <asm/cacheflush.h>
>   #include <asm/sstep.h>
>   #include <asm/sections.h>
>   #include <asm/inst.h>
> +#include <asm/set_memory.h>
>   #include <linux/uaccess.h>
>   
>   DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> @@ -103,6 +105,21 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
>   	return addr;
>   }
>   
> +void *alloc_insn_page(void)
> +{
> +	void *page;
> +
> +	page = module_alloc(PAGE_SIZE);
> +	if (!page)
> +		return NULL;
> +
> +	if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {

I'm not sure this test is OK, because strict kernel/module rwx can be disabled at boottime.
There is a global variable 'rodata_enabled' to reflect that.

We have a helper in powerpc asm/mmu.h called strict_kernel_rwx_enabled() to check it.


> +		set_memory_ro((unsigned long)page, 1);
> +		set_memory_x((unsigned long)page, 1);
> +	}
> +	return page;
> +}
> +
>   int arch_prepare_kprobe(struct kprobe *p)
>   {
>   	int ret = 0;
>