Re: [PATCH v3 2/4] powerpc/kprobes: Mark newly allocated probes as RO

[Andrew Donnellan <ajd@linux.ibm.com>]

On 4/10/19 5:50 pm, Russell Currey wrote:
> With CONFIG_STRICT_KERNEL_RWX=y and CONFIG_KPROBES=y, there will be one
> W+X page at boot by default.  This can be tested with
> CONFIG_PPC_PTDUMP=y and CONFIG_PPC_DEBUG_WX=y set, and checking the
> kernel log during boot.
> 
> powerpc doesn't implement its own alloc() for kprobes like other
> architectures do, but we couldn't immediately mark RO anyway since we do
> a memcpy to the page we allocate later.  After that, nothing should be
> allowed to modify the page, and write permissions are removed well
> before the kprobe is armed.
> 
> Signed-off-by: Russell Currey <ruscur@russell.cc>

Commit message nit: if there's an important detail in the summary line, 
repeat that in the body of the commit message, those two paragraphs 
don't tell you what the commit actually _does_, that's in the summary line

> ---
>   arch/powerpc/kernel/kprobes.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 2d27ec4feee4..2610496de7c7 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -24,6 +24,7 @@
>   #include <asm/sstep.h>
>   #include <asm/sections.h>
>   #include <linux/uaccess.h>
> +#include <linux/set_memory.h>
>   
>   DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
>   DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> @@ -131,6 +132,8 @@ int arch_prepare_kprobe(struct kprobe *p)
>   			(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
>   	}
>   
> +	set_memory_ro((unsigned long)p->ainsn.insn, 1);
> +
>   	p->ainsn.boostable = 0;
>   	return ret;
>   }
> 

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited