[PATCH v9 3/8] powerpc/kprobes: Mark newly allocated probes as RO

[Christophe Leroy]

Le 16/03/2021 à 04:17, Jordan Niethe a écrit :
> From: Russell Currey <ruscur at russell.cc>
> 
> 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.
> 

This text is confusing. I don't understand what is the status before the patch, and what is the 
status after.

"there will be one ...", does it mean after the patch ?

> Add an arch specific insn page allocator which returns RO pages if
> STRICT_KERNEL_RWX is enabled. This page is only written to with
> patch_instruction() which is able to write RO pages.

"an" or "the" arch specific insn page allocator ?

> 
> Reviewed-by: Daniel Axtens <dja at axtens.net>
> Signed-off-by: Russell Currey <ruscur at russell.cc>
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> [jpn: Reword commit message, switch from vmalloc_exec(), add
>        free_insn_page()]
> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> ---
> v9: - vmalloc_exec() no longer exists
>      - Set the page to RW before freeing it
> ---
>   arch/powerpc/kernel/kprobes.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 01ab2163659e..bb7e4d321988 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -25,6 +25,8 @@
>   #include <asm/sections.h>
>   #include <asm/inst.h>
>   #include <linux/uaccess.h>
> +#include <linux/set_memory.h>
> +#include <linux/vmalloc.h>
>   
>   DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
>   DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> @@ -103,6 +105,26 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
>   	return addr;
>   }
>   
> +void *alloc_insn_page(void)
> +{
> +	void *page = vmalloc(PAGE_SIZE);

Can't do that on book3s/32, see https://github.com/linuxppc/linux/commit/6ca05532 and 
https://github.com/linuxppc/linux/commit/7fbc22ce

Should do:
	return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END, GFP_KERNEL,
				    PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
				    __builtin_return_address(0));


To keep it simple, you'll probably need to define MODULES_VADDR and MODULES_END as resp 
VMALLOC_START and VMALLOC_END when they are not defined, maybe in asm/pgtable.h

> +
> +	if (!page)
> +		return NULL;
> +
> +	set_memory_ro((unsigned long)page, 1);
> +	set_memory_x((unsigned long)page, 1);
> +
> +	return page;
> +}
> +
> +void free_insn_page(void *page)
> +{
> +	set_memory_nx((unsigned long)page, 1);
> +	set_memory_rw((unsigned long)page, 1);
> +	vfree(page);
> +}
> +
>   int arch_prepare_kprobe(struct kprobe *p)
>   {
>   	int ret = 0;
>