Hi Mike,
Le 18/09/2023 à 09:29, Mike Rapoport a écrit :
> From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx>
>
> powerpc overrides kprobes::alloc_insn_page() to remove writable
> permissions when STRICT_MODULE_RWX is on.
>
> Add definition of EXECMEM_KRPOBES to execmem_params to allow using the
> generic kprobes::alloc_insn_page() with the desired permissions.
>
> As powerpc uses breakpoint instructions to inject kprobes, it does not
> need to constrain kprobe allocations to the modules area and can use the
> entire vmalloc address space.
I don't understand what you mean here. Does it mean kprobe allocation
doesn't need to be executable ? I don't think so based on the pgprot you
set.
On powerpc book3s/32, vmalloc space is not executable. Only modules
space is executable. X/NX cannot be set on a per page basis, it can only
be set on a 256 Mbytes segment basis.
See commit c49643319715 ("powerpc/32s: Only leave NX unset on segments
used for modules") and 6ca055322da8 ("powerpc/32s: Use dedicated segment
for modules with STRICT_KERNEL_RWX") and 7bee31ad8e2f ("powerpc/32s: Fix
is_module_segment() when MODULES_VADDR is defined").
So if your intention is still to have an executable kprobes, then you
can't use vmalloc address space.
Christophe
>
> Signed-off-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
> ---
> arch/powerpc/kernel/kprobes.c | 14 --------------
> arch/powerpc/kernel/module.c | 11 +++++++++++
> 2 files changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 62228c7072a2..14c5ddec3056 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -126,20 +126,6 @@ kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offse
> return (kprobe_opcode_t *)(addr + offset);
> }
>
> -void *alloc_insn_page(void)
> -{
> - void *page;
> -
> - page = execmem_text_alloc(EXECMEM_KPROBES, PAGE_SIZE);
> - if (!page)
> - return NULL;
> -
> - if (strict_module_rwx_enabled())
> - set_memory_rox((unsigned long)page, 1);
> -
> - return page;
> -}
> -
> int arch_prepare_kprobe(struct kprobe *p)
> {
> int ret = 0;
> diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> index 824d9541a310..bf2c62aef628 100644
> --- a/arch/powerpc/kernel/module.c
> +++ b/arch/powerpc/kernel/module.c
> @@ -95,6 +95,9 @@ static struct execmem_params execmem_params __ro_after_init = {
> [EXECMEM_DEFAULT] = {
> .alignment = 1,
> },
> + [EXECMEM_KPROBES] = {
> + .alignment = 1,
> + },
> [EXECMEM_MODULE_DATA] = {
> .alignment = 1,
> },
> @@ -135,5 +138,13 @@ struct execmem_params __init *execmem_arch_params(void)
>
> range->pgprot = prot;
>
> + execmem_params.ranges[EXECMEM_KPROBES].start = VMALLOC_START;
> + execmem_params.ranges[EXECMEM_KPROBES].start = VMALLOC_END;
> +
> + if (strict_module_rwx_enabled())
> + execmem_params.ranges[EXECMEM_KPROBES].pgprot = PAGE_KERNEL_ROX;
> + else
> + execmem_params.ranges[EXECMEM_KPROBES].pgprot = PAGE_KERNEL_EXEC;
> +
> return &execmem_params;
> }
