[PATCH v10 05/10] powerpc/bpf: Write protect JIT code

[Michael Ellerman]

Jordan Niethe <jniethe5 at gmail.com> writes:

> Once CONFIG_STRICT_MODULE_RWX is enabled there will be no need to
> override bpf_jit_free() because it is now possible to set images
> read-only. So use the default implementation.
>
> Also add the necessary call to bpf_jit_binary_lock_ro() which will
> remove write protection and add exec protection to the JIT image after
> it has finished being written.
>
> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> ---
> v10: New to series
> ---
>  arch/powerpc/net/bpf_jit_comp.c   | 5 ++++-
>  arch/powerpc/net/bpf_jit_comp64.c | 4 ++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index e809cb5a1631..8015e4a7d2d4 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -659,12 +659,15 @@ void bpf_jit_compile(struct bpf_prog *fp)
>  		bpf_jit_dump(flen, proglen, pass, code_base);
>  
>  	bpf_flush_icache(code_base, code_base + (proglen/4));
> -
>  #ifdef CONFIG_PPC64
>  	/* Function descriptor nastiness: Address + TOC */
>  	((u64 *)image)[0] = (u64)code_base;
>  	((u64 *)image)[1] = local_paca->kernel_toc;
>  #endif
> +	if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {
> +		set_memory_ro((unsigned long)image, alloclen >> PAGE_SHIFT);
> +		set_memory_x((unsigned long)image, alloclen >> PAGE_SHIFT);
> +	}

You don't need to check the ifdef in a caller, there are stubs that
compile to nothing when CONFIG_ARCH_HAS_SET_MEMORY=n.

> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index aaf1a887f653..1484ad588685 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -1240,6 +1240,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>  	fp->jited_len = alloclen;
>  
>  	bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
> +	if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
> +		bpf_jit_binary_lock_ro(bpf_hdr);

Do we need the ifdef here either? Looks like it should be safe to call
due to the stubs.

> @@ -1262,6 +1264,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>  }
>  
>  /* Overriding bpf_jit_free() as we don't set images read-only. */
> +#ifndef CONFIG_STRICT_MODULE_RWX

Did you test without this and notice something broken?

Looking at the generic version I can't tell why we need to override
this. Maybe we don't (anymore?) ?

cheers

>  void bpf_jit_free(struct bpf_prog *fp)
>  {
>  	unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
> @@ -1272,3 +1275,4 @@ void bpf_jit_free(struct bpf_prog *fp)
>  
>  	bpf_prog_unlock_free(fp);
>  }
> +#endif
> -- 
> 2.25.1