[RFC PATCH 2/3] powerpc/bpf: implement bpf_arch_text_invalidate for bpf_prog_pack

[Christophe Leroy]

Le 10/11/2022 à 19:43, Hari Bathini a écrit :
> Implement bpf_arch_text_invalidate and use it to fill unused part of
> the bpf_prog_pack with trap instructions when a BPF program is freed.

Same here, allthough patch_instruction() is nice for a first try, it is 
not the solution on the long run. Same as with previous patch, it should 
just map the necessary page by allocating a vma area then mapping the 
associated physical pages over it using map_kernel_page(), then use 
bpf_jit_fill_ill_insns() over than page.

> 
> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 7383e0effad2..f925755cd249 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -26,6 +26,33 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
>   	memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
>   }
>   
> +/*
> + * Patch 'len' bytes with trap instruction at addr, one instruction
> + * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
> + */
> +static void *bpf_patch_ill_insns(void *addr, size_t len)
> +{
> +	void *ret = ERR_PTR(-EINVAL);
> +	size_t patched = 0;
> +	u32 *start = addr;
> +
> +	if (WARN_ON_ONCE(core_kernel_text((unsigned long)addr)))
> +		return ret;
> +
> +	mutex_lock(&text_mutex);
> +	while (patched < len) {
> +		if (patch_instruction(start++, ppc_inst(PPC_RAW_TRAP())))

Use BREAKPOINT_INSTRUCTION instead of PPC_RAW_TRAP()

> +			goto error;
> +
> +		patched += 4;
> +	}
> +
> +	ret = addr;
> +error:
> +	mutex_unlock(&text_mutex);
> +	return ret;
> +}
> +
>   /*
>    * Patch 'len' bytes of instructions from opcode to addr, one instruction
>    * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
> @@ -394,3 +421,8 @@ void *bpf_arch_text_copy(void *dst, void *src, size_t len)
>   {
>   	return bpf_patch_instructions(dst, src, len);
>   }
> +
> +int bpf_arch_text_invalidate(void *dst, size_t len)
> +{
> +	return IS_ERR(bpf_patch_ill_insns(dst, len));
> +}


The exact same split between bpf_arch_text_invalidate() and 
bpf_patch_ill_insns() as previous patch could be done here.