Re: [PATCHv5 06/12] kexec: Integrate with the introduced bpf kfuncs

[Philipp Rudo <prudo@redhat.com>]

Hi Pingfan,

On Tue, 16 Sep 2025 14:52:38 +0800
Pingfan Liu <piliu@redhat.com> wrote:

> On Mon, Sep 01, 2025 at 04:30:42PM +0200, Philipp Rudo wrote:
> > Hi Pingfan,
> > 
> > 
> > On Tue, 19 Aug 2025 09:24:22 +0800
> > Pingfan Liu <piliu@redhat.com> wrote:
> >   
> > > This patch does two things:
> > > First, register as a listener on bpf_copy_to_kernel()
> > > Second, in order that the hooked bpf-prog can call the sleepable kfuncs,
> > > bpf_handle_pefile and bpf_post_handle_pefile are marked as
> > > KF_SLEEPABLE.
> > > 
> > > Signed-off-by: Pingfan Liu <piliu@redhat.com>
> > > Cc: Alexei Starovoitov <ast@kernel.org>
> > > Cc: Philipp Rudo <prudo@redhat.com>
> > > Cc: Baoquan He <bhe@redhat.com>
> > > Cc: Dave Young <dyoung@redhat.com>
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: bpf@vger.kernel.org
> > > To: kexec@lists.infradead.org
> > > ---
> > >  kernel/kexec_pe_image.c | 67 +++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 67 insertions(+)
> > > 
> > > diff --git a/kernel/kexec_pe_image.c b/kernel/kexec_pe_image.c
> > > index b0cf9942e68d2..f8debcde6b516 100644
> > > --- a/kernel/kexec_pe_image.c
> > > +++ b/kernel/kexec_pe_image.c
> > > @@ -38,6 +38,51 @@ static struct kexec_res parsed_resource[3] = {
> > >  	{ KEXEC_RES_CMDLINE_NAME, },
> > >  };
> > >  
> > > +/*
> > > + * @name should be one of : kernel, initrd, cmdline
> > > + */
> > > +static int bpf_kexec_carrier(const char *name, struct mem_range_result *r)
> > > +{
> > > +	struct kexec_res *res;
> > > +	int i;
> > > +
> > > +	if (!r || !name)
> > > +		return -EINVAL;
> > > +
> > > +	for (i = 0; i < 3; i++) {
> > > +		if (!strcmp(parsed_resource[i].name, name))
> > > +			break;
> > > +	}
> > > +	if (i >= 3)
> > > +		return -EINVAL;  
> > 
> > Can you please replace the magic '3' by ARRAY_SIZE, just like you did
> > below when (un-)registering the listener.
> >   
> 
> Yes, I will introduce a macro KEXEC_RES_ARRAY_SIZE to unify all of them.

Why do you want to introduce a new macro? Why not simply use
ARRAY_SIZE(parsed_resource)?

Thanks
Philipp

> Thanks,
> 
> Pingfan
> 
> > Thanks
> > Philipp
> >   
> > > +
> > > +	res = &parsed_resource[i];
> > > +	/*
> > > +	 * Replace the intermediate resource generated by the previous step.
> > > +	 */
> > > +	if (!!res->r)
> > > +		mem_range_result_put(res->r);
> > > +	mem_range_result_get(r);
> > > +	res->r = r;
> > > +	return 0;
> > > +}
> > > +
> > > +static struct carrier_listener kexec_res_listener[3] = {
> > > +	{ .name = KEXEC_RES_KERNEL_NAME,
> > > +	  .alloc_type = 1,
> > > +	  .handler = bpf_kexec_carrier,
> > > +	},
> > > +	{ .name = KEXEC_RES_INITRD_NAME,
> > > +	  .alloc_type = 1,
> > > +	  .handler = bpf_kexec_carrier,
> > > +	},
> > > +	{ .name = KEXEC_RES_CMDLINE_NAME,
> > > +	  /* kmalloc-ed */
> > > +	  .alloc_type = 0,
> > > +	  .handler = bpf_kexec_carrier,
> > > +	},
> > > +};
> > > +
> > >  static bool pe_has_bpf_section(const char *file_buf, unsigned long pe_sz);
> > >  
> > >  static bool is_valid_pe(const char *kernel_buf, unsigned long kernel_len)
> > > @@ -159,6 +204,22 @@ __attribute__((used, optimize("O0"))) void bpf_post_handle_pefile(struct kexec_c
> > >  	dummy += 2;
> > >  }
> > >  
> > > +BTF_KFUNCS_START(kexec_modify_return_ids)
> > > +BTF_ID_FLAGS(func, bpf_handle_pefile, KF_SLEEPABLE)
> > > +BTF_ID_FLAGS(func, bpf_post_handle_pefile, KF_SLEEPABLE)
> > > +BTF_KFUNCS_END(kexec_modify_return_ids)
> > > +
> > > +static const struct btf_kfunc_id_set kexec_modify_return_set = {
> > > +	.owner = THIS_MODULE,
> > > +	.set = &kexec_modify_return_ids,
> > > +};
> > > +
> > > +static int __init kexec_bpf_prog_run_init(void)
> > > +{
> > > +	return register_btf_fmodret_id_set(&kexec_modify_return_set);
> > > +}
> > > +late_initcall(kexec_bpf_prog_run_init);
> > > +
> > >  /*
> > >   * PE file may be nested and should be unfold one by one.
> > >   * Query 'kernel', 'initrd', 'cmdline' in cur_phase, as they are inputs for the
> > > @@ -213,6 +274,9 @@ static void *pe_image_load(struct kimage *image,
> > >  	cmdline_start = cmdline;
> > >  	cmdline_sz = cmdline_len;
> > >  
> > > +	for (int i = 0; i < ARRAY_SIZE(kexec_res_listener); i++)
> > > +		register_carrier_listener(&kexec_res_listener[i]);
> > > +
> > >  	while (is_valid_format(linux_start, linux_sz) &&
> > >  	       pe_has_bpf_section(linux_start, linux_sz)) {
> > >  		struct kexec_context context;
> > > @@ -250,6 +314,9 @@ static void *pe_image_load(struct kimage *image,
> > >  		disarm_bpf_prog();
> > >  	}
> > >  
> > > +	for (int i = 0; i < ARRAY_SIZE(kexec_res_listener); i++)
> > > +		unregister_carrier_listener(kexec_res_listener[i].name);
> > > +
> > >  	/*
> > >  	 * image's kernel_buf, initrd_buf, cmdline_buf are set. Now they should
> > >  	 * be updated to the new content.  
> >   
>