On Wed, Apr 30, 2025 at 8:04 AM Alexei Starovoitov
<alexei.starovoi...@gmail.com> wrote:
>
> On Mon, Apr 28, 2025 at 9:13 PM Pingfan Liu <pi...@redhat.com> wrote:
> +__bpf_kfunc struct mem_range_result *bpf_kexec_decompress(char
> *image_gz_payload, int image_gz_sz,
> > + unsigned int expected_decompressed_sz)
> > +{
> > + decompress_fn decompressor;
> > + //todo, use flush to cap the memory size used by decompression
> > + long (*flush)(void*, unsigned long) = NULL;
> > + struct mem_range_result *range;
> > + const char *name;
> > + void *output_buf;
> > + char *input_buf;
> > + int ret;
> > +
> > + range = kmalloc(sizeof(struct mem_range_result), GFP_KERNEL);
> > + if (!range) {
> > + pr_err("fail to allocate mem_range_result\n");
> > + return NULL;
> > + }
> > + refcount_set(&range->usage, 1);
> > +
> > + input_buf = vmalloc(image_gz_sz);
> > + if (!input_buf) {
> > + pr_err("fail to allocate input buffer\n");
> > + kfree(range);
> > + return NULL;
> > + }
> > +
> > + ret = copy_from_kernel_nofault(input_buf, image_gz_payload,
> > image_gz_sz);
> > + if (ret < 0) {
> > + pr_err("Error when copying from 0x%px, size:0x%x\n",
> > + image_gz_payload, image_gz_sz);
> > + kfree(range);
> > + vfree(input_buf);
> > + return NULL;
> > + }
> > +
> > + output_buf = vmalloc(expected_decompressed_sz);
> > + if (!output_buf) {
> > + pr_err("fail to allocate output buffer\n");
> > + kfree(range);
> > + vfree(input_buf);
> > + return NULL;
> > + }
> > +
> > + decompressor = decompress_method(input_buf, image_gz_sz, &name);
> > + if (!decompressor) {
> > + pr_err("Can not find decompress method\n");
> > + kfree(range);
> > + vfree(input_buf);
> > + vfree(output_buf);
> > + return NULL;
> > + }
> > + //to do, use flush
> > + ret = decompressor(image_gz_payload, image_gz_sz, NULL, NULL,
> > + output_buf, NULL, NULL);
> > +
> > + /* Update the range map */
> > + if (ret == 0) {
> > + range->buf = output_buf;
> > + range->size = expected_decompressed_sz;
> > + range->status = 0;
> > + } else {
> > + pr_err("Decompress error\n");
> > + vfree(output_buf);
> > + kfree(range);
> > + return NULL;
> > + }
> > + pr_info("%s, return range 0x%lx\n", __func__, range);
> > + return range;
> > +}
>
> These kfuncs look like generic decompress routines.
> They're not related to kexec and probably should be in kernel/bpf/helpers.c
> or kernel/bpf/compression.c instead of kernel/kexec_pe_image.c.
>
Thanks for your suggestion. I originally considered using these kfuncs
only in kexec context (Later, introducing a dedicated BPF_PROG_TYPE
for kexec). They are placed under a lock so that a malice attack can
not exhaust the memory through repeatedly calling to the decompress
kfunc.
To generalize these kfunc, I think I can add some boundary control of
the memory usage to prevent such attacks.
> They also must be KF_SLEEPABLE.
> Please test your patches with all kernel debugs enabled.
> Otherwise you would have seen all these "sleeping while atomic"
> issues yourself.
>
See, I will have all these debug options for the V3 test.
Appreciate your insight.
Regards,
Pingfan
