Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support

[Mimi Zohar]

On Tue, 2018-04-24 at 17:09 +0200, Hans de Goede wrote:
> Hi,
> 
> On 23-04-18 23:11, Luis R. Rodriguez wrote:
> > Hans, please see use of READING_FIRMWARE_PREALLOC_BUFFER, we'll need a new ID
> > and security for this type of request so IMA can reject it if the policy is
> > configured for it.
> 
> Hmm, interesting, actually it seems like the whole existence
> of READING_FIRMWARE_PREALLOC_BUFFER is a mistake, the IMA
> framework really does not care if we are loading the firmware
> into memory allocated by the firmware-loader code, or into
> memory allocated by the device-driver requesting the firmware.
> 
> As such the current IMA code (from v4.17-rc2) actually does
> not handle READING_FIRMWARE_PREALLOC_BUFFER at all, 

Right, it doesn't yet address READING_FIRMWARE_PREALLOC_BUFFER, but
should.

Depending on whether the device requesting the firmware has access to
the DMA memory, before the signature verification, will determine how
IMA-appraisal addresses READING_FIRMWARE_PREALLOC_BUFFER.

Mimi

> here
> are bits of code from: security/integrity/ima/ima_main.c:
> 
> static int read_idmap[READING_MAX_ID] = {
>          [READING_FIRMWARE] = FIRMWARE_CHECK,
>          [READING_MODULE] = MODULE_CHECK,
>          [READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
>          [READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
>          [READING_POLICY] = POLICY_CHECK
> };
> 
> int ima_post_read_file(struct file *file, void *buf, loff_t size,
> 	...
>          if (!file && read_id == READING_FIRMWARE) {
>                  if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
>                      (ima_appraise & IMA_APPRAISE_ENFORCE))
>                          return -EACCES; /* INTEGRITY_UNKNOWN */
>                  return 0;
>          }
> 
> Which show that the IMA code is not handling
> READING_FIRMWARE_PREALLOC_BUFFER as it should (I believe it
> should handle it the same as READING_FIRMWARE).
> 
> Now we could fix that, but the only user of
> READING_FIRMWARE_PREALLOC_BUFFER is the code which originally
> introduced it:
> 
> https://patchwork.kernel.org/patch/9162011/
> 
> So I believe it might be better to instead replace it
> with just READING_FIRMWARE and find another way to tell
> kernel_read_file() that there is a pre-allocated buffer,
> perhaps the easiest way there is that  *buf must be
> NULL when the caller wants kernel_read_file() to
> vmalloc the mem. This would of course require auditing
> all callers that the buf which the pass in is initialized
> to NULL.
> 
> Either way adding a third READING_FIRMWARE_FOO to the
> kernel_read_file_id enum seems like a bad idea, from
> the IMA pov firmware is firmware.
> 
> What this whole exercise has shown me though is that
> I need to call security_kernel_post_read_file() when
> loading EFI embedded firmware. I will add a call to
> security_kernel_post_read_file() for v4 of the patch-set.
> 
> > Please Cc Kees in future patches.
> 
> Will do.
> 
> Regards,
> 
> Hans
>