| Message ID | 20221116161642.1670235-6-Jason@zx2c4.com |
|---|---|
| State | New |
| Headers | show |
| Series | Use EFI variables for random seed | expand |
On Wed, 2022-11-16 at 21:08 +0100, Jason A. Donenfeld wrote: > On Wed, Nov 16, 2022 at 8:42 PM James Bottomley > <James.Bottomley@hansenpartnership.com> wrote: > > It would be nice if they could be boot services only ... then they > > disappear naturally, but that would mean the rng would have to > > initialize and save in the EFI stub before ExitBootServices, which > > doesn't seem practical. > > That would be nice, but the whole idea is it gets updated by Linux's > RNG, so that won't work. `boot|runtime` it is, then. But then you can't use the only security mechanism we have in EFI (keeping sensitive information in BS only variables which can only be accessed by EFI signed entities). If you can't take advantage of that then there's no security point in placing the seed in EFI and you might as well simply write it to a file. Artificially trying to hide the variables from efivarfs has no real security value either, as I think you can appreciate if you try the thought experiment of trying to get a VFS modification to hide the random seed file past Al ... I'll get the thought experiment popcorn. James
diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c index d57ee15874f9..08996ba3a373 100644 --- a/fs/efivarfs/file.c +++ b/fs/efivarfs/file.c @@ -76,6 +76,9 @@ static ssize_t efivarfs_file_read(struct file *file, char __user *userbuf, while (!__ratelimit(&file->f_cred->user->ratelimit)) msleep(50); + if (guid_equal(&var->var.VendorGuid, &LINUX_EFI_RANDOM_SEED_TABLE_GUID)) + return -EPERM; + err = efivar_entry_size(var, &datasize); /*
Variables in the random seed GUID must remain secret, so deny all reads to them. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- fs/efivarfs/file.c | 3 +++ 1 file changed, 3 insertions(+)