On Fri, 13 Oct 2023 at 20:56, Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> wrote: > > Hi Sumit > > On Fri, 13 Oct 2023 at 09:53, Sumit Garg <sumit.garg@xxxxxxxxxx> wrote: > > > > Hi Ilias, > > > > On Wed, 11 Oct 2023 at 22:30, Ilias Apalodimas > > <ilias.apalodimas@xxxxxxxxxx> wrote: > > > > > > Kojima-san > > > Apologies for the late reply, I just found some to test this. > > > > > > On Sun, 6 Aug 2023 at 19:55, Masahisa Kojima <masahisa.kojima@xxxxxxxxxx> wrote: > > > > > > > > efivar operation is updated when the tee_stmm_efi module is probed. > > > > tee_stmm_efi module supports SetVariable runtime service, > > > > but user needs to manually remount the efivarfs as RW to enable > > > > the write access if the previous efivar operation does not support > > > > SerVariable and efivarfs is mounted as read-only. > > > > > > > > This commit notifies the update of efivar operation to > > > > efivarfs subsystem, then drops SB_RDONLY flag if the efivar > > > > operation supports SetVariable. > > > > > > The RO->RW transition works fine and I did manage to test basic stuff > > > like setting up efibootmgr options. IIUC the RW->RO should be covered > > > by this patchset [0] ? > > > > Yeah. > > > > > Wouldn't it be better to detect that the tee device of the supplicant > > > closes and use that to switch the permissions? I get why we need that > > > for the TPM, the entire subsystem needs to send TPM commands *before* > > > the supplicant dies. But this is not needed for the EFI variables > > > case, we could just remount the FS as RO the moment the supplicant > > > dies. > > > > As we discussed offline, we should have a unified approach to notify > > kernel TEE client drivers. So the approach implemented as part of [0] > > should address the needs for fTPM as well as EFI. > > Ideally yes, we should have a unified approach. But this is a bit > different IMHO. In the majority of the cases, the supplicant goes > away, we lose access to storage and that's the only thing we care > about. What do you think about in-flight secure storage operations while the tee-supplicant goes away? They can fail abruptly if the tee-supplicant goes away without waiting for them to complete. IMO, the graceful handling should be that the tee-supplicant should be alive when the dependent devices are being closed. For an EFI variable store case as well isn't that a possible scenario? > Only the TPM subsystem is 'special' because it has to perform > a shutdown of the device as well. On top of that, I think we should > try to avoid the kernel depending on userspace apps as much as > possible. There is only tee-supplicant user-space dependency which has to be handled carefully. I am very much up for RPMB fastpath via kernel and get rid of this dependency as well. > I think it's best if we support both of these and add > documentation on why this is happening. Would it be hard to have a > combination of both of your patches? > It won't be hard but there can be corner cases as mentioned above. -Sumit > Thanks > /Ilias > > > > > -Sumit > > > > > > > > [0] https://lore.kernel.org/all/20230728134832.326467-1-sumit.garg@xxxxxxxxxx/ > > > > > > Regards > > > /Ilias > > > > > > > > Signed-off-by: Masahisa Kojima <masahisa.kojima@xxxxxxxxxx> > > > > --- > > > > drivers/firmware/efi/efi.c | 6 ++++++ > > > > drivers/firmware/efi/vars.c | 8 ++++++++ > > > > fs/efivarfs/super.c | 33 +++++++++++++++++++++++++++++++++ > > > > include/linux/efi.h | 8 ++++++++ > > > > 4 files changed, 55 insertions(+) > > > > > > > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c > > > > index 53ae25bbb6ac..d2eec5ed8e5e 100644 > > > > --- a/drivers/firmware/efi/efi.c > > > > +++ b/drivers/firmware/efi/efi.c > > > > @@ -32,6 +32,7 @@ > > > > #include <linux/ucs2_string.h> > > > > #include <linux/memblock.h> > > > > #include <linux/security.h> > > > > +#include <linux/notifier.h> > > > > > > > > #include <asm/early_ioremap.h> > > > > > > > > @@ -187,6 +188,9 @@ static const struct attribute_group efi_subsys_attr_group = { > > > > .is_visible = efi_attr_is_visible, > > > > }; > > > > > > > > +struct blocking_notifier_head efivar_ops_nh; > > > > +EXPORT_SYMBOL_GPL(efivar_ops_nh); > > > > + > > > > static struct efivars generic_efivars; > > > > static struct efivar_operations generic_ops; > > > > > > > > @@ -427,6 +431,8 @@ static int __init efisubsys_init(void) > > > > platform_device_register_simple("efivars", 0, NULL, 0); > > > > } > > > > > > > > + BLOCKING_INIT_NOTIFIER_HEAD(&efivar_ops_nh); > > > > + > > > > error = sysfs_create_group(efi_kobj, &efi_subsys_attr_group); > > > > if (error) { > > > > pr_err("efi: Sysfs attribute export failed with error %d.\n", > > > > diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c > > > > index e9dc7116daf1..f654e6f6af87 100644 > > > > --- a/drivers/firmware/efi/vars.c > > > > +++ b/drivers/firmware/efi/vars.c > > > > @@ -63,6 +63,7 @@ int efivars_register(struct efivars *efivars, > > > > const struct efivar_operations *ops) > > > > { > > > > int rv; > > > > + int event; > > > > > > > > if (down_interruptible(&efivars_lock)) > > > > return -EINTR; > > > > @@ -77,6 +78,13 @@ int efivars_register(struct efivars *efivars, > > > > > > > > __efivars = efivars; > > > > > > > > + if (efivar_supports_writes()) > > > > + event = EFIVAR_OPS_RDWR; > > > > + else > > > > + event = EFIVAR_OPS_RDONLY; > > > > + > > > > + blocking_notifier_call_chain(&efivar_ops_nh, event, NULL); > > > > + > > > > pr_info("Registered efivars operations\n"); > > > > rv = 0; > > > > out: > > > > diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c > > > > index e028fafa04f3..0f6e4d223aea 100644 > > > > --- a/fs/efivarfs/super.c > > > > +++ b/fs/efivarfs/super.c > > > > @@ -14,11 +14,36 @@ > > > > #include <linux/slab.h> > > > > #include <linux/magic.h> > > > > #include <linux/statfs.h> > > > > +#include <linux/notifier.h> > > > > > > > > #include "internal.h" > > > > > > > > LIST_HEAD(efivarfs_list); > > > > > > > > +struct efivarfs_info { > > > > + struct super_block *sb; > > > > + struct notifier_block nb; > > > > +}; > > > > + > > > > +static struct efivarfs_info info; > > > > + > > > > +static int efivarfs_ops_notifier(struct notifier_block *nb, unsigned long event, > > > > + void *data) > > > > +{ > > > > + switch (event) { > > > > + case EFIVAR_OPS_RDONLY: > > > > + info.sb->s_flags |= SB_RDONLY; > > > > + break; > > > > + case EFIVAR_OPS_RDWR: > > > > + info.sb->s_flags &= ~SB_RDONLY; > > > > + break; > > > > + default: > > > > + return NOTIFY_DONE; > > > > + } > > > > + > > > > + return NOTIFY_OK; > > > > +} > > > > + > > > > static void efivarfs_evict_inode(struct inode *inode) > > > > { > > > > clear_inode(inode); > > > > @@ -255,6 +280,12 @@ static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc) > > > > if (!root) > > > > return -ENOMEM; > > > > > > > > + info.sb = sb; > > > > + info.nb.notifier_call = efivarfs_ops_notifier; > > > > + err = blocking_notifier_chain_register(&efivar_ops_nh, &info.nb); > > > > + if (err) > > > > + return err; > > > > + > > > > INIT_LIST_HEAD(&efivarfs_list); > > > > > > > > err = efivar_init(efivarfs_callback, (void *)sb, true, &efivarfs_list); > > > > @@ -281,6 +312,8 @@ static int efivarfs_init_fs_context(struct fs_context *fc) > > > > > > > > static void efivarfs_kill_sb(struct super_block *sb) > > > > { > > > > + blocking_notifier_chain_unregister(&efivar_ops_nh, &info.nb); > > > > + info.sb = NULL; > > > > kill_litter_super(sb); > > > > > > > > if (!efivar_is_available()) > > > > diff --git a/include/linux/efi.h b/include/linux/efi.h > > > > index 603bba2d6437..17cd628b5c42 100644 > > > > --- a/include/linux/efi.h > > > > +++ b/include/linux/efi.h > > > > @@ -1365,6 +1365,14 @@ bool efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table) > > > > > > > > umode_t efi_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n); > > > > > > > > +/* > > > > + * efivar ops event type > > > > + */ > > > > +#define EFIVAR_OPS_RDONLY 0 > > > > +#define EFIVAR_OPS_RDWR 1 > > > > + > > > > +extern struct blocking_notifier_head efivar_ops_nh; > > > > + > > > > void efivars_generic_ops_register(void); > > > > void efivars_generic_ops_unregister(void); > > > > > > > > -- > > > > 2.30.2 > > > >
